Adding upstream version 7.0.14-dfsg.upstream/7.0.14-dfsg

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

34 files changed, 16767 insertions, 0 deletions

diff --git a/src/VBox/NetworkServices/NAT/Makefile.kmk b/src/VBox/NetworkServices/NAT/Makefile.kmk
new file mode 100644
index 00000000..6e9a1917
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/Makefile.kmk
@@ -0,0 +1,162 @@
+# $Id: Makefile.kmk $
+## @file
+# Sub-makefile for NAT Networking
+#
+
+#
+# Copyright (C) 2006-2023 Oracle and/or its affiliates.
+#
+# This file is part of VirtualBox base platform packages, as
+# available from https://www.virtualbox.org.
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation, in version 3 of the
+# License.
+#
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, see <https://www.gnu.org/licenses>.
+#
+# SPDX-License-Identifier: GPL-3.0-only
+#
+
+SUB_DEPTH = ../../../..
+include $(KBUILD_PATH)/subheader.kmk
+ifdef VBOX_WITH_LWIP_NAT # entire file
+
+ ifndef LWIP_SOURCES
+  include $(PATH_SUB_CURRENT)/../../Devices/Network/lwip-new/Config.kmk
+ endif
+
+ #
+ # Globals
+ #
+ VBOX_PATH_NAT_SRC := $(PATH_SUB_CURRENT)
+
+
+ #
+ # Hardened stub exe for VBoxNetNAT.
+ #
+ ifdef VBOX_WITH_HARDENING
+  PROGRAMS += VBoxNetNATHardened
+  VBoxNetNATHardened_TEMPLATE = VBoxR3HardenedExe
+  VBoxNetNATHardened_NAME   = VBoxNetNAT
+  ifdef VBOX_WITH_AUTOMATIC_DEFS_QUOTING
+   VBoxNetNATHardened_DEFS  = SERVICE_NAME="VBoxNetNAT"
+  else
+   VBoxNetNATHardened_DEFS  = SERVICE_NAME=\"VBoxNetNAT\"
+  endif
+  VBoxNetNATHardened_SOURCES = VBoxNetNATHardened.cpp
+  VBoxNetNATHardened_LDFLAGS.win = /SUBSYSTEM:windows
+  $(call VBOX_SET_VER_INFO_EXE,VBoxNetNATHardened,VirtualBox NAT Engine,$(VBOX_WINDOWS_ICON_FILE)) # Version info / description.
+ endif
+
+
+ #
+ # VBoxNetNAT.
+ #
+ ifdef VBOX_WITH_HARDENING
+  DLLS   += VBoxNetNAT
+ else
+  PROGRAMS += VBoxNetNAT
+ endif
+ VBoxNetNAT_TEMPLATE := $(if-expr defined(VBOX_WITH_HARDENING),VBoxMainDll,VBoxMainClientExe)
+ VBoxNetNAT_NAME    := VBoxNetNAT
+ VBoxNetNAT_DEFS     = \
+ 	IPv6 \
+ 	$(if $(VBOX_WITH_INTNET_SERVICE_IN_R3),VBOX_WITH_INTNET_SERVICE_IN_R3,)
+ # VBoxNetNAT_DEFS.linux = WITH_VALGRIND # instrument lwip memp.c
+ VBoxNetNAT_DEFS.win = VBOX_COM_OUTOFPROC_MODULE _WIN32_WINNT=0x501 # Windows XP
+ # Convince Solaris headers to expose socket stuff we need.
+ #
+ # Setting _XOPEN_SOURCE to either 500 or 600 would always work, but
+ # <sys/feature_tests.h> insists that 600 requires C99 and so it
+ # explodes for older g++.  It also insists that 500 is NOT to be used
+ # with C99.
+ #
+ # Newer g++ in C++11 mode (formerly known as C++0x) needs 600, so it
+ # employs sleight of hand to pretend it's C99 to keep feature test
+ # happy.
+ #
+ # Compile the C code with settings that match g++.  This probably
+ # should be centralized so that whole codebase uses consistent
+ # settings.
+ ifeq ($(KBUILD_TARGET),solaris)
+  ifneq ($(VBOX_GCC_VERSION_CXX),)
+   if $(VBOX_GCC_VERSION_CXX) >= 40600
+    # we compile C++ code with -std=c++0x / -std=c++11
+    VBoxNetNAT_CFLAGS.solaris += -std=c99
+    VBoxNetNAT_DEFS.solaris += _XOPEN_SOURCE=600
+   else
+    VBoxNetNAT_DEFS.solaris += _XOPEN_SOURCE=500
+   endif
+  endif
+  VBoxNetNAT_DEFS.solaris += __EXTENSIONS__=1
+ endif
+
+ # (current dir is for for lwipopts.h)
+ VBoxNetNAT_INCS += . $(addprefix ../../Devices/Network/lwip-new/,$(LWIP_INCS))
+
+ VBoxNetNAT_SOURCES = \
+ 	VBoxNetLwipNAT.cpp \
+ 	../NetLib/IntNetIf.cpp \
+ 	../NetLib/VBoxNetPortForwardString.cpp \
+ 	$(addprefix ../../Devices/Network/lwip-new/,$(LWIP_SOURCES)) \
+ 	proxy_pollmgr.c \
+ 	proxy_rtadvd.c \
+ 	proxy.c \
+ 	pxremap.c \
+ 	pxtcp.c \
+ 	pxudp.c \
+ 	pxdns.c \
+ 	fwtcp.c \
+ 	fwudp.c \
+ 	portfwd.c \
+ 	proxy_dhcp6ds.c \
+ 	proxy_tftpd.c
+
+ ifeq ($(KBUILD_TARGET),win)
+  VBoxNetNAT_SOURCES += pxping_win.c # unprivileged Icmp API
+ else
+  VBoxNetNAT_SOURCES      += pxping.c     # raw sockets
+  VBoxNetNAT_CFLAGS.linux += -Wno-address-of-packed-member # Needed for GCC 9.
+ endif
+
+ VBoxNetNAT_SOURCES.darwin += rtmon_bsd.c
+ VBoxNetNAT_SOURCES.freebsd += rtmon_bsd.c
+ VBoxNetNAT_SOURCES.linux  += rtmon_linux.c
+ VBoxNetNAT_SOURCES.solaris += rtmon_bsd.c
+ VBoxNetNAT_SOURCES.win    += \
+ 	rtmon_win.c \
+ 	RTWinPoll.cpp \
+ 	RTWinSocketPair.cpp
+
+ VBoxNetNAT_LIBS = \
+ 	$(LIB_RUNTIME)
+ VBoxNetNAT_LIBS.solaris += socket nsl
+
+ VBoxNetNAT_LDFLAGS.win = /SUBSYSTEM:windows
+
+ # ifeq ($(VBOX_WITH_HARDENING),)
+ #  ifn1of ($(KBUILD_TARGET), darwin win)
+ #   # helper for debugging unprivileged
+ #   VBoxNetNAT_DEFS += VBOX_RAWSOCK_DEBUG_HELPER
+ #   VBoxNetNAT_SOURCES += getrawsock.c
+ #  endif
+ # endif
+
+
+ ifdef VBOX_WITH_HARDENING
+  $(call VBOX_SET_VER_INFO_DLL,VBoxNetNAT,VirtualBox NAT Engine (dll),$(VBOX_WINDOWS_ICON_FILE)) # Version info / description.
+ else
+  $(call VBOX_SET_VER_INFO_EXE,VBoxNetNAT,VirtualBox NAT Engine,$(VBOX_WINDOWS_ICON_FILE)) # Version info / description.
+ endif
+
+endif # VBOX_WITH_LWIP_NAT
+include $(FILE_KBUILD_SUB_FOOTER)
+
diff --git a/src/VBox/NetworkServices/NAT/RTWinPoll.cpp b/src/VBox/NetworkServices/NAT/RTWinPoll.cpp
new file mode 100644
index 00000000..c1cf2707
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/RTWinPoll.cpp
@@ -0,0 +1,164 @@
+/* $Id: RTWinPoll.cpp $ */
+/** @file
+ * NAT Network - poll(2) implementation for winsock.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+#define LOG_GROUP LOG_GROUP_NAT_SERVICE
+
+#include <iprt/asm.h>
+#include <iprt/assert.h>
+#include <iprt/cdefs.h>
+#include <iprt/errcore.h>
+#include <iprt/string.h>
+
+#include <iprt/errcore.h>
+#include <VBox/log.h>
+
+#include <iprt/win/winsock2.h>
+#include <iprt/win/windows.h>
+#include "winpoll.h"
+
+static HANDLE g_hNetworkEvent;
+
+int
+RTWinPoll(struct pollfd *pFds, unsigned int nfds, int timeout, int *pNready)
+{
+    AssertPtrReturn(pFds, VERR_INVALID_PARAMETER);
+
+    if (g_hNetworkEvent == WSA_INVALID_EVENT)
+    {
+        g_hNetworkEvent = WSACreateEvent();
+        AssertReturn(g_hNetworkEvent != WSA_INVALID_EVENT, VERR_INTERNAL_ERROR);
+    }
+
+    for (unsigned int i = 0; i < nfds; ++i)
+    {
+        long eventMask = 0;
+        short pollEvents = pFds[i].events;
+
+        /* clean revents */
+        pFds[i].revents = 0;
+
+        /* ignore invalid sockets */
+        if (pFds[i].fd == INVALID_SOCKET)
+          continue;
+
+        /*
+         * POLLIN         Data other than high priority data may be read without blocking.
+         * This is equivalent to ( POLLRDNORM | POLLRDBAND ).
+         * POLLRDBAND     Priority data may be read without blocking.
+         * POLLRDNORM     Normal data may be read without blocking.
+         */
+        if (pollEvents & POLLIN)
+            eventMask |= FD_READ | FD_ACCEPT;
+
+        /*
+         * POLLOUT        Normal data may be written without blocking.  This is equivalent
+         *  to POLLWRNORM.
+         * POLLWRNORM     Normal data may be written without blocking.
+         */
+        if (pollEvents & POLLOUT)
+            eventMask |= FD_WRITE | FD_CONNECT;
+
+        /*
+         * This is "moral" equivalent to POLLHUP.
+         */
+        eventMask |= FD_CLOSE;
+        WSAEventSelect(pFds[i].fd, g_hNetworkEvent, eventMask);
+    }
+
+    DWORD index = WSAWaitForMultipleEvents(1,
+                                           &g_hNetworkEvent,
+                                           FALSE,
+                                           timeout == RT_INDEFINITE_WAIT ? WSA_INFINITE : timeout,
+                                           FALSE);
+    if (index != WSA_WAIT_EVENT_0)
+    {
+        if (index == WSA_WAIT_TIMEOUT)
+            return VERR_TIMEOUT;
+    }
+
+    int nready = 0;
+    for (unsigned int i = 0; i < nfds; ++i)
+    {
+        short revents = 0;
+        WSANETWORKEVENTS NetworkEvents;
+        int err;
+
+        if (pFds[i].fd == INVALID_SOCKET)
+            continue;
+
+        RT_ZERO(NetworkEvents);
+
+        err = WSAEnumNetworkEvents(pFds[i].fd,
+                                   g_hNetworkEvent,
+                                   &NetworkEvents);
+
+        if (err == SOCKET_ERROR)
+        {
+            if (WSAGetLastError() == WSAENOTSOCK)
+            {
+                pFds[i].revents = POLLNVAL;
+                ++nready;
+            }
+            continue;
+        }
+
+        /* deassociate socket with event */
+        WSAEventSelect(pFds[i].fd, g_hNetworkEvent, 0);
+
+#define WSA_TO_POLL(_wsaev, _pollev)                                    \
+        do {                                                            \
+            if (NetworkEvents.lNetworkEvents & (_wsaev)) {              \
+                revents |= (_pollev);                                   \
+                if (NetworkEvents.iErrorCode[_wsaev##_BIT] != 0) {      \
+                    Log2(("sock %d: %s: %R[sockerr]\n",                 \
+                          pFds[i].fd, #_wsaev,                          \
+                          NetworkEvents.iErrorCode[_wsaev##_BIT]));     \
+                    revents |= POLLERR;                                 \
+                }                                                       \
+            }                                                           \
+        } while (0)
+
+        WSA_TO_POLL(FD_READ,    POLLIN);
+        WSA_TO_POLL(FD_ACCEPT,  POLLIN);
+        WSA_TO_POLL(FD_WRITE,   POLLOUT);
+        WSA_TO_POLL(FD_CONNECT, POLLOUT);
+        WSA_TO_POLL(FD_CLOSE,   POLLHUP | (pFds[i].events & POLLIN));
+
+        Assert((revents & ~(pFds[i].events | POLLHUP | POLLERR)) == 0);
+
+        if (revents != 0)
+        {
+            pFds[i].revents = revents;
+            ++nready;
+        }
+    }
+    WSAResetEvent(g_hNetworkEvent);
+
+    if (pNready)
+      *pNready = nready;
+
+    return VINF_SUCCESS;
+}
diff --git a/src/VBox/NetworkServices/NAT/RTWinSocketPair.cpp b/src/VBox/NetworkServices/NAT/RTWinSocketPair.cpp
new file mode 100644
index 00000000..5b405bee
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/RTWinSocketPair.cpp
@@ -0,0 +1,235 @@
+/* $Id: RTWinSocketPair.cpp $ */
+/** @file
+ * NAT Network - socketpair(2) emulation for winsock.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#include <iprt/asm.h>
+#include <iprt/assert.h>
+#include <iprt/cdefs.h>
+#include <iprt/errcore.h>
+
+#include <iprt/errcore.h>
+
+#include <iprt/win/winsock2.h>
+#include <iprt/win/windows.h>
+
+#include <stdio.h>
+#include <iprt/log.h>
+
+extern "C" int RTWinSocketPair(int domain, int type, int protocol, SOCKET socket_vector[2])
+{
+    LogFlowFunc(("ENTER: domain:%d, type:%d, protocol:%d, socket_vector:%p\n",
+                 domain, type, protocol, socket_vector));
+    switch (domain)
+    {
+    case AF_INET:
+        break;
+    case AF_INET6: /* I dobt we really need it. */
+    default:
+        AssertMsgFailedReturn(("Unsuported domain:%d\n", domain),
+                              VERR_INVALID_PARAMETER);
+    }
+
+    switch(type)
+    {
+    case SOCK_STREAM:
+    case SOCK_DGRAM:
+        break;
+    default:
+        AssertMsgFailedReturn(("Unsuported type:%d\n", type),
+                              VERR_INVALID_PARAMETER);
+    }
+
+    AssertPtrReturn(socket_vector, VERR_INVALID_PARAMETER);
+    if (!socket_vector)
+      return VERR_INVALID_PARAMETER;
+
+    socket_vector[0] = socket_vector[1] = INVALID_SOCKET;
+
+    SOCKET listener = INVALID_SOCKET;
+
+    union {
+        struct sockaddr_in in_addr;
+        struct sockaddr addr;
+    } sa[2];
+
+    int cb = sizeof(sa);
+    memset(&sa, 0, cb);
+
+    sa[0].in_addr.sin_family = domain;
+    sa[0].in_addr.sin_addr.s_addr = RT_H2N_U32(INADDR_LOOPBACK);
+    sa[0].in_addr.sin_port = 0;
+    cb = sizeof(sa[0]);
+
+    if (type == SOCK_STREAM)
+    {
+        listener = WSASocket(domain, type, protocol, 0, NULL, 0);
+
+        if (listener == INVALID_SOCKET)
+        {
+            return VERR_INTERNAL_ERROR;
+        }
+
+        int reuse = 1;
+        cb = sizeof(int);
+        int rc = setsockopt(listener, SOL_SOCKET, SO_REUSEADDR, (char *)&reuse, cb);
+
+        if (rc)
+        {
+            goto close_socket;
+        }
+
+        cb = sizeof(sa[0]);
+        rc = bind(listener, &sa[0].addr, cb);
+        if(rc)
+        {
+            goto close_socket;
+        }
+
+        memset(&sa[0], 0, cb);
+        rc = getsockname(listener, &sa[0].addr, &cb);
+        if (rc)
+        {
+            goto close_socket;
+        }
+
+        rc = listen(listener, 1);
+        if (rc)
+        {
+            goto close_socket;
+        }
+
+        socket_vector[0] = WSASocket(domain, type, protocol, 0, NULL, 0);
+        if (socket_vector[0] == INVALID_SOCKET)
+        {
+            goto close_socket;
+        }
+
+        rc = connect(socket_vector[0], &sa[0].addr, cb);
+        if (rc)
+          goto close_socket;
+
+
+        socket_vector[1] = accept(listener, NULL, NULL);
+        if (socket_vector[1] == INVALID_SOCKET)
+        {
+            goto close_socket;
+        }
+
+        closesocket(listener);
+    }
+    else
+    {
+        socket_vector[0] = WSASocket(domain, type, protocol, 0, NULL, 0);
+
+        cb = sizeof(sa[0]);
+        int rc = bind(socket_vector[0], &sa[0].addr, cb);
+        Assert(rc != SOCKET_ERROR);
+        if (rc == SOCKET_ERROR)
+        {
+            goto close_socket;
+        }
+
+        sa[1].in_addr.sin_family = domain;
+        sa[1].in_addr.sin_addr.s_addr = RT_H2N_U32(INADDR_LOOPBACK);
+        sa[1].in_addr.sin_port = 0;
+
+        socket_vector[1] = WSASocket(domain, type, protocol, 0, NULL, 0);
+        rc = bind(socket_vector[1], &sa[1].addr, cb);
+        Assert(rc != SOCKET_ERROR);
+        if (rc == SOCKET_ERROR)
+        {
+            goto close_socket;
+        }
+
+        {
+            u_long mode = 0;
+            rc = ioctlsocket(socket_vector[0], FIONBIO, &mode);
+            AssertMsgReturn(rc != SOCKET_ERROR,
+                            ("ioctl error: %d\n", WSAGetLastError()),
+                            VERR_INTERNAL_ERROR);
+
+            rc = ioctlsocket(socket_vector[1], FIONBIO, &mode);
+            AssertMsgReturn(rc != SOCKET_ERROR,
+                            ("ioctl error: %d\n", WSAGetLastError()),
+                            VERR_INTERNAL_ERROR);
+        }
+
+        memset(&sa, 0, 2 * cb);
+        rc = getsockname(socket_vector[0], &sa[0].addr, &cb);
+        Assert(rc != SOCKET_ERROR);
+        if (rc == SOCKET_ERROR)
+        {
+            goto close_socket;
+        }
+
+        rc = getsockname(socket_vector[1], &sa[1].addr, &cb);
+        Assert(rc != SOCKET_ERROR);
+        if (rc == SOCKET_ERROR)
+        {
+            goto close_socket;
+        }
+
+        rc = connect(socket_vector[0], &sa[1].addr, cb);
+        Assert(rc != SOCKET_ERROR);
+        if (rc == SOCKET_ERROR)
+        {
+            goto close_socket;
+        }
+
+        rc = connect(socket_vector[1], &sa[0].addr, cb);
+        Assert(rc != SOCKET_ERROR);
+        if (rc == SOCKET_ERROR)
+        {
+            goto close_socket;
+        }
+    }
+
+    for (int i = 0; i < 2; ++i) {
+        SOCKET s = socket_vector[i];
+        u_long mode = 1;
+
+        int status = ioctlsocket(s, FIONBIO, &mode);
+        if (status == SOCKET_ERROR) {
+            LogRel(("FIONBIO: %R[sockerr]\n", WSAGetLastError()));
+        }
+    }
+
+    LogFlowFuncLeaveRC(VINF_SUCCESS);
+    return VINF_SUCCESS;
+
+close_socket:
+    if (listener != INVALID_SOCKET)
+      closesocket(listener);
+
+    if (socket_vector[0] != INVALID_SOCKET)
+      closesocket(socket_vector[0]);
+
+    if (socket_vector[1] != INVALID_SOCKET)
+      closesocket(socket_vector[1]);
+
+    LogFlowFuncLeaveRC(VERR_INTERNAL_ERROR);
+    return VERR_INTERNAL_ERROR;
+}
diff --git a/src/VBox/NetworkServices/NAT/VBoxNetLwipNAT.cpp b/src/VBox/NetworkServices/NAT/VBoxNetLwipNAT.cpp
new file mode 100644
index 00000000..b07d404c
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/VBoxNetLwipNAT.cpp
@@ -0,0 +1,2352 @@
+/* $Id: VBoxNetLwipNAT.cpp $ */
+/** @file
+ * VBoxNetNAT - NAT Service for connecting to IntNet.
+ */
+
+/*
+ * Copyright (C) 2009-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+/* Must be included before winutils.h (lwip/def.h), otherwise Windows build breaks. */
+#define LOG_GROUP LOG_GROUP_NAT_SERVICE
+
+#include "winutils.h"
+
+#include <VBox/com/assert.h>
+#include <VBox/com/com.h>
+#include <VBox/com/listeners.h>
+#include <VBox/com/string.h>
+#include <VBox/com/Guid.h>
+#include <VBox/com/array.h>
+#include <VBox/com/ErrorInfo.h>
+#include <VBox/com/errorprint.h>
+#include <VBox/com/VirtualBox.h>
+#include <VBox/com/NativeEventQueue.h>
+
+#include <iprt/net.h>
+#include <iprt/initterm.h>
+#include <iprt/alloca.h>
+#ifndef RT_OS_WINDOWS
+# include <arpa/inet.h>
+#endif
+#include <iprt/err.h>
+#include <iprt/time.h>
+#include <iprt/timer.h>
+#include <iprt/thread.h>
+#include <iprt/stream.h>
+#include <iprt/path.h>
+#include <iprt/param.h>
+#include <iprt/pipe.h>
+#include <iprt/string.h>
+#include <iprt/mem.h>
+#include <iprt/message.h>
+#include <iprt/req.h>
+#include <iprt/file.h>
+#include <iprt/semaphore.h>
+#include <iprt/cpp/utils.h>
+#include <VBox/log.h>
+
+#include <iprt/buildconfig.h>
+#include <iprt/getopt.h>
+#include <iprt/process.h>
+
+#include <VBox/sup.h>
+#include <VBox/intnet.h>
+#include <VBox/intnetinline.h>
+#include <VBox/vmm/pdmnetinline.h>
+#include <VBox/vmm/vmm.h>
+#include <VBox/version.h>
+
+#ifndef RT_OS_WINDOWS
+# include <sys/poll.h>
+# include <sys/socket.h>
+# include <netinet/in.h>
+# ifdef RT_OS_LINUX
+#  include <linux/icmp.h>       /* ICMP_FILTER */
+# endif
+# include <netinet/icmp6.h>
+#endif
+
+#include <map>
+#include <vector>
+#include <iprt/sanitized/string>
+
+#include <stdio.h>
+
+#include "../NetLib/IntNetIf.h"
+#include "../NetLib/VBoxPortForwardString.h"
+
+extern "C"
+{
+/* bunch of LWIP headers */
+#include "lwip/sys.h"
+#include "lwip/pbuf.h"
+#include "lwip/netif.h"
+#include "lwip/ethip6.h"
+#include "lwip/nd6.h"           // for proxy_na_hook
+#include "lwip/mld6.h"
+#include "lwip/tcpip.h"
+#include "netif/etharp.h"
+
+#include "proxy.h"
+#include "pxremap.h"
+#include "portfwd.h"
+}
+
+#include "VBoxLwipCore.h"
+
+#ifdef VBOX_RAWSOCK_DEBUG_HELPER
+#if    defined(VBOX_WITH_HARDENING) /* obviously */     \
+    || defined(RT_OS_WINDOWS)       /* not used */      \
+    || defined(RT_OS_DARWIN)        /* not necessary */
+# error Have you forgotten to turn off VBOX_RAWSOCK_DEBUG_HELPER?
+#endif
+/* ask the privileged helper to create a raw socket for us */
+extern "C" int getrawsock(int type);
+#endif
+
+
+
+typedef struct NATSERVICEPORTFORWARDRULE
+{
+    PORTFORWARDRULE Pfr;
+    fwspec         FWSpec;
+} NATSERVICEPORTFORWARDRULE, *PNATSERVICEPORTFORWARDRULE;
+
+typedef std::vector<NATSERVICEPORTFORWARDRULE> VECNATSERVICEPF;
+typedef VECNATSERVICEPF::iterator ITERATORNATSERVICEPF;
+typedef VECNATSERVICEPF::const_iterator CITERATORNATSERVICEPF;
+
+
+class VBoxNetLwipNAT
+{
+    static RTGETOPTDEF s_aGetOptDef[];
+
+    com::Utf8Str m_strNetworkName;
+    int m_uVerbosity;
+
+    ComPtr<IVirtualBoxClient> virtualboxClient;
+    ComPtr<IVirtualBox> virtualbox;
+    ComPtr<IHost> m_host;
+    ComPtr<INATNetwork> m_net;
+
+    RTMAC m_MacAddress;
+    INTNETIFCTX m_hIf;
+    RTTHREAD m_hThrRecv;
+
+    /** Home folder location; used as default directory for several paths. */
+    com::Utf8Str m_strHome;
+
+    struct proxy_options m_ProxyOptions;
+    struct sockaddr_in m_src4;
+    struct sockaddr_in6 m_src6;
+    /**
+     * place for registered local interfaces.
+     */
+    ip4_lomap m_lo2off[10];
+    ip4_lomap_desc m_loOptDescriptor;
+
+    uint16_t m_u16Mtu;
+    netif m_LwipNetIf;
+
+    VECNATSERVICEPF m_vecPortForwardRule4;
+    VECNATSERVICEPF m_vecPortForwardRule6;
+
+    class Listener
+    {
+        class Adapter;
+        typedef ListenerImpl<Adapter, VBoxNetLwipNAT *> Impl;
+
+        ComObjPtr<Impl> m_pListenerImpl;
+        ComPtr<IEventSource> m_pEventSource;
+
+    public:
+        HRESULT init(VBoxNetLwipNAT *pNAT);
+        void uninit();
+
+        template <typename IEventful>
+        HRESULT listen(const ComPtr<IEventful> &pEventful,
+                       const VBoxEventType_T aEvents[]);
+        HRESULT unlisten();
+
+    private:
+        HRESULT doListen(const ComPtr<IEventSource> &pEventSource,
+                         const VBoxEventType_T aEvents[]);
+    };
+
+    Listener m_ListenerNATNet;
+    Listener m_ListenerVirtualBox;
+    Listener m_ListenerVBoxClient;
+
+public:
+    VBoxNetLwipNAT();
+    ~VBoxNetLwipNAT();
+
+    RTEXITCODE parseArgs(int argc, char *argv[]);
+
+    int init();
+    int run();
+    void shutdown();
+
+private:
+    RTEXITCODE usage();
+
+    int initCom();
+    int initHome();
+    int initLog();
+    int initIPv4();
+    int initIPv4LoopbackMap();
+    int initIPv6();
+    int initComEvents();
+
+    int getExtraData(com::Utf8Str &strValueOut, const char *pcszKey);
+
+    static void reportError(const char *a_pcszFormat, ...) RT_IPRT_FORMAT_ATTR(1, 2);
+
+    static HRESULT reportComError(ComPtr<IUnknown> iface,
+                                  const com::Utf8Str &strContext,
+                                  HRESULT hrc);
+    static void reportErrorInfoList(const com::ErrorInfo &info,
+                                    const com::Utf8Str &strContext);
+    static void reportErrorInfo(const com::ErrorInfo &info);
+
+    void initIPv4RawSock();
+    void initIPv6RawSock();
+
+    static DECLCALLBACK(void) onLwipTcpIpInit(void *arg);
+    static DECLCALLBACK(void) onLwipTcpIpFini(void *arg);
+    static DECLCALLBACK(err_t) netifInit(netif *pNetif) RT_NOTHROW_PROTO;
+
+    HRESULT HandleEvent(VBoxEventType_T aEventType, IEvent *pEvent);
+
+    const char **getHostNameservers();
+
+    int fetchNatPortForwardRules(VECNATSERVICEPF &vec, bool fIsIPv6);
+    static int natServiceProcessRegisteredPf(VECNATSERVICEPF &vecPf);
+    static int natServicePfRegister(NATSERVICEPORTFORWARDRULE &natServicePf);
+
+    static DECLCALLBACK(int) receiveThread(RTTHREAD hThreadSelf, void *pvUser);
+
+    /* input from intnet */
+    static DECLCALLBACK(void) processFrame(void *pvUser, void *pvFrame, uint32_t cbFrame);
+
+    /* output to intnet */
+    static DECLCALLBACK(err_t) netifLinkoutput(netif *pNetif, pbuf *pBuf) RT_NOTHROW_PROTO;
+};
+
+
+
+VBoxNetLwipNAT::VBoxNetLwipNAT()
+  : m_uVerbosity(0),
+    m_hThrRecv(NIL_RTTHREAD)
+{
+    LogFlowFuncEnter();
+
+    RT_ZERO(m_ProxyOptions.ipv4_addr);
+    RT_ZERO(m_ProxyOptions.ipv4_mask);
+    RT_ZERO(m_ProxyOptions.ipv6_addr);
+    m_ProxyOptions.ipv6_enabled = 0;
+    m_ProxyOptions.ipv6_defroute = 0;
+    m_ProxyOptions.icmpsock4 = INVALID_SOCKET;
+    m_ProxyOptions.icmpsock6 = INVALID_SOCKET;
+    m_ProxyOptions.tftp_root = NULL;
+    m_ProxyOptions.src4 = NULL;
+    m_ProxyOptions.src6 = NULL;
+    RT_ZERO(m_src4);
+    RT_ZERO(m_src6);
+    m_src4.sin_family = AF_INET;
+    m_src6.sin6_family = AF_INET6;
+#if HAVE_SA_LEN
+    m_src4.sin_len = sizeof(m_src4);
+    m_src6.sin6_len = sizeof(m_src6);
+#endif
+    m_ProxyOptions.lomap_desc = NULL;
+    m_ProxyOptions.nameservers = NULL;
+
+    m_LwipNetIf.name[0] = 'N';
+    m_LwipNetIf.name[1] = 'T';
+
+    m_MacAddress.au8[0] = 0x52;
+    m_MacAddress.au8[1] = 0x54;
+    m_MacAddress.au8[2] = 0;
+    m_MacAddress.au8[3] = 0x12;
+    m_MacAddress.au8[4] = 0x35;
+    m_MacAddress.au8[5] = 0;
+
+    RT_ZERO(m_lo2off);
+    m_loOptDescriptor.lomap = NULL;
+    m_loOptDescriptor.num_lomap = 0;
+
+    LogFlowFuncLeave();
+}
+
+
+VBoxNetLwipNAT::~VBoxNetLwipNAT()
+{
+    if (m_ProxyOptions.tftp_root)
+    {
+        RTStrFree((char *)m_ProxyOptions.tftp_root);
+        m_ProxyOptions.tftp_root = NULL;
+    }
+    if (m_ProxyOptions.nameservers)
+    {
+        const char **pv = m_ProxyOptions.nameservers;
+        while (*pv)
+        {
+            RTStrFree((char*)*pv);
+            pv++;
+        }
+        RTMemFree(m_ProxyOptions.nameservers);
+        m_ProxyOptions.nameservers = NULL;
+    }
+}
+
+
+/**
+ * Command line options.
+ */
+RTGETOPTDEF VBoxNetLwipNAT::s_aGetOptDef[] =
+{
+    { "--network",              'n',   RTGETOPT_REQ_STRING },
+    { "--verbose",              'v',   RTGETOPT_REQ_NOTHING },
+};
+
+
+/** Icky hack to tell the caller it should exit with RTEXITCODE_SUCCESS */
+#define RTEXITCODE_DONE RTEXITCODE_32BIT_HACK
+
+RTEXITCODE
+VBoxNetLwipNAT::usage()
+{
+    RTPrintf("%s Version %sr%u\n"
+             "Copyright (C) 2009-" VBOX_C_YEAR " " VBOX_VENDOR "\n"
+             "\n"
+             "Usage: %s <options>\n"
+             "\n"
+             "Options:\n",
+             RTProcShortName(), RTBldCfgVersion(), RTBldCfgRevision(),
+             RTProcShortName());
+    for (size_t i = 0; i < RT_ELEMENTS(s_aGetOptDef); ++i)
+        RTPrintf("    -%c, %s\n", s_aGetOptDef[i].iShort, s_aGetOptDef[i].pszLong);
+
+    return RTEXITCODE_DONE;
+}
+
+
+RTEXITCODE
+VBoxNetLwipNAT::parseArgs(int argc, char *argv[])
+{
+    unsigned int uVerbosity = 0;
+    int rc;
+
+    RTGETOPTSTATE State;
+    rc = RTGetOptInit(&State, argc, argv,
+                      s_aGetOptDef, RT_ELEMENTS(s_aGetOptDef),
+                      1, 0);
+
+    int ch;
+    RTGETOPTUNION Val;
+    while ((ch = RTGetOpt(&State, &Val)) != 0)
+    {
+        switch (ch)
+        {
+            case 'n':           /* --network */
+                if (m_strNetworkName.isNotEmpty())
+                    return RTMsgErrorExit(RTEXITCODE_SYNTAX, "multiple --network options");
+                m_strNetworkName = Val.psz;
+                break;
+
+            case 'v':           /* --verbose */
+                ++uVerbosity;
+                break;
+
+
+            /*
+             * Standard options recognized by RTGetOpt()
+             */
+
+            case 'V':           /* --version */
+                RTPrintf("%sr%u\n", RTBldCfgVersion(), RTBldCfgRevision());
+                return RTEXITCODE_DONE;
+
+            case 'h':           /* --help */
+                return usage();
+
+            case VINF_GETOPT_NOT_OPTION:
+                return RTMsgErrorExit(RTEXITCODE_SYNTAX, "unexpected non-option argument");
+
+            default:
+                return RTGetOptPrintError(ch, &Val);
+        }
+    }
+
+    if (m_strNetworkName.isEmpty())
+        return RTMsgErrorExit(RTEXITCODE_SYNTAX, "missing --network option");
+
+    m_uVerbosity = uVerbosity;
+    return RTEXITCODE_SUCCESS;
+}
+
+
+/**
+ * Perform actual initialization.
+ *
+ * This code runs on the main thread.  Establish COM connection with
+ * VBoxSVC so that we can do API calls.  Starts the LWIP thread.
+ */
+int VBoxNetLwipNAT::init()
+{
+    HRESULT hrc;
+    int rc;
+
+    LogFlowFuncEnter();
+
+    /* Get the COM API set up. */
+    rc = initCom();
+    if (RT_FAILURE(rc))
+        return rc;
+
+    /* Get the home folder location.  It's ok if it fails. */
+    initHome();
+
+    /*
+     * We get the network name on the command line.  Get hold of its
+     * API object to get the rest of the configuration from.
+     */
+    hrc = virtualbox->FindNATNetworkByName(com::Bstr(m_strNetworkName).raw(),
+                                           m_net.asOutParam());
+    if (FAILED(hrc))
+    {
+        reportComError(virtualbox, "FindNATNetworkByName", hrc);
+        return VERR_NOT_FOUND;
+    }
+
+    /*
+     * Now that we know the network name and have ensured that it
+     * indeed exists we can create the release log file.
+     */
+    initLog();
+
+    // resolver changes are reported on vbox but are retrieved from
+    // host so stash a pointer for future lookups
+    hrc = virtualbox->COMGETTER(Host)(m_host.asOutParam());
+    AssertComRCReturn(hrc, VERR_INTERNAL_ERROR);
+
+
+    /* Get the settings related to IPv4. */
+    rc = initIPv4();
+    if (RT_FAILURE(rc))
+        return rc;
+
+    /* Get the settings related to IPv6. */
+    rc = initIPv6();
+    if (RT_FAILURE(rc))
+        return rc;
+
+
+    fetchNatPortForwardRules(m_vecPortForwardRule4, /* :fIsIPv6 */ false);
+    if (m_ProxyOptions.ipv6_enabled)
+        fetchNatPortForwardRules(m_vecPortForwardRule6, /* :fIsIPv6 */ true);
+
+
+    if (m_strHome.isNotEmpty())
+    {
+        com::Utf8StrFmt strTftpRoot("%s%c%s", m_strHome.c_str(), RTPATH_DELIMITER, "TFTP");
+        char *pszStrTemp;       // avoid const char ** vs char **
+        rc = RTStrUtf8ToCurrentCP(&pszStrTemp, strTftpRoot.c_str());
+        AssertRC(rc);
+        m_ProxyOptions.tftp_root = pszStrTemp;
+    }
+
+    m_ProxyOptions.nameservers = getHostNameservers();
+
+    initComEvents();
+    /* end of COM initialization */
+
+    /* connect to the intnet */
+    rc = IntNetR3IfCreate(&m_hIf, m_strNetworkName.c_str());
+    if (RT_SUCCESS(rc))
+        rc = IntNetR3IfSetActive(m_hIf, true /*fActive*/);
+
+    LogFlowFuncLeaveRC(rc);
+    return rc;
+}
+
+
+/**
+ * Primary COM initialization performed on the main thread.
+ *
+ * This initializes COM and obtains VirtualBox Client and VirtualBox
+ * objects.
+ *
+ * @note The member variables for them are in the base class.  We
+ * currently do it here so that we can report errors properly, because
+ * the base class' VBoxNetBaseService::init() is a bit naive and
+ * fixing that would just create unnecessary churn for little
+ * immediate gain.  It's easier to ignore the base class code and do
+ * it ourselves and do the refactoring later.
+ */
+int VBoxNetLwipNAT::initCom()
+{
+    HRESULT hrc;
+
+    hrc = com::Initialize();
+    if (FAILED(hrc))
+    {
+#ifdef VBOX_WITH_XPCOM
+        if (hrc == NS_ERROR_FILE_ACCESS_DENIED)
+        {
+            char szHome[RTPATH_MAX] = "";
+            int vrc = com::GetVBoxUserHomeDirectory(szHome, sizeof(szHome), false);
+            if (RT_SUCCESS(vrc))
+            {
+                return RTMsgErrorExit(RTEXITCODE_INIT,
+                                      "Failed to initialize COM: %s: %Rhrf",
+                                      szHome, hrc);
+            }
+        }
+#endif  /* VBOX_WITH_XPCOM */
+        return RTMsgErrorExit(RTEXITCODE_INIT,
+                              "Failed to initialize COM: %Rhrf", hrc);
+    }
+
+    hrc = virtualboxClient.createInprocObject(CLSID_VirtualBoxClient);
+    if (FAILED(hrc))
+    {
+        reportError("Failed to create VirtualBox Client object: %Rhra", hrc);
+        return VERR_GENERAL_FAILURE;
+    }
+
+    hrc = virtualboxClient->COMGETTER(VirtualBox)(virtualbox.asOutParam());
+    if (FAILED(hrc))
+    {
+        reportError("Failed to obtain VirtualBox object: %Rhra", hrc);
+        return VERR_GENERAL_FAILURE;
+    }
+
+    return VINF_SUCCESS;
+}
+
+
+/**
+ * Get the VirtualBox home folder.
+ *
+ * It is used as the base directory for the default release log file
+ * and for the TFTP root location.
+ */
+int VBoxNetLwipNAT::initHome()
+{
+    HRESULT hrc;
+    int rc;
+
+    com::Bstr bstrHome;
+    hrc = virtualbox->COMGETTER(HomeFolder)(bstrHome.asOutParam());
+    if (SUCCEEDED(hrc))
+    {
+        m_strHome = bstrHome;
+        return VINF_SUCCESS;
+    }
+
+    /*
+     * In the unlikely event that we have failed to retrieve
+     * HomeFolder via the API, try the fallback method.  Note that
+     * despite "com" namespace it does not use COM.
+     */
+    char szHome[RTPATH_MAX] = "";
+    rc = com::GetVBoxUserHomeDirectory(szHome, sizeof(szHome), false);
+    if (RT_SUCCESS(rc))
+    {
+        m_strHome = szHome;
+        return VINF_SUCCESS;
+    }
+
+    return rc;
+}
+
+
+/*
+ * Read IPv4 related settings and do necessary initialization.  These
+ * settings will be picked up by the proxy on the lwIP thread.  See
+ * onLwipTcpIpInit().
+ */
+int VBoxNetLwipNAT::initIPv4()
+{
+    HRESULT hrc;
+    int rc;
+
+    AssertReturn(m_net.isNotNull(), VERR_GENERAL_FAILURE);
+
+
+    /*
+     * IPv4 address and mask.
+     */
+    com::Bstr bstrIPv4Prefix;
+    hrc = m_net->COMGETTER(Network)(bstrIPv4Prefix.asOutParam());
+    if (FAILED(hrc))
+    {
+        reportComError(m_net, "Network", hrc);
+        return VERR_GENERAL_FAILURE;
+    }
+
+    RTNETADDRIPV4 Net4, Mask4;
+    int iPrefixLength;
+    rc = RTNetStrToIPv4Cidr(com::Utf8Str(bstrIPv4Prefix).c_str(),
+                            &Net4, &iPrefixLength);
+    if (RT_FAILURE(rc))
+    {
+        reportError("Failed to parse IPv4 prefix %ls\n", bstrIPv4Prefix.raw());
+        return rc;
+    }
+
+    if (iPrefixLength > 30 || 0 >= iPrefixLength)
+    {
+        reportError("Invalid IPv4 prefix length %d\n", iPrefixLength);
+        return VERR_INVALID_PARAMETER;
+    }
+
+    rc = RTNetPrefixToMaskIPv4(iPrefixLength, &Mask4);
+    AssertRCReturn(rc, rc);
+
+    /** @todo r=uwe Check the address is unicast, not a loopback, etc. */
+
+    RTNETADDRIPV4 Addr4;
+    Addr4.u = Net4.u | RT_H2N_U32_C(0x00000001);
+
+    memcpy(&m_ProxyOptions.ipv4_addr, &Addr4, sizeof(ip_addr));
+    memcpy(&m_ProxyOptions.ipv4_mask, &Mask4, sizeof(ip_addr));
+
+
+    /* Raw socket for ICMP. */
+    initIPv4RawSock();
+
+
+    /* IPv4 source address (host), if configured. */
+    com::Utf8Str strSourceIp4;
+    rc = getExtraData(strSourceIp4, "SourceIp4");
+    if (RT_SUCCESS(rc) && strSourceIp4.isNotEmpty())
+    {
+        RTNETADDRIPV4 addr;
+        rc = RTNetStrToIPv4Addr(strSourceIp4.c_str(), &addr);
+        if (RT_SUCCESS(rc))
+        {
+            m_src4.sin_addr.s_addr = addr.u;
+            m_ProxyOptions.src4 = &m_src4;
+
+            LogRel(("Will use %RTnaipv4 as IPv4 source address\n",
+                    m_src4.sin_addr.s_addr));
+        }
+        else
+        {
+            LogRel(("Failed to parse \"%s\" IPv4 source address specification\n",
+                    strSourceIp4.c_str()));
+        }
+    }
+
+    /* Make host's loopback(s) available from inside the natnet */
+    initIPv4LoopbackMap();
+
+    return VINF_SUCCESS;
+}
+
+
+/**
+ * Create raw IPv4 socket for sending and snooping ICMP.
+ */
+void VBoxNetLwipNAT::initIPv4RawSock()
+{
+    SOCKET icmpsock4 = INVALID_SOCKET;
+
+#ifndef RT_OS_DARWIN
+    const int icmpstype = SOCK_RAW;
+#else
+    /* on OS X it's not privileged */
+    const int icmpstype = SOCK_DGRAM;
+#endif
+
+    icmpsock4 = socket(AF_INET, icmpstype, IPPROTO_ICMP);
+    if (icmpsock4 == INVALID_SOCKET)
+    {
+        perror("IPPROTO_ICMP");
+#ifdef VBOX_RAWSOCK_DEBUG_HELPER
+        icmpsock4 = getrawsock(AF_INET);
+#endif
+    }
+
+    if (icmpsock4 != INVALID_SOCKET)
+    {
+#ifdef ICMP_FILTER              //  Linux specific
+        struct icmp_filter flt = {
+            ~(uint32_t)(
+                  (1U << ICMP_ECHOREPLY)
+                | (1U << ICMP_DEST_UNREACH)
+                | (1U << ICMP_TIME_EXCEEDED)
+            )
+        };
+
+        int status = setsockopt(icmpsock4, SOL_RAW, ICMP_FILTER,
+                                &flt, sizeof(flt));
+        if (status < 0)
+        {
+            perror("ICMP_FILTER");
+        }
+#endif
+    }
+
+    m_ProxyOptions.icmpsock4 = icmpsock4;
+}
+
+
+/**
+ * Init mapping from the natnet's IPv4 addresses to host's IPv4
+ * loopbacks.  Plural "loopbacks" because it's now quite common to run
+ * services on loopback addresses other than 127.0.0.1.  E.g. a
+ * caching dns proxy on 127.0.1.1 or 127.0.0.53.
+ */
+int VBoxNetLwipNAT::initIPv4LoopbackMap()
+{
+    HRESULT hrc;
+    int rc;
+
+    com::SafeArray<BSTR> aStrLocalMappings;
+    hrc = m_net->COMGETTER(LocalMappings)(ComSafeArrayAsOutParam(aStrLocalMappings));
+    if (FAILED(hrc))
+    {
+        reportComError(m_net, "LocalMappings", hrc);
+        return VERR_GENERAL_FAILURE;
+    }
+
+    if (aStrLocalMappings.size() == 0)
+        return VINF_SUCCESS;
+
+
+    /* netmask in host order, to verify the offsets */
+    uint32_t uMask = RT_N2H_U32(ip4_addr_get_u32(&m_ProxyOptions.ipv4_mask));
+
+
+    /*
+     * Process mappings of the form "127.x.y.z=off"
+     */
+    unsigned int dst = 0;      /* typeof(ip4_lomap_desc::num_lomap) */
+    for (size_t i = 0; i < aStrLocalMappings.size(); ++i)
+    {
+        com::Utf8Str strMapping(aStrLocalMappings[i]);
+        const char *pcszRule = strMapping.c_str();
+        LogRel(("IPv4 loopback mapping %zu: %s\n", i, pcszRule));
+
+        RTNETADDRIPV4 Loopback4;
+        char *pszNext;
+        rc = RTNetStrToIPv4AddrEx(pcszRule, &Loopback4, &pszNext);
+        if (RT_FAILURE(rc))
+        {
+            LogRel(("Failed to parse IPv4 address: %Rra\n", rc));
+            continue;
+        }
+
+        if (Loopback4.au8[0] != 127)
+        {
+            LogRel(("Not an IPv4 loopback address\n"));
+            continue;
+        }
+
+        if (rc != VWRN_TRAILING_CHARS)
+        {
+            LogRel(("Missing right hand side\n"));
+            continue;
+        }
+
+        pcszRule = RTStrStripL(pszNext);
+        if (*pcszRule != '=')
+        {
+            LogRel(("Invalid rule format\n"));
+            continue;
+        }
+
+        pcszRule = RTStrStripL(pcszRule+1);
+        if (*pszNext == '\0')
+        {
+            LogRel(("Empty right hand side\n"));
+            continue;
+        }
+
+        uint32_t u32Offset;
+        rc = RTStrToUInt32Ex(pcszRule, &pszNext, 10, &u32Offset);
+        if (rc != VINF_SUCCESS && rc != VWRN_TRAILING_SPACES)
+        {
+            LogRel(("Invalid offset\n"));
+            continue;
+        }
+
+        if (u32Offset <= 1 || u32Offset == ~uMask)
+        {
+            LogRel(("Offset maps to a reserved address\n"));
+            continue;
+        }
+
+        if ((u32Offset & uMask) != 0)
+        {
+            LogRel(("Offset exceeds the network size\n"));
+            continue;
+        }
+
+        if (dst >= RT_ELEMENTS(m_lo2off))
+        {
+            LogRel(("Ignoring the mapping, too many mappings already\n"));
+            continue;
+        }
+
+        ip4_addr_set_u32(&m_lo2off[dst].loaddr, Loopback4.u);
+        m_lo2off[dst].off = u32Offset;
+        ++dst;
+    }
+
+    if (dst > 0)
+    {
+        m_loOptDescriptor.lomap = m_lo2off;
+        m_loOptDescriptor.num_lomap = dst;
+        m_ProxyOptions.lomap_desc = &m_loOptDescriptor;
+    }
+
+    return VINF_SUCCESS;
+}
+
+
+/*
+ * Read IPv6 related settings and do necessary initialization.  These
+ * settings will be picked up by the proxy on the lwIP thread.  See
+ * onLwipTcpIpInit().
+ */
+int VBoxNetLwipNAT::initIPv6()
+{
+    HRESULT hrc;
+    int rc;
+
+    AssertReturn(m_net.isNotNull(), VERR_GENERAL_FAILURE);
+
+
+    /* Is IPv6 enabled for this network at all? */
+    BOOL fIPv6Enabled = FALSE;
+    hrc = m_net->COMGETTER(IPv6Enabled)(&fIPv6Enabled);
+    if (FAILED(hrc))
+    {
+        reportComError(m_net, "IPv6Enabled", hrc);
+        return VERR_GENERAL_FAILURE;
+    }
+
+    m_ProxyOptions.ipv6_enabled = !!fIPv6Enabled;
+    if (!fIPv6Enabled)
+        return VINF_SUCCESS;
+
+
+    /*
+     * IPv6 address.
+     */
+    com::Bstr bstrIPv6Prefix;
+    hrc = m_net->COMGETTER(IPv6Prefix)(bstrIPv6Prefix.asOutParam());
+    if (FAILED(hrc))
+    {
+        reportComError(m_net, "IPv6Prefix", hrc);
+        return VERR_GENERAL_FAILURE;
+    }
+
+    RTNETADDRIPV6 Net6;
+    int iPrefixLength;
+    rc = RTNetStrToIPv6Cidr(com::Utf8Str(bstrIPv6Prefix).c_str(),
+                            &Net6, &iPrefixLength);
+    if (RT_FAILURE(rc))
+    {
+        reportError("Failed to parse IPv6 prefix %ls\n", bstrIPv6Prefix.raw());
+        return rc;
+    }
+
+    /* Allow both addr:: and addr::/64 */
+    if (iPrefixLength == 128)   /* no length was specified after the address? */
+        iPrefixLength = 64;     /*   take it to mean /64 which we require anyway */
+    else if (iPrefixLength != 64)
+    {
+        reportError("Invalid IPv6 prefix length %d,"
+                    " must be 64.\n", iPrefixLength);
+        return rc;
+    }
+
+    /* Verify the address is unicast. */
+    if (   ((Net6.au8[0] & 0xe0) != 0x20)  /* global 2000::/3 */
+        && ((Net6.au8[0] & 0xfe) != 0xfc)) /* local  fc00::/7 */
+    {
+        reportError("IPv6 prefix %RTnaipv6 is not unicast.\n", &Net6);
+        return VERR_INVALID_PARAMETER;
+    }
+
+    /* Verify the interfaces ID part is zero */
+    if (Net6.au64[1] != 0)
+    {
+        reportError("Non-zero bits in the interface ID part"
+                    " of the IPv6 prefix %RTnaipv6/64.\n", &Net6);
+        return VERR_INVALID_PARAMETER;
+    }
+
+    /* Use ...::1 as our address */
+    RTNETADDRIPV6 Addr6 = Net6;
+    Addr6.au8[15] = 0x01;
+    memcpy(&m_ProxyOptions.ipv6_addr, &Addr6, sizeof(ip6_addr_t));
+
+
+    /*
+     * Should we advertise ourselves as default IPv6 route?  If the
+     * host doesn't have IPv6 connectivity, it's probably better not
+     * to, to prevent the guest from IPv6 connection attempts doomed
+     * to fail.
+     *
+     * We might want to make this modifiable while the natnet is
+     * running.
+     */
+    BOOL fIPv6DefaultRoute = FALSE;
+    hrc = m_net->COMGETTER(AdvertiseDefaultIPv6RouteEnabled)(&fIPv6DefaultRoute);
+    if (FAILED(hrc))
+    {
+        reportComError(m_net, "AdvertiseDefaultIPv6RouteEnabled", hrc);
+        return VERR_GENERAL_FAILURE;
+    }
+
+    m_ProxyOptions.ipv6_defroute = fIPv6DefaultRoute;
+
+
+    /* Raw socket for ICMP. */
+    initIPv6RawSock();
+
+
+    /* IPv6 source address, if configured. */
+    com::Utf8Str strSourceIp6;
+    rc = getExtraData(strSourceIp6, "SourceIp6");
+    if (RT_SUCCESS(rc) && strSourceIp6.isNotEmpty())
+    {
+        RTNETADDRIPV6 addr;
+        char *pszZone = NULL;
+        rc = RTNetStrToIPv6Addr(strSourceIp6.c_str(), &addr, &pszZone);
+        if (RT_SUCCESS(rc))
+        {
+            memcpy(&m_src6.sin6_addr, &addr, sizeof(addr));
+            m_ProxyOptions.src6 = &m_src6;
+
+            LogRel(("Will use %RTnaipv6 as IPv6 source address\n",
+                    &m_src6.sin6_addr));
+        }
+        else
+        {
+            LogRel(("Failed to parse \"%s\" IPv6 source address specification\n",
+                    strSourceIp6.c_str()));
+        }
+    }
+
+    return VINF_SUCCESS;
+}
+
+
+/**
+ * Create raw IPv6 socket for sending and snooping ICMP6.
+ */
+void VBoxNetLwipNAT::initIPv6RawSock()
+{
+    SOCKET icmpsock6 = INVALID_SOCKET;
+
+#ifndef RT_OS_DARWIN
+    const int icmpstype = SOCK_RAW;
+#else
+    /* on OS X it's not privileged */
+    const int icmpstype = SOCK_DGRAM;
+#endif
+
+    icmpsock6 = socket(AF_INET6, icmpstype, IPPROTO_ICMPV6);
+    if (icmpsock6 == INVALID_SOCKET)
+    {
+        perror("IPPROTO_ICMPV6");
+#ifdef VBOX_RAWSOCK_DEBUG_HELPER
+        icmpsock6 = getrawsock(AF_INET6);
+#endif
+    }
+
+    if (icmpsock6 != INVALID_SOCKET)
+    {
+#ifdef ICMP6_FILTER             // Windows doesn't support RFC 3542 API
+        /*
+         * XXX: We do this here for now, not in pxping.c, to avoid
+         * name clashes between lwIP and system headers.
+         */
+        struct icmp6_filter flt;
+        ICMP6_FILTER_SETBLOCKALL(&flt);
+
+        ICMP6_FILTER_SETPASS(ICMP6_ECHO_REPLY, &flt);
+
+        ICMP6_FILTER_SETPASS(ICMP6_DST_UNREACH, &flt);
+        ICMP6_FILTER_SETPASS(ICMP6_PACKET_TOO_BIG, &flt);
+        ICMP6_FILTER_SETPASS(ICMP6_TIME_EXCEEDED, &flt);
+        ICMP6_FILTER_SETPASS(ICMP6_PARAM_PROB, &flt);
+
+        int status = setsockopt(icmpsock6, IPPROTO_ICMPV6, ICMP6_FILTER,
+                                &flt, sizeof(flt));
+        if (status < 0)
+        {
+            perror("ICMP6_FILTER");
+        }
+#endif
+    }
+
+    m_ProxyOptions.icmpsock6 = icmpsock6;
+}
+
+
+
+/**
+ * Adapter for the ListenerImpl template.  It has to be a separate
+ * object because ListenerImpl deletes it.  Just a small wrapper that
+ * delegates the real work back to VBoxNetLwipNAT.
+ */
+class VBoxNetLwipNAT::Listener::Adapter
+{
+    VBoxNetLwipNAT *m_pNAT;
+public:
+    Adapter() : m_pNAT(NULL) {}
+    HRESULT init() { return init(NULL); }
+    void uninit() { m_pNAT = NULL; }
+
+    HRESULT init(VBoxNetLwipNAT *pNAT)
+    {
+        m_pNAT = pNAT;
+        return S_OK;
+    }
+
+    HRESULT HandleEvent(VBoxEventType_T aEventType, IEvent *pEvent)
+    {
+        if (RT_LIKELY(m_pNAT != NULL))
+            return m_pNAT->HandleEvent(aEventType, pEvent);
+        else
+            return S_OK;
+    }
+};
+
+
+HRESULT
+VBoxNetLwipNAT::Listener::init(VBoxNetLwipNAT *pNAT)
+{
+    HRESULT hrc;
+
+    hrc = m_pListenerImpl.createObject();
+    if (FAILED(hrc))
+        return hrc;
+
+    hrc = m_pListenerImpl->init(new Adapter(), pNAT);
+    if (FAILED(hrc))
+    {
+        VBoxNetLwipNAT::reportComError(m_pListenerImpl, "init", hrc);
+        return hrc;
+    }
+
+    return hrc;
+}
+
+
+void
+VBoxNetLwipNAT::Listener::uninit()
+{
+    unlisten();
+    m_pListenerImpl.setNull();
+}
+
+
+/*
+ * There's no base interface that exposes "eventSource" so fake it
+ * with a template.
+ */
+template <typename IEventful>
+HRESULT
+VBoxNetLwipNAT::Listener::listen(const ComPtr<IEventful> &pEventful,
+                                         const VBoxEventType_T aEvents[])
+{
+    HRESULT hrc;
+
+    if (m_pListenerImpl.isNull())
+        return S_OK;
+
+    ComPtr<IEventSource> pEventSource;
+    hrc = pEventful->COMGETTER(EventSource)(pEventSource.asOutParam());
+    if (FAILED(hrc))
+    {
+        VBoxNetLwipNAT::reportComError(pEventful, "EventSource", hrc);
+        return hrc;
+    }
+
+    /* got a real interface, punt to the non-template code */
+    hrc = doListen(pEventSource, aEvents);
+    if (FAILED(hrc))
+        return hrc;
+
+    return hrc;
+}
+
+
+HRESULT
+VBoxNetLwipNAT::Listener::doListen(const ComPtr<IEventSource> &pEventSource,
+                                   const VBoxEventType_T aEvents[])
+{
+    HRESULT hrc;
+
+    com::SafeArray<VBoxEventType_T> aInteresting;
+    for (size_t i = 0; aEvents[i] != VBoxEventType_Invalid; ++i)
+        aInteresting.push_back(aEvents[i]);
+
+    BOOL fActive = true;
+    hrc = pEventSource->RegisterListener(m_pListenerImpl,
+                                         ComSafeArrayAsInParam(aInteresting),
+                                         fActive);
+    if (FAILED(hrc))
+    {
+        VBoxNetLwipNAT::reportComError(m_pEventSource, "RegisterListener", hrc);
+        return hrc;
+    }
+
+    m_pEventSource = pEventSource;
+    return hrc;
+}
+
+
+HRESULT
+VBoxNetLwipNAT::Listener::unlisten()
+{
+    HRESULT hrc;
+
+    if (m_pEventSource.isNull())
+        return S_OK;
+
+    const ComPtr<IEventSource> pEventSource = m_pEventSource;
+    m_pEventSource.setNull();
+
+    hrc = pEventSource->UnregisterListener(m_pListenerImpl);
+    if (FAILED(hrc))
+    {
+        VBoxNetLwipNAT::reportComError(pEventSource, "UnregisterListener", hrc);
+        return hrc;
+    }
+
+    return hrc;
+}
+
+
+
+/**
+ * Create and register API event listeners.
+ */
+int VBoxNetLwipNAT::initComEvents()
+{
+    /**
+     * @todo r=uwe These events are reported on both IVirtualBox and
+     * INATNetwork objects.  We used to listen for them on our
+     * network, but it was changed later to listen on vbox.  Leave it
+     * that way for now.  Note that HandleEvent() has to do additional
+     * check for them to ignore events for other networks.
+     */
+    static const VBoxEventType_T s_aNATNetEvents[] = {
+        VBoxEventType_OnNATNetworkPortForward,
+        VBoxEventType_OnNATNetworkSetting,
+        VBoxEventType_Invalid
+    };
+    m_ListenerNATNet.init(this);
+    m_ListenerNATNet.listen(virtualbox, s_aNATNetEvents); // sic!
+
+    static const VBoxEventType_T s_aVirtualBoxEvents[] = {
+        VBoxEventType_OnHostNameResolutionConfigurationChange,
+        VBoxEventType_OnNATNetworkStartStop,
+        VBoxEventType_Invalid
+    };
+    m_ListenerVirtualBox.init(this);
+    m_ListenerVirtualBox.listen(virtualbox, s_aVirtualBoxEvents);
+
+    static const VBoxEventType_T s_aVBoxClientEvents[] = {
+        VBoxEventType_OnVBoxSVCAvailabilityChanged,
+        VBoxEventType_Invalid
+    };
+    m_ListenerVBoxClient.init(this);
+    m_ListenerVBoxClient.listen(virtualboxClient, s_aVBoxClientEvents);
+
+    return VINF_SUCCESS;
+}
+
+
+/**
+ * Perform lwIP initialization on the lwIP "tcpip" thread.
+ *
+ * The lwIP thread was created in init() and this function is run
+ * before the main lwIP loop is started.  It is responsible for
+ * setting up lwIP state, configuring interface(s), etc.
+ a*/
+/*static*/
+DECLCALLBACK(void) VBoxNetLwipNAT::onLwipTcpIpInit(void *arg)
+{
+    AssertPtrReturnVoid(arg);
+    VBoxNetLwipNAT *self = static_cast<VBoxNetLwipNAT *>(arg);
+
+    HRESULT hrc = com::Initialize();
+    AssertComRCReturnVoid(hrc);
+
+    proxy_arp_hook = pxremap_proxy_arp;
+    proxy_ip4_divert_hook = pxremap_ip4_divert;
+
+    proxy_na_hook = pxremap_proxy_na;
+    proxy_ip6_divert_hook = pxremap_ip6_divert;
+
+    netif *pNetif = netif_add(&self->m_LwipNetIf /* Lwip Interface */,
+                              &self->m_ProxyOptions.ipv4_addr, /* IP address*/
+                              &self->m_ProxyOptions.ipv4_mask, /* Network mask */
+                              &self->m_ProxyOptions.ipv4_addr, /* XXX: Gateway address */
+                              self /* state */,
+                              VBoxNetLwipNAT::netifInit /* netif_init_fn */,
+                              tcpip_input /* netif_input_fn */);
+
+    AssertPtrReturnVoid(pNetif);
+
+    LogRel(("netif %c%c%d: mac %RTmac\n",
+            pNetif->name[0], pNetif->name[1], pNetif->num,
+            pNetif->hwaddr));
+    LogRel(("netif %c%c%d: inet %RTnaipv4 netmask %RTnaipv4\n",
+            pNetif->name[0], pNetif->name[1], pNetif->num,
+            pNetif->ip_addr, pNetif->netmask));
+    for (int i = 0; i < LWIP_IPV6_NUM_ADDRESSES; ++i) {
+        if (!ip6_addr_isinvalid(netif_ip6_addr_state(pNetif, i))) {
+            LogRel(("netif %c%c%d: inet6 %RTnaipv6\n",
+                    pNetif->name[0], pNetif->name[1], pNetif->num,
+                    netif_ip6_addr(pNetif, i)));
+        }
+    }
+
+    netif_set_up(pNetif);
+    netif_set_link_up(pNetif);
+
+    if (self->m_ProxyOptions.ipv6_enabled) {
+        /*
+         * XXX: lwIP currently only ever calls mld6_joingroup() in
+         * nd6_tmr() for fresh tentative addresses, which is a wrong place
+         * to do it - but I'm not keen on fixing this properly for now
+         * (with correct handling of interface up and down transitions,
+         * etc).  So stick it here as a kludge.
+         */
+        for (int i = 0; i <= 1; ++i) {
+            ip6_addr_t *paddr = netif_ip6_addr(pNetif, i);
+
+            ip6_addr_t solicited_node_multicast_address;
+            ip6_addr_set_solicitednode(&solicited_node_multicast_address,
+                                       paddr->addr[3]);
+            mld6_joingroup(paddr, &solicited_node_multicast_address);
+        }
+
+        /*
+         * XXX: We must join the solicited-node multicast for the
+         * addresses we do IPv6 NA-proxy for.  We map IPv6 loopback to
+         * proxy address + 1.  We only need the low 24 bits, and those are
+         * fixed.
+         */
+        {
+            ip6_addr_t solicited_node_multicast_address;
+
+            ip6_addr_set_solicitednode(&solicited_node_multicast_address,
+                                       /* last 24 bits of the address */
+                                       PP_HTONL(0x00000002));
+            mld6_netif_joingroup(pNetif,  &solicited_node_multicast_address);
+        }
+    }
+
+    proxy_init(&self->m_LwipNetIf, &self->m_ProxyOptions);
+
+    natServiceProcessRegisteredPf(self->m_vecPortForwardRule4);
+    natServiceProcessRegisteredPf(self->m_vecPortForwardRule6);
+}
+
+
+/**
+ * lwIP's callback to configure the interface.
+ *
+ * Called from onLwipTcpIpInit() via netif_add().  Called after the
+ * initerface is mostly initialized, and its IPv4 address is already
+ * configured.  Here we still need to configure the MAC address and
+ * IPv6 addresses.  It's best to consult the source of netif_add() for
+ * the exact details.
+ */
+/* static */ DECLCALLBACK(err_t)
+VBoxNetLwipNAT::netifInit(netif *pNetif) RT_NOTHROW_DEF
+{
+    err_t rcLwip = ERR_OK;
+
+    AssertPtrReturn(pNetif, ERR_ARG);
+
+    VBoxNetLwipNAT *self = static_cast<VBoxNetLwipNAT *>(pNetif->state);
+    AssertPtrReturn(self, ERR_ARG);
+
+    LogFlowFunc(("ENTER: pNetif[%c%c%d]\n", pNetif->name[0], pNetif->name[1], pNetif->num));
+    /* validity */
+    AssertReturn(   pNetif->name[0] == 'N'
+                 && pNetif->name[1] == 'T', ERR_ARG);
+
+
+    pNetif->hwaddr_len = sizeof(RTMAC);
+    memcpy(pNetif->hwaddr, &self->m_MacAddress, sizeof(RTMAC));
+
+    self->m_u16Mtu = 1500; // XXX: FIXME
+    pNetif->mtu = self->m_u16Mtu;
+
+    pNetif->flags = NETIF_FLAG_BROADCAST
+      | NETIF_FLAG_ETHARP                /* Don't bother driver with ARP and let Lwip resolve ARP handling */
+      | NETIF_FLAG_ETHERNET;             /* Lwip works with ethernet too */
+
+    pNetif->linkoutput = netifLinkoutput; /* ether-level-pipe */
+    pNetif->output = etharp_output;       /* ip-pipe */
+
+    if (self->m_ProxyOptions.ipv6_enabled) {
+        pNetif->output_ip6 = ethip6_output;
+
+        /* IPv6 link-local address in slot 0 */
+        netif_create_ip6_linklocal_address(pNetif, /* :from_mac_48bit */ 1);
+        netif_ip6_addr_set_state(pNetif, 0, IP6_ADDR_PREFERRED); // skip DAD
+
+        /* INATNetwork::IPv6Prefix in slot 1 */
+        memcpy(netif_ip6_addr(pNetif, 1),
+               &self->m_ProxyOptions.ipv6_addr, sizeof(ip6_addr_t));
+        netif_ip6_addr_set_state(pNetif, 1, IP6_ADDR_PREFERRED);
+
+#if LWIP_IPV6_SEND_ROUTER_SOLICIT
+        pNetif->rs_count = 0;
+#endif
+    }
+
+    LogFlowFunc(("LEAVE: %d\n", rcLwip));
+    return rcLwip;
+}
+
+
+/**
+ * Run the pumps.
+ *
+ * Spawn the intnet pump thread that gets packets from the intnet and
+ * feeds them to lwIP.  Enter COM event loop here, on the main thread.
+ */
+int
+VBoxNetLwipNAT::run()
+{
+    int rc;
+
+    AssertReturn(m_hThrRecv == NIL_RTTHREAD, VERR_INVALID_STATE);
+
+    /* spawn the lwIP tcpip thread */
+    vboxLwipCoreInitialize(VBoxNetLwipNAT::onLwipTcpIpInit, this);
+
+    /* spawn intnet input pump */
+    rc = RTThreadCreate(&m_hThrRecv,
+             VBoxNetLwipNAT::receiveThread, this,
+             0, /* :cbStack */
+             RTTHREADTYPE_IO, RTTHREADFLAGS_WAITABLE,
+             "RECV");
+    AssertRCReturn(rc, rc);
+
+    /* main thread will run the API event queue pump */
+    com::NativeEventQueue *pQueue = com::NativeEventQueue::getMainEventQueue();
+    if (pQueue == NULL)
+    {
+        LogRel(("run: getMainEventQueue() == NULL\n"));
+        return VERR_GENERAL_FAILURE;
+    }
+
+    /* dispatch API events to our listeners */
+    for (;;)
+    {
+        rc = pQueue->processEventQueue(RT_INDEFINITE_WAIT);
+        if (rc == VERR_INTERRUPTED)
+        {
+            LogRel(("run: shutdown\n"));
+            break;
+        }
+        else if (rc != VINF_SUCCESS)
+        {
+            /* note any unexpected rc */
+            LogRel(("run: processEventQueue: %Rrc\n", rc));
+        }
+    }
+
+    /*
+     * We are out of the event loop, so we were told to shut down.
+     * Tell other threads to wrap up.
+     */
+
+    /* tell the intnet input pump to terminate */
+    IntNetR3IfWaitAbort(m_hIf);
+
+    /* tell the lwIP tcpip thread to terminate */
+    vboxLwipCoreFinalize(VBoxNetLwipNAT::onLwipTcpIpFini, this);
+
+    rc = RTThreadWait(m_hThrRecv, 5000, NULL);
+    m_hThrRecv = NIL_RTTHREAD;
+
+    return VINF_SUCCESS;
+}
+
+
+void
+VBoxNetLwipNAT::shutdown()
+{
+    int rc;
+
+    com::NativeEventQueue *pQueue = com::NativeEventQueue::getMainEventQueue();
+    if (pQueue == NULL)
+    {
+        LogRel(("shutdown: getMainEventQueue() == NULL\n"));
+        return;
+    }
+
+    /* unregister listeners */
+    m_ListenerNATNet.unlisten();
+    m_ListenerVirtualBox.unlisten();
+    m_ListenerVBoxClient.unlisten();
+
+    /* tell the event loop in run() to stop */
+    rc = pQueue->interruptEventQueueProcessing();
+    if (RT_FAILURE(rc))
+        LogRel(("shutdown: interruptEventQueueProcessing: %Rrc\n", rc));
+}
+
+
+/**
+ * Run finalization on the lwIP "tcpip" thread.
+ */
+/* static */
+DECLCALLBACK(void) VBoxNetLwipNAT::onLwipTcpIpFini(void *arg)
+{
+    AssertPtrReturnVoid(arg);
+    VBoxNetLwipNAT *self = static_cast<VBoxNetLwipNAT *>(arg);
+
+    /* XXX: proxy finalization */
+    netif_set_link_down(&self->m_LwipNetIf);
+    netif_set_down(&self->m_LwipNetIf);
+    netif_remove(&self->m_LwipNetIf);
+}
+
+
+/**
+ * @note: this work on Event thread.
+ */
+HRESULT VBoxNetLwipNAT::HandleEvent(VBoxEventType_T aEventType, IEvent *pEvent)
+{
+    HRESULT hrc = S_OK;
+    switch (aEventType)
+    {
+        case VBoxEventType_OnNATNetworkSetting:
+        {
+            ComPtr<INATNetworkSettingEvent> pSettingsEvent(pEvent);
+
+            com::Bstr networkName;
+            hrc = pSettingsEvent->COMGETTER(NetworkName)(networkName.asOutParam());
+            AssertComRCReturn(hrc, hrc);
+            if (networkName != m_strNetworkName)
+                break; /* change not for our network */
+
+            // XXX: only handle IPv6 default route for now
+            if (!m_ProxyOptions.ipv6_enabled)
+                break;
+
+            BOOL fIPv6DefaultRoute = FALSE;
+            hrc = pSettingsEvent->COMGETTER(AdvertiseDefaultIPv6RouteEnabled)(&fIPv6DefaultRoute);
+            AssertComRCReturn(hrc, hrc);
+
+            if (m_ProxyOptions.ipv6_defroute == fIPv6DefaultRoute)
+                break;
+
+            m_ProxyOptions.ipv6_defroute = fIPv6DefaultRoute;
+            tcpip_callback_with_block(proxy_rtadvd_do_quick, &m_LwipNetIf, 0);
+            break;
+        }
+
+        case VBoxEventType_OnNATNetworkPortForward:
+        {
+            ComPtr<INATNetworkPortForwardEvent> pForwardEvent = pEvent;
+
+            com::Bstr networkName;
+            hrc = pForwardEvent->COMGETTER(NetworkName)(networkName.asOutParam());
+            AssertComRCReturn(hrc, hrc);
+            if (networkName != m_strNetworkName)
+                break; /* change not for our network */
+
+            BOOL fCreateFW;
+            hrc = pForwardEvent->COMGETTER(Create)(&fCreateFW);
+            AssertComRCReturn(hrc, hrc);
+
+            BOOL  fIPv6FW;
+            hrc = pForwardEvent->COMGETTER(Ipv6)(&fIPv6FW);
+            AssertComRCReturn(hrc, hrc);
+
+            com::Bstr name;
+            hrc = pForwardEvent->COMGETTER(Name)(name.asOutParam());
+            AssertComRCReturn(hrc, hrc);
+
+            NATProtocol_T proto = NATProtocol_TCP;
+            hrc = pForwardEvent->COMGETTER(Proto)(&proto);
+            AssertComRCReturn(hrc, hrc);
+
+            com::Bstr strHostAddr;
+            hrc = pForwardEvent->COMGETTER(HostIp)(strHostAddr.asOutParam());
+            AssertComRCReturn(hrc, hrc);
+
+            LONG lHostPort;
+            hrc = pForwardEvent->COMGETTER(HostPort)(&lHostPort);
+            AssertComRCReturn(hrc, hrc);
+
+            com::Bstr strGuestAddr;
+            hrc = pForwardEvent->COMGETTER(GuestIp)(strGuestAddr.asOutParam());
+            AssertComRCReturn(hrc, hrc);
+
+            LONG lGuestPort;
+            hrc = pForwardEvent->COMGETTER(GuestPort)(&lGuestPort);
+            AssertComRCReturn(hrc, hrc);
+
+            VECNATSERVICEPF& rules = fIPv6FW ? m_vecPortForwardRule6
+                                             : m_vecPortForwardRule4;
+
+            NATSERVICEPORTFORWARDRULE r;
+            RT_ZERO(r);
+
+            r.Pfr.fPfrIPv6 = fIPv6FW;
+
+            switch (proto)
+            {
+                case NATProtocol_TCP:
+                    r.Pfr.iPfrProto = IPPROTO_TCP;
+                    break;
+                case NATProtocol_UDP:
+                    r.Pfr.iPfrProto = IPPROTO_UDP;
+                    break;
+
+                default:
+                    LogRel(("Event: %s %s port-forwarding rule \"%s\": invalid protocol %d\n",
+                            fCreateFW ? "Add" : "Remove",
+                            fIPv6FW ? "IPv6" : "IPv4",
+                            com::Utf8Str(name).c_str(),
+                            (int)proto));
+                    goto port_forward_done;
+            }
+
+            LogRel(("Event: %s %s port-forwarding rule \"%s\": %s %s%s%s:%d -> %s%s%s:%d\n",
+                    fCreateFW ? "Add" : "Remove",
+                    fIPv6FW ? "IPv6" : "IPv4",
+                    com::Utf8Str(name).c_str(),
+                    proto == NATProtocol_TCP ? "TCP" : "UDP",
+                    /* from */
+                    fIPv6FW ? "[" : "",
+                    com::Utf8Str(strHostAddr).c_str(),
+                    fIPv6FW ? "]" : "",
+                    lHostPort,
+                    /* to */
+                    fIPv6FW ? "[" : "",
+                    com::Utf8Str(strGuestAddr).c_str(),
+                    fIPv6FW ? "]" : "",
+                    lGuestPort));
+
+            if (name.length() > sizeof(r.Pfr.szPfrName))
+            {
+                hrc = E_INVALIDARG;
+                goto port_forward_done;
+            }
+
+            RTStrPrintf(r.Pfr.szPfrName, sizeof(r.Pfr.szPfrName),
+                        "%s", com::Utf8Str(name).c_str());
+
+            RTStrPrintf(r.Pfr.szPfrHostAddr, sizeof(r.Pfr.szPfrHostAddr),
+                        "%s", com::Utf8Str(strHostAddr).c_str());
+
+            /* XXX: limits should be checked */
+            r.Pfr.u16PfrHostPort = (uint16_t)lHostPort;
+
+            RTStrPrintf(r.Pfr.szPfrGuestAddr, sizeof(r.Pfr.szPfrGuestAddr),
+                        "%s", com::Utf8Str(strGuestAddr).c_str());
+
+            /* XXX: limits should be checked */
+            r.Pfr.u16PfrGuestPort = (uint16_t)lGuestPort;
+
+            if (fCreateFW) /* Addition */
+            {
+                int rc = natServicePfRegister(r);
+                if (RT_SUCCESS(rc))
+                    rules.push_back(r);
+            }
+            else /* Deletion */
+            {
+                ITERATORNATSERVICEPF it;
+                for (it = rules.begin(); it != rules.end(); ++it)
+                {
+                    /* compare */
+                    NATSERVICEPORTFORWARDRULE &natFw = *it;
+                    if (   natFw.Pfr.iPfrProto == r.Pfr.iPfrProto
+                        && natFw.Pfr.u16PfrHostPort == r.Pfr.u16PfrHostPort
+                        && strncmp(natFw.Pfr.szPfrHostAddr, r.Pfr.szPfrHostAddr, INET6_ADDRSTRLEN) == 0
+                        && natFw.Pfr.u16PfrGuestPort == r.Pfr.u16PfrGuestPort
+                        && strncmp(natFw.Pfr.szPfrGuestAddr, r.Pfr.szPfrGuestAddr, INET6_ADDRSTRLEN) == 0)
+                    {
+                        fwspec *pFwCopy = (fwspec *)RTMemDup(&natFw.FWSpec, sizeof(natFw.FWSpec));
+                        if (pFwCopy)
+                        {
+                            int status = portfwd_rule_del(pFwCopy);
+                            if (status == 0)
+                                rules.erase(it);   /* (pFwCopy is owned by lwip thread now.) */
+                            else
+                                RTMemFree(pFwCopy);
+                        }
+                        break;
+                    }
+                } /* loop over vector elements */
+            } /* condition add or delete */
+        port_forward_done:
+            /* clean up strings */
+            name.setNull();
+            strHostAddr.setNull();
+            strGuestAddr.setNull();
+            break;
+        }
+
+        case VBoxEventType_OnHostNameResolutionConfigurationChange:
+        {
+            const char **ppcszNameServers = getHostNameservers();
+            err_t error;
+
+            error = tcpip_callback_with_block(pxdns_set_nameservers,
+                                              ppcszNameServers,
+                                              /* :block */ 0);
+            if (error != ERR_OK && ppcszNameServers != NULL)
+                RTMemFree(ppcszNameServers);
+            break;
+        }
+
+        case VBoxEventType_OnNATNetworkStartStop:
+        {
+            ComPtr <INATNetworkStartStopEvent> pStartStopEvent = pEvent;
+
+            com::Bstr networkName;
+            hrc = pStartStopEvent->COMGETTER(NetworkName)(networkName.asOutParam());
+            AssertComRCReturn(hrc, hrc);
+            if (networkName != m_strNetworkName)
+                break; /* change not for our network */
+
+            BOOL fStart = TRUE;
+            hrc = pStartStopEvent->COMGETTER(StartEvent)(&fStart);
+            AssertComRCReturn(hrc, hrc);
+
+            if (!fStart)
+                shutdown();
+            break;
+        }
+
+        case VBoxEventType_OnVBoxSVCAvailabilityChanged:
+        {
+            LogRel(("VBoxSVC became unavailable, exiting.\n"));
+            shutdown();
+            break;
+        }
+
+        default: break; /* Shut up MSC. */
+    }
+    return hrc;
+}
+
+
+/**
+ * Read the list of host's resolvers via the API.
+ *
+ * Called during initialization and in response to the
+ * VBoxEventType_OnHostNameResolutionConfigurationChange event.
+ */
+const char **VBoxNetLwipNAT::getHostNameservers()
+{
+    if (m_host.isNull())
+        return NULL;
+
+    com::SafeArray<BSTR> aNameServers;
+    HRESULT hrc = m_host->COMGETTER(NameServers)(ComSafeArrayAsOutParam(aNameServers));
+    if (FAILED(hrc))
+        return NULL;
+
+    const size_t cNameServers = aNameServers.size();
+    if (cNameServers == 0)
+        return NULL;
+
+    const char **ppcszNameServers =
+        (const char **)RTMemAllocZ(sizeof(char *) * (cNameServers + 1));
+    if (ppcszNameServers == NULL)
+        return NULL;
+
+    size_t idxLast = 0;
+    for (size_t i = 0; i < cNameServers; ++i)
+    {
+        com::Utf8Str strNameServer(aNameServers[i]);
+        ppcszNameServers[idxLast] = RTStrDup(strNameServer.c_str());
+        if (ppcszNameServers[idxLast] != NULL)
+            ++idxLast;
+    }
+
+    if (idxLast == 0)
+    {
+        RTMemFree(ppcszNameServers);
+        return NULL;
+    }
+
+    return ppcszNameServers;
+}
+
+
+/**
+ * Fetch port-forwarding rules via the API.
+ *
+ * Reads the initial sets of rules from VBoxSVC.  The rules will be
+ * activated when all the initialization and plumbing is done.  See
+ * natServiceProcessRegisteredPf().
+ */
+int VBoxNetLwipNAT::fetchNatPortForwardRules(VECNATSERVICEPF &vec, bool fIsIPv6)
+{
+    HRESULT hrc;
+
+    com::SafeArray<BSTR> rules;
+    if (fIsIPv6)
+        hrc = m_net->COMGETTER(PortForwardRules6)(ComSafeArrayAsOutParam(rules));
+    else
+        hrc = m_net->COMGETTER(PortForwardRules4)(ComSafeArrayAsOutParam(rules));
+    AssertComRCReturn(hrc, VERR_INTERNAL_ERROR);
+
+    NATSERVICEPORTFORWARDRULE Rule;
+    for (size_t idxRules = 0; idxRules < rules.size(); ++idxRules)
+    {
+        Log(("%d-%s rule: %ls\n", idxRules, (fIsIPv6 ? "IPv6" : "IPv4"), rules[idxRules]));
+        RT_ZERO(Rule);
+
+        int rc = netPfStrToPf(com::Utf8Str(rules[idxRules]).c_str(), fIsIPv6,
+                              &Rule.Pfr);
+        if (RT_FAILURE(rc))
+            continue;
+
+        vec.push_back(Rule);
+    }
+
+    return VINF_SUCCESS;
+}
+
+
+/**
+ * Activate the initial set of port-forwarding rules.
+ *
+ * Happens after lwIP and lwIP proxy is initialized, right before lwIP
+ * thread starts processing messages.
+ */
+/* static */
+int VBoxNetLwipNAT::natServiceProcessRegisteredPf(VECNATSERVICEPF& vecRules)
+{
+    ITERATORNATSERVICEPF it;
+    for (it = vecRules.begin(); it != vecRules.end(); ++it)
+    {
+        NATSERVICEPORTFORWARDRULE &natPf = *it;
+
+        LogRel(("Loading %s port-forwarding rule \"%s\": %s %s%s%s:%d -> %s%s%s:%d\n",
+                natPf.Pfr.fPfrIPv6 ? "IPv6" : "IPv4",
+                natPf.Pfr.szPfrName,
+                natPf.Pfr.iPfrProto == IPPROTO_TCP ? "TCP" : "UDP",
+                /* from */
+                natPf.Pfr.fPfrIPv6 ? "[" : "",
+                natPf.Pfr.szPfrHostAddr,
+                natPf.Pfr.fPfrIPv6 ? "]" : "",
+                natPf.Pfr.u16PfrHostPort,
+                /* to */
+                natPf.Pfr.fPfrIPv6 ? "[" : "",
+                natPf.Pfr.szPfrGuestAddr,
+                natPf.Pfr.fPfrIPv6 ? "]" : "",
+                natPf.Pfr.u16PfrGuestPort));
+
+        natServicePfRegister(natPf);
+    }
+
+    return VINF_SUCCESS;
+}
+
+
+/**
+ * Activate a single port-forwarding rule.
+ *
+ * This is used both when we activate all the initial rules on startup
+ * and when port-forwarding rules are changed and we are notified via
+ * an API event.
+ */
+/* static */
+int VBoxNetLwipNAT::natServicePfRegister(NATSERVICEPORTFORWARDRULE &natPf)
+{
+    int lrc;
+
+    int sockFamily = (natPf.Pfr.fPfrIPv6 ? PF_INET6 : PF_INET);
+    int socketSpec;
+    switch(natPf.Pfr.iPfrProto)
+    {
+        case IPPROTO_TCP:
+            socketSpec = SOCK_STREAM;
+            break;
+        case IPPROTO_UDP:
+            socketSpec = SOCK_DGRAM;
+            break;
+        default:
+            return VERR_IGNORED;
+    }
+
+    const char *pszHostAddr = natPf.Pfr.szPfrHostAddr;
+    if (pszHostAddr[0] == '\0')
+    {
+        if (sockFamily == PF_INET)
+            pszHostAddr = "0.0.0.0";
+        else
+            pszHostAddr = "::";
+    }
+
+    lrc = fwspec_set(&natPf.FWSpec,
+                     sockFamily,
+                     socketSpec,
+                     pszHostAddr,
+                     natPf.Pfr.u16PfrHostPort,
+                     natPf.Pfr.szPfrGuestAddr,
+                     natPf.Pfr.u16PfrGuestPort);
+    if (lrc != 0)
+        return VERR_IGNORED;
+
+    fwspec *pFwCopy = (fwspec *)RTMemDup(&natPf.FWSpec, sizeof(natPf.FWSpec));
+    if (pFwCopy)
+    {
+        lrc = portfwd_rule_add(pFwCopy);
+        if (lrc == 0)
+            return VINF_SUCCESS; /* (pFwCopy is owned by lwip thread now.) */
+        RTMemFree(pFwCopy);
+    }
+    else
+        LogRel(("Unable to allocate memory for %s rule \"%s\"\n",
+                natPf.Pfr.fPfrIPv6 ? "IPv6" : "IPv4",
+                natPf.Pfr.szPfrName));
+    return VERR_IGNORED;
+}
+
+
+/**
+ * IntNetIf receive thread.  Runs intnet pump with our processFrame()
+ * as input callback.
+ */
+/* static */ DECLCALLBACK(int)
+VBoxNetLwipNAT::receiveThread(RTTHREAD hThreadSelf, void *pvUser)
+{
+    HRESULT hrc;
+    int rc;
+
+    RT_NOREF(hThreadSelf);
+
+    AssertReturn(pvUser != NULL, VERR_INVALID_PARAMETER);
+    VBoxNetLwipNAT *self = static_cast<VBoxNetLwipNAT *>(pvUser);
+
+    /* do we relaly need to init com on this thread? */
+    hrc = com::Initialize();
+    if (FAILED(hrc))
+        return VERR_GENERAL_FAILURE;
+
+    rc = IntNetR3IfPumpPkts(self->m_hIf, VBoxNetLwipNAT::processFrame, self,
+                            NULL /*pfnInputGso*/, NULL /*pvUserGso*/);
+    if (rc == VERR_SEM_DESTROYED)
+        return VINF_SUCCESS;
+
+    LogRel(("receiveThread: IntNetR3IfPumpPkts: unexpected %Rrc\n", rc));
+    return VERR_INVALID_STATE;
+}
+
+
+/**
+ * Process an incoming frame received from the intnet.
+ */
+/* static */ DECLCALLBACK(void)
+VBoxNetLwipNAT::processFrame(void *pvUser, void *pvFrame, uint32_t cbFrame)
+{
+    AssertReturnVoid(pvFrame != NULL);
+
+    /* shouldn't happen, but if it does, don't even bother */
+    if (RT_UNLIKELY(cbFrame < sizeof(RTNETETHERHDR)))
+        return;
+
+    /* we expect normal ethernet frame including .1Q and FCS */
+    if (cbFrame > 1522)
+        return;
+
+    AssertReturnVoid(pvUser != NULL);
+    VBoxNetLwipNAT *self = static_cast<VBoxNetLwipNAT *>(pvUser);
+
+    struct pbuf *p = pbuf_alloc(PBUF_RAW, (u16_t)cbFrame + ETH_PAD_SIZE, PBUF_POOL);
+    if (RT_UNLIKELY(p == NULL))
+        return;
+
+    /*
+     * The code below is inlined version of:
+     *
+     *   pbuf_header(p, -ETH_PAD_SIZE); // hide padding
+     *   pbuf_take(p, pvFrame, cbFrame);
+     *   pbuf_header(p, ETH_PAD_SIZE);  // reveal padding
+     */
+    struct pbuf *q = p;
+    uint8_t *pu8Chunk = (uint8_t *)pvFrame;
+    do {
+        uint8_t *payload = (uint8_t *)q->payload;
+        size_t len = q->len;
+
+#if ETH_PAD_SIZE
+        if (RT_LIKELY(q == p))  // single pbuf is large enough
+        {
+            payload += ETH_PAD_SIZE;
+            len -= ETH_PAD_SIZE;
+        }
+#endif
+        memcpy(payload, pu8Chunk, len);
+        pu8Chunk += len;
+        q = q->next;
+    } while (RT_UNLIKELY(q != NULL));
+
+    /* pass input to lwIP: netif input funcion tcpip_input() */
+    self->m_LwipNetIf.input(p, &self->m_LwipNetIf);
+}
+
+
+/**
+ * Send an outgoing frame from lwIP to intnet.
+ */
+/* static */ DECLCALLBACK(err_t)
+VBoxNetLwipNAT::netifLinkoutput(netif *pNetif, pbuf *pPBuf) RT_NOTHROW_DEF
+{
+    int rc;
+
+    AssertPtrReturn(pNetif, ERR_ARG);
+    AssertPtrReturn(pPBuf, ERR_ARG);
+
+    VBoxNetLwipNAT *self = static_cast<VBoxNetLwipNAT *>(pNetif->state);
+    AssertPtrReturn(self, ERR_IF);
+    AssertReturn(pNetif == &self->m_LwipNetIf, ERR_IF);
+
+    LogFlowFunc(("ENTER: pNetif[%c%c%d], pPbuf:%p\n",
+                 pNetif->name[0],
+                 pNetif->name[1],
+                 pNetif->num,
+                 pPBuf));
+
+    if (pPBuf->tot_len < sizeof(struct eth_hdr)) /* includes ETH_PAD_SIZE */
+        return ERR_ARG;
+
+    size_t cbFrame = (size_t)pPBuf->tot_len - ETH_PAD_SIZE;
+    INTNETFRAME Frame;
+    rc = IntNetR3IfQueryOutputFrame(self->m_hIf, (uint32_t)cbFrame, &Frame);
+    if (RT_FAILURE(rc))
+        return ERR_MEM;
+
+    pbuf_copy_partial(pPBuf, Frame.pvFrame, (u16_t)cbFrame, ETH_PAD_SIZE);
+    rc = IntNetR3IfOutputFrameCommit(self->m_hIf, &Frame);
+    if (RT_FAILURE(rc))
+        return ERR_IF;
+
+    LogFlowFunc(("LEAVE: %d\n", ERR_OK));
+    return ERR_OK;
+}
+
+
+/**
+ * Retrieve network-specific extra data item.
+ */
+int VBoxNetLwipNAT::getExtraData(com::Utf8Str &strValueOut, const char *pcszKey)
+{
+    HRESULT hrc;
+
+    AssertReturn(!virtualbox.isNull(), E_FAIL);
+    AssertReturn(m_strNetworkName.isNotEmpty(), E_FAIL);
+    AssertReturn(pcszKey != NULL, E_FAIL);
+    AssertReturn(*pcszKey != '\0', E_FAIL);
+
+    com::BstrFmt bstrKey("NAT/%s/%s", m_strNetworkName.c_str(), pcszKey);
+    com::Bstr bstrValue;
+    hrc = virtualbox->GetExtraData(bstrKey.raw(), bstrValue.asOutParam());
+    if (FAILED(hrc))
+    {
+        reportComError(virtualbox, "GetExtraData", hrc);
+        return VERR_GENERAL_FAILURE;
+    }
+
+    strValueOut = bstrValue;
+    return VINF_SUCCESS;
+}
+
+
+/* static */
+HRESULT VBoxNetLwipNAT::reportComError(ComPtr<IUnknown> iface,
+                                       const com::Utf8Str &strContext,
+                                       HRESULT hrc)
+{
+    const com::ErrorInfo info(iface, COM_IIDOF(IUnknown));
+    if (info.isFullAvailable() || info.isBasicAvailable())
+    {
+        reportErrorInfoList(info, strContext);
+    }
+    else
+    {
+        if (strContext.isNotEmpty())
+            reportError("%s: %Rhra", strContext.c_str(), hrc);
+        else
+            reportError("%Rhra", hrc);
+    }
+
+    return hrc;
+}
+
+
+/* static */
+void VBoxNetLwipNAT::reportErrorInfoList(const com::ErrorInfo &info,
+                                         const com::Utf8Str &strContext)
+{
+    if (strContext.isNotEmpty())
+        reportError("%s", strContext.c_str());
+
+    bool fFirst = true;
+    for (const com::ErrorInfo *pInfo = &info;
+         pInfo != NULL;
+         pInfo = pInfo->getNext())
+    {
+        if (fFirst)
+            fFirst = false;
+        else
+            reportError("--------");
+
+        reportErrorInfo(*pInfo);
+    }
+}
+
+
+/* static */
+void VBoxNetLwipNAT::reportErrorInfo(const com::ErrorInfo &info)
+{
+#if defined (RT_OS_WIN)
+    bool haveResultCode = info.isFullAvailable();
+    bool haveComponent = true;
+    bool haveInterfaceID = true;
+#else /* !RT_OS_WIN */
+    bool haveResultCode = true;
+    bool haveComponent = info.isFullAvailable();
+    bool haveInterfaceID = info.isFullAvailable();
+#endif
+    com::Utf8Str message;
+    if (info.getText().isNotEmpty())
+        message = info.getText();
+
+    const char *pcszDetails = "Details: ";
+    const char *pcszComma = ", ";
+    const char *pcszSeparator = pcszDetails;
+
+    if (haveResultCode)
+    {
+        message.appendPrintf("%s" "code %Rhrc (0x%RX32)",
+            pcszSeparator, info.getResultCode(), info.getResultCode());
+        pcszSeparator = pcszComma;
+    }
+
+    if (haveComponent)
+    {
+        message.appendPrintf("%s" "component %ls",
+            pcszSeparator, info.getComponent().raw());
+        pcszSeparator = pcszComma;
+    }
+
+    if (haveInterfaceID)
+    {
+        message.appendPrintf("%s" "interface %ls",
+            pcszSeparator, info.getInterfaceName().raw());
+        pcszSeparator = pcszComma;
+    }
+
+    if (info.getCalleeName().isNotEmpty())
+    {
+        message.appendPrintf("%s" "callee %ls",
+            pcszSeparator, info.getCalleeName().raw());
+        pcszSeparator = pcszComma;
+    }
+
+    reportError("%s", message.c_str());
+}
+
+
+/* static */
+void VBoxNetLwipNAT::reportError(const char *a_pcszFormat, ...)
+{
+    va_list ap;
+
+    va_start(ap, a_pcszFormat);
+    com::Utf8Str message(a_pcszFormat, ap);
+    va_end(ap);
+
+    RTMsgError("%s", message.c_str());
+    LogRel(("%s", message.c_str()));
+}
+
+
+
+/**
+ * Create release logger.
+ *
+ * The NAT network name is sanitized so that it can be used in a path
+ * component.  By default the release log is written to the file
+ * ~/.VirtualBox/${netname}.log but its destiation and content can be
+ * overridden with VBOXNET_${netname}_RELEASE_LOG family of
+ * environment variables (also ..._DEST and ..._FLAGS).
+ */
+/* static */
+int VBoxNetLwipNAT::initLog()
+{
+    size_t cch;
+    int rc;
+
+    if (m_strNetworkName.isEmpty())
+        return VERR_MISSING;
+
+    char szNetwork[RTPATH_MAX];
+    rc = RTStrCopy(szNetwork, sizeof(szNetwork), m_strNetworkName.c_str());
+    if (RT_FAILURE(rc))
+        return rc;
+
+    // sanitize network name to be usable as a path component
+    for (char *p = szNetwork; *p != '\0'; ++p)
+    {
+        if (RTPATH_IS_SEP(*p))
+            *p = '_';
+    }
+
+    const char *pcszLogFile = NULL;
+    char szLogFile[RTPATH_MAX];
+    if (m_strHome.isNotEmpty())
+    {
+        cch = RTStrPrintf(szLogFile, sizeof(szLogFile),
+                          "%s%c%s.log", m_strHome.c_str(), RTPATH_DELIMITER, szNetwork);
+        if (cch < sizeof(szLogFile))
+            pcszLogFile = szLogFile;
+    }
+
+    // sanitize network name some more to be usable as environment variable
+    for (char *p = szNetwork; *p != '\0'; ++p)
+    {
+        if (*p != '_'
+            && (*p < '0' || '9' < *p)
+            && (*p < 'a' || 'z' < *p)
+            && (*p < 'A' || 'Z' < *p))
+        {
+            *p = '_';
+        }
+    }
+
+    char szEnvVarBase[128];
+    const char *pcszEnvVarBase = szEnvVarBase;
+    cch = RTStrPrintf(szEnvVarBase, sizeof(szEnvVarBase),
+                      "VBOXNET_%s_RELEASE_LOG", szNetwork);
+    if (cch >= sizeof(szEnvVarBase))
+        pcszEnvVarBase = NULL;
+
+    rc = com::VBoxLogRelCreate("NAT Network",
+                               pcszLogFile,
+                               RTLOGFLAGS_PREFIX_TIME_PROG,
+                               "all all.restrict -default.restrict",
+                               pcszEnvVarBase,
+                               RTLOGDEST_FILE,
+                               32768 /* cMaxEntriesPerGroup */,
+                               0 /* cHistory */,
+                               0 /* uHistoryFileTime */,
+                               0 /* uHistoryFileSize */,
+                               NULL /*pErrInfo*/);
+
+    /*
+     * Provide immediate feedback if corresponding LogRel level is
+     * enabled.  It's frustrating when you chase some rare event and
+     * discover you didn't actually have the corresponding log level
+     * enabled because of a typo in the environment variable name or
+     * its content.
+     */
+#define LOG_PING(_log) _log((#_log " enabled\n"))
+    LOG_PING(LogRel2);
+    LOG_PING(LogRel3);
+    LOG_PING(LogRel4);
+    LOG_PING(LogRel5);
+    LOG_PING(LogRel6);
+    LOG_PING(LogRel7);
+    LOG_PING(LogRel8);
+    LOG_PING(LogRel9);
+    LOG_PING(LogRel10);
+    LOG_PING(LogRel11);
+    LOG_PING(LogRel12);
+
+    return rc;
+}
+
+
+/**
+ *  Entry point.
+ */
+extern "C" DECLEXPORT(int) TrustedMain(int argc, char **argv, char **envp)
+{
+    LogFlowFuncEnter();
+    NOREF(envp);
+
+#ifdef RT_OS_WINDOWS
+    WSADATA WsaData = {0};
+    int err = WSAStartup(MAKEWORD(2,2), &WsaData);
+    if (err)
+    {
+        fprintf(stderr, "wsastartup: failed (%d)\n", err);
+        return RTEXITCODE_INIT;
+    }
+#endif
+
+    VBoxNetLwipNAT NAT;
+
+    int rcExit = NAT.parseArgs(argc, argv);
+    if (rcExit != RTEXITCODE_SUCCESS)
+    {
+        /* messages are already printed */
+        return rcExit == RTEXITCODE_DONE ? RTEXITCODE_SUCCESS : rcExit;
+    }
+
+    int rc = NAT.init();
+    if (RT_FAILURE(rc))
+        return RTEXITCODE_INIT;
+
+    NAT.run();
+
+    LogRel(("Terminating\n"));
+    return RTEXITCODE_SUCCESS;
+}
+
+
+#ifndef VBOX_WITH_HARDENING
+
+int main(int argc, char **argv, char **envp)
+{
+    int rc = RTR3InitExe(argc, &argv, RTR3INIT_FLAGS_SUPLIB);
+    if (RT_SUCCESS(rc))
+        return TrustedMain(argc, argv, envp);
+    return RTMsgInitFailure(rc);
+}
+
+# if defined(RT_OS_WINDOWS)
+
+#  if 0 /* Some copy and paste from DHCP that nobody explained why was diabled. */
+static LRESULT CALLBACK WindowProc(HWND hwnd,
+    UINT uMsg,
+    WPARAM wParam,
+    LPARAM lParam
+)
+{
+    if(uMsg == WM_DESTROY)
+    {
+        PostQuitMessage(0);
+        return 0;
+    }
+    return DefWindowProc (hwnd, uMsg, wParam, lParam);
+}
+
+static LPCWSTR g_WndClassName = L"VBoxNetNatLwipClass";
+
+static DWORD WINAPI MsgThreadProc(__in  LPVOID lpParameter)
+{
+     HWND                 hwnd = 0;
+     HINSTANCE hInstance = (HINSTANCE)GetModuleHandle (NULL);
+     bool bExit = false;
+
+     /* Register the Window Class. */
+     WNDCLASS wc;
+     wc.style         = 0;
+     wc.lpfnWndProc   = WindowProc;
+     wc.cbClsExtra    = 0;
+     wc.cbWndExtra    = sizeof(void *);
+     wc.hInstance     = hInstance;
+     wc.hIcon         = NULL;
+     wc.hCursor       = NULL;
+     wc.hbrBackground = (HBRUSH)(COLOR_BACKGROUND + 1);
+     wc.lpszMenuName  = NULL;
+     wc.lpszClassName = g_WndClassName;
+
+     ATOM atomWindowClass = RegisterClass(&wc);
+
+     if (atomWindowClass != 0)
+     {
+         /* Create the window. */
+         hwnd = CreateWindowEx(WS_EX_TOOLWINDOW | WS_EX_TRANSPARENT | WS_EX_TOPMOST,
+                               g_WndClassName, g_WndClassName, WS_POPUPWINDOW,
+                               -200, -200, 100, 100, NULL, NULL, hInstance, NULL);
+
+         if (hwnd)
+         {
+             SetWindowPos(hwnd, HWND_TOPMOST, -200, -200, 0, 0,
+                          SWP_NOACTIVATE | SWP_HIDEWINDOW | SWP_NOCOPYBITS | SWP_NOREDRAW | SWP_NOSIZE);
+
+             MSG msg;
+             while (GetMessage(&msg, NULL, 0, 0))
+             {
+                 TranslateMessage(&msg);
+                 DispatchMessage(&msg);
+             }
+
+             DestroyWindow (hwnd);
+
+             bExit = true;
+         }
+
+         UnregisterClass (g_WndClassName, hInstance);
+     }
+
+     if(bExit)
+     {
+         /* no need any accuracy here, in anyway the DHCP server usually gets terminated with TerminateProcess */
+         exit(0);
+     }
+
+     return 0;
+}
+#  endif
+
+
+/** (We don't want a console usually.) */
+int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
+{
+    RT_NOREF(hInstance, hPrevInstance, lpCmdLine, nCmdShow);
+#  if 0 /* some copy and paste from DHCP that nobody explained why was diabled. */
+    NOREF(hInstance); NOREF(hPrevInstance); NOREF(lpCmdLine); NOREF(nCmdShow);
+
+    HANDLE hThread = CreateThread(
+      NULL, /*__in_opt   LPSECURITY_ATTRIBUTES lpThreadAttributes, */
+      0, /*__in       SIZE_T dwStackSize, */
+      MsgThreadProc, /*__in       LPTHREAD_START_ROUTINE lpStartAddress,*/
+      NULL, /*__in_opt   LPVOID lpParameter,*/
+      0, /*__in       DWORD dwCreationFlags,*/
+      NULL /*__out_opt  LPDWORD lpThreadId*/
+    );
+
+    if(hThread != NULL)
+        CloseHandle(hThread);
+
+#  endif
+    return main(__argc, __argv, environ);
+}
+# endif /* RT_OS_WINDOWS */
+
+#endif /* !VBOX_WITH_HARDENING */
diff --git a/src/VBox/NetworkServices/NAT/VBoxNetNATHardened.cpp b/src/VBox/NetworkServices/NAT/VBoxNetNATHardened.cpp
new file mode 100644
index 00000000..34a0992b
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/VBoxNetNATHardened.cpp
@@ -0,0 +1,37 @@
+/* $Id: VBoxNetNATHardened.cpp $ */
+/** @file
+ * VBoxNetNAT - Hardened main().
+ */
+
+/*
+ * Copyright (C) 2009-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#include <VBox/sup.h>
+
+#ifndef SERVICE_NAME
+# error "Please define SERVICE_NAME"
+#endif
+
+int main(int argc, char **argv, char **envp)
+{
+    return SUPR3HardenedMain(SERVICE_NAME, 0 /* fFlags */, argc, argv, envp);
+}
diff --git a/src/VBox/NetworkServices/NAT/dhcp6.h b/src/VBox/NetworkServices/NAT/dhcp6.h
new file mode 100644
index 00000000..03b26eae
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/dhcp6.h
@@ -0,0 +1,61 @@
+/* $Id: dhcp6.h $ */
+/** @file
+ * NAT Network - DHCPv6 protocol definitions.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#ifndef VBOX_INCLUDED_SRC_NAT_dhcp6_h
+#define VBOX_INCLUDED_SRC_NAT_dhcp6_h
+#ifndef RT_WITHOUT_PRAGMA_ONCE
+# pragma once
+#endif
+
+/* UDP ports */
+#define DHCP6_CLIENT_PORT       546
+#define DHCP6_SERVER_PORT       547
+
+/* Message types */
+#define DHCP6_REPLY                     7
+#define DHCP6_INFORMATION_REQUEST       11
+#define DHCP6_RELAY_FORW                12
+#define DHCP6_RELAY_REPLY               13
+
+/* DUID types */
+#define DHCP6_DUID_LLT                  1
+#define DHCP6_DUID_EN                   2
+#define DHCP6_DUID_LL                   3
+
+/* Hardware type for DUID-LLT and DUID-LL */
+#define ARES_HRD_ETHERNET               1 /* RFC 826*/
+
+/* Options */
+#define DHCP6_OPTION_CLIENTID           1
+#define DHCP6_OPTION_SERVERID           2
+#define DHCP6_OPTION_ORO                6
+#define DHCP6_OPTION_ELAPSED_TIME       8
+#define DHCP6_OPTION_STATUS_CODE        13
+#define DHCP6_OPTION_DNS_SERVERS        23 /* RFC 3646 */
+#define DHCP6_OPTION_DOMAIN_LIST        24 /* RFC 3646 */
+
+#endif /* !VBOX_INCLUDED_SRC_NAT_dhcp6_h */
diff --git a/src/VBox/NetworkServices/NAT/fwtcp.c b/src/VBox/NetworkServices/NAT/fwtcp.c
new file mode 100644
index 00000000..79cdfc04
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/fwtcp.c
@@ -0,0 +1,333 @@
+/* $Id: fwtcp.c $ */
+/** @file
+ * NAT Network - TCP port-forwarding.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#define LOG_GROUP LOG_GROUP_NAT_SERVICE
+
+#include "winutils.h"
+#include "proxy.h"
+#include "proxy_pollmgr.h"
+#include "portfwd.h"
+#include "pxtcp.h"
+
+#ifndef RT_OS_WINDOWS
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <arpa/inet.h>
+#include <stdio.h>
+#include <poll.h>
+
+#include <err.h>                /* BSD'ism */
+#else
+#include <stdio.h>
+#include "winpoll.h"
+#endif
+
+#include "lwip/opt.h"
+
+#include "lwip/sys.h"
+#include "lwip/tcpip.h"
+
+
+/**
+ */
+struct fwtcp {
+    /**
+     * Our poll manager handler.
+     */
+    struct pollmgr_handler pmhdl;
+
+    /**
+     * Forwarding specification.
+     */
+    struct fwspec fwspec;
+
+    /**
+     * Listening socket.
+     */
+    SOCKET sock;
+
+    /**
+     * Mailbox for new inbound connections.
+     *
+     * XXX: since we have single producer and single consumer we can
+     * use lockless ringbuf like for pxtcp.
+     */
+    sys_mbox_t connmbox;
+
+    struct tcpip_msg msg_connect;
+    struct tcpip_msg msg_delete;
+
+    /**
+     * Linked list entry.
+     */
+    struct fwtcp *next;
+};
+
+
+static struct fwtcp *fwtcp_create(struct fwspec *);
+
+/* poll manager callback for fwtcp listening socket */
+static int fwtcp_pmgr_listen(struct pollmgr_handler *, SOCKET, int);
+
+/* lwip thread callbacks called via proxy_lwip_post() */
+static void fwtcp_pcb_connect(void *);
+static void fwtcp_pcb_delete(void *);
+
+
+/**
+ * Linked list of active fwtcp forwarders.
+ */
+struct fwtcp *fwtcp_list = NULL;
+
+
+void
+fwtcp_init(void)
+{
+    return;
+}
+
+
+void
+fwtcp_add(struct fwspec *fwspec)
+{
+    struct fwtcp *fwtcp;
+
+    fwtcp = fwtcp_create(fwspec);
+    if (fwtcp == NULL) {
+        DPRINTF0(("%s: failed to add rule for TCP ...\n", __func__));
+        return;
+    }
+
+    DPRINTF0(("%s\n", __func__));
+    /* fwtcp_create has put fwtcp on the linked list */
+}
+
+
+void
+fwtcp_del(struct fwspec *fwspec)
+{
+    struct fwtcp *fwtcp;
+    struct fwtcp **pprev;
+
+    for (pprev = &fwtcp_list; (fwtcp = *pprev) != NULL; pprev = &fwtcp->next) {
+        if (fwspec_equal(&fwtcp->fwspec, fwspec)) {
+            *pprev = fwtcp->next;
+            fwtcp->next = NULL;
+            break;
+        }
+    }
+
+    if (fwtcp == NULL) {
+        DPRINTF0(("%s: not found\n", __func__));
+        return;
+    }
+
+    DPRINTF0(("%s\n", __func__));
+
+    pollmgr_del_slot(fwtcp->pmhdl.slot);
+    fwtcp->pmhdl.slot = -1;
+
+    closesocket(fwtcp->sock);
+    fwtcp->sock = INVALID_SOCKET;
+
+    /* let pending msg_connect be processed before we delete fwtcp */
+    proxy_lwip_post(&fwtcp->msg_delete);
+}
+
+
+struct fwtcp *
+fwtcp_create(struct fwspec *fwspec)
+{
+    struct fwtcp *fwtcp;
+    SOCKET lsock;
+    int status;
+    err_t error;
+
+    lsock = proxy_bound_socket(fwspec->sdom, fwspec->stype, &fwspec->src.sa);
+    if (lsock == INVALID_SOCKET) {
+        return NULL;
+    }
+
+    fwtcp = (struct fwtcp *)malloc(sizeof(*fwtcp));
+    if (fwtcp == NULL) {
+        closesocket(lsock);
+        return NULL;
+    }
+
+    fwtcp->pmhdl.callback = fwtcp_pmgr_listen;
+    fwtcp->pmhdl.data = (void *)fwtcp;
+    fwtcp->pmhdl.slot = -1;
+
+    fwtcp->sock = lsock;
+    fwtcp->fwspec = *fwspec;    /* struct copy */
+
+    error = sys_mbox_new(&fwtcp->connmbox, 16);
+    if (error != ERR_OK) {
+        closesocket(lsock);
+        free(fwtcp);
+        return (NULL);
+    }
+
+#define CALLBACK_MSG(MSG, FUNC)                         \
+    do {                                                \
+        fwtcp->MSG.type = TCPIP_MSG_CALLBACK_STATIC;    \
+        fwtcp->MSG.sem = NULL;                          \
+        fwtcp->MSG.msg.cb.function = FUNC;              \
+        fwtcp->MSG.msg.cb.ctx = (void *)fwtcp;          \
+    } while (0)
+
+    CALLBACK_MSG(msg_connect, fwtcp_pcb_connect);
+    CALLBACK_MSG(msg_delete,  fwtcp_pcb_delete);
+
+#undef CALLBACK_MSG
+
+    status = pollmgr_add(&fwtcp->pmhdl, fwtcp->sock, POLLIN);
+    if (status < 0) {
+        sys_mbox_free(&fwtcp->connmbox);
+        closesocket(lsock);
+        free(fwtcp);
+        return NULL;
+    }
+
+    fwtcp->next = fwtcp_list;
+    fwtcp_list = fwtcp;
+
+    return fwtcp;
+}
+
+
+int
+fwtcp_pmgr_listen(struct pollmgr_handler *handler, SOCKET fd, int revents)
+{
+    struct fwtcp *fwtcp;
+    struct sockaddr_storage ss;
+    socklen_t sslen;
+    struct pxtcp *pxtcp;
+    SOCKET newsock;
+    int status;
+    err_t error;
+
+    fwtcp = (struct fwtcp *)handler->data;
+    pxtcp = NULL;
+
+    LWIP_ASSERT1(fwtcp != NULL);
+    LWIP_ASSERT1(fd == fwtcp->sock);
+    LWIP_ASSERT1(revents == POLLIN);
+    LWIP_UNUSED_ARG(fd);
+    LWIP_UNUSED_ARG(revents);
+
+    LWIP_ASSERT1(sys_mbox_valid(&fwtcp->connmbox));
+
+    sslen = sizeof(ss);
+    newsock = accept(fwtcp->sock, (struct sockaddr *)&ss, &sslen);
+    if (newsock == INVALID_SOCKET) {
+        return POLLIN;
+    }
+
+#ifdef RT_OS_LINUX
+    status = proxy_fixup_accepted_socket(newsock);
+    if (status < 0) {
+        proxy_reset_socket(newsock);
+        return POLLIN;
+    }
+#endif
+
+    if (ss.ss_family == PF_INET) {
+        struct sockaddr_in *peer4 = (struct sockaddr_in *)&ss;
+        RT_NOREF(peer4);
+        DPRINTF(("<--- TCP %RTnaipv4:%d\n",
+                 peer4->sin_addr.s_addr, ntohs(peer4->sin_port)));
+    }
+    else { /* PF_INET6 */
+        struct sockaddr_in6 *peer6 = (struct sockaddr_in6 *)&ss;
+        RT_NOREF(peer6);
+        DPRINTF(("<--- TCP %RTnaipv6:%d\n",
+                 &peer6->sin6_addr, ntohs(peer6->sin6_port)));
+    }
+
+    pxtcp = pxtcp_create_forwarded(newsock);
+    if (pxtcp == NULL) {
+        proxy_reset_socket(newsock);
+        return POLLIN;
+    }
+
+    status = pxtcp_pmgr_add(pxtcp);
+    if (status < 0) {
+        pxtcp_cancel_forwarded(pxtcp);
+        return POLLIN;
+    }
+
+    error = sys_mbox_trypost(&fwtcp->connmbox, (void *)pxtcp);
+    if (error != ERR_OK) {
+        pxtcp_pmgr_del(pxtcp);
+        pxtcp_cancel_forwarded(pxtcp);
+        return POLLIN;
+    }
+
+    proxy_lwip_post(&fwtcp->msg_connect);
+    return POLLIN;
+}
+
+
+void
+fwtcp_pcb_connect(void *arg)
+{
+    struct fwtcp *fwtcp = (struct fwtcp *)arg;
+    struct pxtcp *pxtcp;
+    u32_t timo;
+
+    if (!sys_mbox_valid(&fwtcp->connmbox)) {
+        return;
+    }
+
+    pxtcp = NULL;
+    timo = sys_mbox_tryfetch(&fwtcp->connmbox, (void **)&pxtcp);
+    if (timo == SYS_MBOX_EMPTY) {
+        return;
+    }
+
+    LWIP_ASSERT1(pxtcp != NULL);
+
+    /* hand off to pxtcp */
+    pxtcp_pcb_connect(pxtcp, &fwtcp->fwspec);
+}
+
+
+static void
+fwtcp_pcb_delete(void *arg)
+{
+    struct fwtcp *fwtcp = (struct fwtcp *)arg;
+    void *data;
+    u32_t timo;
+
+    timo = sys_mbox_tryfetch(&fwtcp->connmbox, &data);
+    LWIP_ASSERT1(timo == SYS_MBOX_EMPTY);
+    LWIP_UNUSED_ARG(timo);      /* only in assert */
+
+    sys_mbox_free(&fwtcp->connmbox);
+    free(fwtcp);
+}
diff --git a/src/VBox/NetworkServices/NAT/fwudp.c b/src/VBox/NetworkServices/NAT/fwudp.c
new file mode 100644
index 00000000..7c0b69f9
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/fwudp.c
@@ -0,0 +1,555 @@
+/* $Id: fwudp.c $ */
+/** @file
+ * NAT Network - UDP port-forwarding.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#define LOG_GROUP LOG_GROUP_NAT_SERVICE
+
+#include "winutils.h"
+#include "proxy.h"
+#include "proxy_pollmgr.h"
+#include "portfwd.h"
+#include "pxremap.h"
+
+#ifndef RT_OS_WINDOWS
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <stdio.h>
+#include <string.h>
+#include <poll.h>
+
+#include <err.h>                /* BSD'ism */
+#else
+#include <stdio.h>
+#include <string.h>
+#include "winpoll.h"
+#endif
+
+#include "lwip/opt.h"
+#include "lwip/memp.h"          /* XXX: for bulk delete of pcbs */
+
+#include "lwip/sys.h"
+#include "lwip/tcpip.h"
+#include "lwip/udp.h"
+
+struct fwudp_dgram {
+    struct pbuf *p;
+    ipX_addr_t src_addr;
+    u16_t src_port;
+};
+
+/**
+ * UDP port-forwarding.
+ *
+ * Unlike pxudp that uses 1:1 mapping between pcb and socket, for
+ * port-forwarded UDP the setup is bit more elaborated.
+ *
+ * For fwtcp things are simple since incoming TCP connection get a new
+ * socket that we just hand off to pxtcp. Thus fwtcp only handles
+ * connection initiation.
+ *
+ * For fwudp all proxied UDP conversations share the same socket, so
+ * single fwudp multiplexes to several UDP pcbs.
+ *
+ * XXX: TODO: Currently pcbs point back directly to fwudp.  It might
+ * make sense to introduce a per-pcb structure that points to fwudp
+ * and carries additional information, like pre-mapped peer address.
+ */
+struct fwudp {
+    /**
+     * Our poll manager handler.
+     */
+    struct pollmgr_handler pmhdl;
+
+    /**
+     * Forwarding specification.
+     */
+    struct fwspec fwspec;
+
+    /**
+     * XXX: lwip-format copy of destination
+     */
+    ipX_addr_t dst_addr;
+    u16_t dst_port;
+
+    /**
+     * Listening socket.
+     */
+    SOCKET sock;
+
+    /**
+     * Ring-buffer for inbound datagrams.
+     */
+    struct {
+        struct fwudp_dgram *buf;
+        size_t bufsize;
+        volatile size_t vacant;
+        volatile size_t unsent;
+    } inbuf;
+
+    struct tcpip_msg msg_send;
+    struct tcpip_msg msg_delete;
+
+    struct fwudp *next;
+};
+
+
+struct fwudp *fwudp_create(struct fwspec *);
+
+/* poll manager callback for fwudp socket */
+static int fwudp_pmgr_pump(struct pollmgr_handler *, SOCKET, int);
+
+/* lwip thread callbacks called via proxy_lwip_post() */
+static void fwudp_pcb_send(void *);
+static void fwudp_pcb_delete(void *);
+
+static void fwudp_pcb_recv(void *, struct udp_pcb *, struct pbuf *, ip_addr_t *, u16_t);
+static void fwudp_pcb_forward_outbound(struct fwudp *, struct udp_pcb *, struct pbuf *);
+
+
+/**
+ * Linked list of active fwtcp forwarders.
+ */
+struct fwudp *fwudp_list = NULL;
+
+
+void
+fwudp_init(void)
+{
+    return;
+}
+
+
+void
+fwudp_add(struct fwspec *fwspec)
+{
+    struct fwudp *fwudp;
+
+    fwudp = fwudp_create(fwspec);
+    if (fwudp == NULL) {
+        DPRINTF0(("%s: failed to add rule for UDP ...\n", __func__));
+        return;
+    }
+
+    DPRINTF0(("%s\n", __func__));
+    /* fwudp_create has put fwudp on the linked list */
+}
+
+
+void
+fwudp_del(struct fwspec *fwspec)
+{
+    struct fwudp *fwudp;
+    struct fwudp **pprev;
+
+    for (pprev = &fwudp_list; (fwudp = *pprev) != NULL; pprev = &fwudp->next) {
+        if (fwspec_equal(&fwudp->fwspec, fwspec)) {
+            *pprev = fwudp->next;
+            fwudp->next = NULL;
+            break;
+        }
+    }
+
+    if (fwudp == NULL) {
+        DPRINTF0(("%s: not found\n", __func__));
+        return;
+    }
+
+    DPRINTF0(("%s\n", __func__));
+
+    pollmgr_del_slot(fwudp->pmhdl.slot);
+    fwudp->pmhdl.slot = -1;
+
+    /* let pending msg_send be processed before we delete fwudp */
+    proxy_lwip_post(&fwudp->msg_delete);
+}
+
+
+struct fwudp *
+fwudp_create(struct fwspec *fwspec)
+{
+    struct fwudp *fwudp;
+    SOCKET sock;
+    int status;
+
+    sock = proxy_bound_socket(fwspec->sdom, fwspec->stype, &fwspec->src.sa);
+    if (sock == INVALID_SOCKET) {
+        return NULL;
+    }
+
+    fwudp = (struct fwudp *)malloc(sizeof(*fwudp));
+    if (fwudp == NULL) {
+        closesocket(sock);
+        return NULL;
+    }
+
+    fwudp->pmhdl.callback = fwudp_pmgr_pump;
+    fwudp->pmhdl.data = (void *)fwudp;
+    fwudp->pmhdl.slot = -1;
+
+    fwudp->sock = sock;
+    fwudp->fwspec = *fwspec;    /* struct copy */
+
+    /* XXX */
+    if (fwspec->sdom == PF_INET) {
+        struct sockaddr_in *dst4 = &fwspec->dst.sin;
+        memcpy(&fwudp->dst_addr.ip4, &dst4->sin_addr, sizeof(ip_addr_t));
+        fwudp->dst_port = htons(dst4->sin_port);
+    }
+    else { /* PF_INET6 */
+        struct sockaddr_in6 *dst6 = &fwspec->dst.sin6;
+        memcpy(&fwudp->dst_addr.ip6, &dst6->sin6_addr, sizeof(ip6_addr_t));
+        fwudp->dst_port = htons(dst6->sin6_port);
+    }
+
+    fwudp->inbuf.bufsize = 256; /* elements  */
+    fwudp->inbuf.buf
+        = (struct fwudp_dgram *)calloc(fwudp->inbuf.bufsize,
+                                       sizeof(struct fwudp_dgram));
+    if (fwudp->inbuf.buf == NULL) {
+        closesocket(sock);
+        free(fwudp);
+        return (NULL);
+    }
+    fwudp->inbuf.vacant = 0;
+    fwudp->inbuf.unsent = 0;
+
+#define CALLBACK_MSG(MSG, FUNC)                         \
+    do {                                                \
+        fwudp->MSG.type = TCPIP_MSG_CALLBACK_STATIC;    \
+        fwudp->MSG.sem = NULL;                          \
+        fwudp->MSG.msg.cb.function = FUNC;              \
+        fwudp->MSG.msg.cb.ctx = (void *)fwudp;          \
+    } while (0)
+
+    CALLBACK_MSG(msg_send, fwudp_pcb_send);
+    CALLBACK_MSG(msg_delete, fwudp_pcb_delete);
+
+#undef CALLBACK_MSG
+
+    status = pollmgr_add(&fwudp->pmhdl, fwudp->sock, POLLIN);
+    if (status < 0) {
+        closesocket(sock);
+        free(fwudp->inbuf.buf);
+        free(fwudp);
+        return NULL;
+    }
+
+    fwudp->next = fwudp_list;
+    fwudp_list = fwudp;
+
+    return fwudp;
+}
+
+
+/**
+ * Poll manager callaback for fwudp::sock
+ */
+int
+fwudp_pmgr_pump(struct pollmgr_handler *handler, SOCKET fd, int revents)
+{
+    struct fwudp *fwudp;
+    struct sockaddr_storage ss;
+    socklen_t sslen = sizeof(ss);
+    size_t beg, lim;
+    struct fwudp_dgram *dgram;
+    struct pbuf *p;
+    ssize_t nread;
+    int status;
+    err_t error;
+
+    fwudp = (struct fwudp *)handler->data;
+
+    LWIP_ASSERT1(fwudp != NULL);
+    LWIP_ASSERT1(fd == fwudp->sock);
+    LWIP_ASSERT1(revents == POLLIN);
+    LWIP_UNUSED_ARG(fd);
+    LWIP_UNUSED_ARG(revents);
+
+#ifdef RT_OS_WINDOWS
+    nread = recvfrom(fwudp->sock, (char *)pollmgr_udpbuf, sizeof(pollmgr_udpbuf), 0,
+                     (struct sockaddr *)&ss, &sslen);
+#else
+    nread = recvfrom(fwudp->sock, pollmgr_udpbuf, sizeof(pollmgr_udpbuf), 0,
+                     (struct sockaddr *)&ss, &sslen);
+#endif
+    if (nread < 0) {
+        DPRINTF(("%s: %R[sockerr]\n", __func__, SOCKERRNO()));
+        return POLLIN;
+    }
+
+    /* Check that ring buffer is not full */
+    lim = fwudp->inbuf.unsent;
+    if (lim == 0) {
+        lim = fwudp->inbuf.bufsize - 1; /* guard slot at the end */
+    }
+    else {
+        --lim;
+    }
+
+    beg = fwudp->inbuf.vacant;
+    if (beg == lim) { /* no vacant slot */
+        return POLLIN;
+    }
+
+
+    dgram = &fwudp->inbuf.buf[beg];
+
+
+    status = fwany_ipX_addr_set_src(&dgram->src_addr, (struct sockaddr *)&ss);
+    if (status == PXREMAP_FAILED) {
+        return POLLIN;
+    }
+
+    if (ss.ss_family == AF_INET) {
+        const struct sockaddr_in *peer4 = (const struct sockaddr_in *)&ss;
+        dgram->src_port = htons(peer4->sin_port);
+    }
+    else { /* PF_INET6 */
+        const struct sockaddr_in6 *peer6 = (const struct sockaddr_in6 *)&ss;
+        dgram->src_port = htons(peer6->sin6_port);
+    }
+
+    p = pbuf_alloc(PBUF_RAW, nread, PBUF_RAM);
+    if (p == NULL) {
+        DPRINTF(("%s: pbuf_alloc(%d) failed\n", __func__, (int)nread));
+        return POLLIN;
+    }
+
+    error = pbuf_take(p, pollmgr_udpbuf, nread);
+    if (error != ERR_OK) {
+        DPRINTF(("%s: pbuf_take(%d) failed\n", __func__, (int)nread));
+        pbuf_free(p);
+        return POLLIN;
+    }
+
+    dgram->p = p;
+
+    ++beg;
+    if (beg == fwudp->inbuf.bufsize) {
+        beg = 0;
+    }
+    fwudp->inbuf.vacant = beg;
+
+    proxy_lwip_post(&fwudp->msg_send);
+
+    return POLLIN;
+}
+
+
+/**
+ * Lwip thread callback invoked via fwudp::msg_send
+ */
+void
+fwudp_pcb_send(void *arg)
+{
+    struct fwudp *fwudp = (struct fwudp *)arg;
+    struct fwudp_dgram dgram;
+    struct udp_pcb *pcb;
+    struct udp_pcb **pprev;
+    int isv6;
+    size_t idx;
+
+    idx = fwudp->inbuf.unsent;
+
+    if (idx == fwudp->inbuf.vacant) {
+        /* empty buffer - shouldn't happen! */
+        DPRINTF(("%s: ring buffer empty!\n", __func__));
+        return;
+    }
+
+    dgram = fwudp->inbuf.buf[idx]; /* struct copy */
+#if 1 /* valgrind hint */
+    fwudp->inbuf.buf[idx].p = NULL;
+#endif
+    if (++idx == fwudp->inbuf.bufsize) {
+        idx = 0;
+    }
+    fwudp->inbuf.unsent = idx;
+
+    /* XXX: this is *STUPID* */
+    isv6 = (fwudp->fwspec.sdom == PF_INET6);
+    pprev = &udp_proxy_pcbs;
+    for (pcb = udp_proxy_pcbs; pcb != NULL; pcb = pcb->next) {
+        if (PCB_ISIPV6(pcb) == isv6
+            && pcb->remote_port == fwudp->dst_port
+            && ipX_addr_cmp(isv6, &fwudp->dst_addr, &pcb->remote_ip)
+            && pcb->local_port == dgram.src_port
+            && ipX_addr_cmp(isv6, &dgram.src_addr, &pcb->local_ip))
+        {
+            break;
+        }
+        else {
+            pprev = &pcb->next;
+        }
+    }
+
+    if (pcb != NULL) {
+        *pprev = pcb->next;
+        pcb->next = udp_proxy_pcbs;
+        udp_proxy_pcbs = pcb;
+
+        /*
+         * XXX: check that its ours and not accidentally created by
+         * outbound traffic.
+         *
+         * ???: Otherwise?  Expire it and set pcb = NULL; to create a
+         * new one below?
+         */
+    }
+
+    if (pcb == NULL) {
+        pcb = udp_new();
+        if (pcb == NULL) {
+            goto out;
+        }
+
+        ip_set_v6(pcb, isv6);
+
+        /* equivalent of udp_bind */
+        ipX_addr_set(isv6, &pcb->local_ip, &dgram.src_addr);
+        pcb->local_port = dgram.src_port;
+
+        /* equivalent to udp_connect */
+        ipX_addr_set(isv6, &pcb->remote_ip, &fwudp->dst_addr);
+        pcb->remote_port = fwudp->dst_port;
+        pcb->flags |= UDP_FLAGS_CONNECTED;
+
+        udp_recv(pcb, fwudp_pcb_recv, fwudp);
+
+        pcb->next = udp_proxy_pcbs;
+        udp_proxy_pcbs = pcb;
+        udp_proxy_timer_needed();
+    }
+
+    udp_send(pcb, dgram.p);
+
+  out:
+    pbuf_free(dgram.p);
+}
+
+
+/**
+ * udp_recv() callback.
+ */
+void
+fwudp_pcb_recv(void *arg, struct udp_pcb *pcb, struct pbuf *p,
+               ip_addr_t *addr, u16_t port)
+{
+    struct fwudp *fwudp = (struct fwudp *)arg;
+
+    LWIP_UNUSED_ARG(addr);
+    LWIP_UNUSED_ARG(port);
+
+    LWIP_ASSERT1(fwudp != NULL);
+
+    if (p == NULL) {
+        DPRINTF(("%s: pcb %p (fwudp %p); sock %d: expired\n",
+                 __func__, (void *)pcb, (void *)fwudp, fwudp->sock));
+        /* NB: fwudp is "global" and not deleted */
+        /* XXX: TODO: delete local reference when we will keep one */
+        udp_remove(pcb);
+        return;
+    }
+    else {
+        fwudp_pcb_forward_outbound(fwudp, pcb, p);
+    }
+}
+
+
+/*
+ * XXX: This is pxudp_pcb_forward_outbound modulo:
+ * - s/pxudp/fwudp/g
+ * - addr/port (unused in either) dropped
+ * - destination is specified since host socket is not connected
+ */
+static void
+fwudp_pcb_forward_outbound(struct fwudp *fwudp, struct udp_pcb *pcb,
+                           struct pbuf *p)
+{
+    union {
+        struct sockaddr_in sin;
+        struct sockaddr_in6 sin6;
+    } peer;
+    socklen_t namelen;
+
+    memset(&peer, 0, sizeof(peer)); /* XXX: shut up valgrind */
+
+    if (fwudp->fwspec.sdom == PF_INET) {
+        peer.sin.sin_family = AF_INET;
+#if HAVE_SA_LEN
+        peer.sin.sin_len =
+#endif
+        namelen = sizeof(peer.sin);
+        pxremap_outbound_ip4((ip_addr_t *)&peer.sin.sin_addr, &pcb->local_ip.ip4);
+        peer.sin.sin_port = htons(pcb->local_port);
+    }
+    else {
+        peer.sin6.sin6_family = AF_INET6;
+#if HAVE_SA_LEN
+        peer.sin6.sin6_len =
+#endif
+        namelen = sizeof(peer.sin6);
+
+        pxremap_outbound_ip6((ip6_addr_t *)&peer.sin6.sin6_addr, &pcb->local_ip.ip6);
+        peer.sin6.sin6_port = htons(pcb->local_port);
+    }
+
+    proxy_sendto(fwudp->sock, p, &peer, namelen);
+    pbuf_free(p);
+}
+
+
+/**
+ * Lwip thread callback invoked via fwudp::msg_delete
+ */
+static void
+fwudp_pcb_delete(void *arg)
+{
+    struct fwudp *fwudp = (struct fwudp *)arg;
+    struct udp_pcb *pcb;
+    struct udp_pcb **pprev;
+
+    LWIP_ASSERT1(fwudp->inbuf.unsent == fwudp->inbuf.vacant);
+
+    pprev = &udp_proxy_pcbs;
+    pcb = udp_proxy_pcbs;
+    while (pcb != NULL) {
+        if (pcb->recv_arg != fwudp) {
+            pprev = &pcb->next;
+            pcb = pcb->next;
+        }
+        else {
+            struct udp_pcb *dead = pcb;
+            pcb = pcb->next;
+            *pprev = pcb;
+            memp_free(MEMP_UDP_PCB, dead);
+        }
+    }
+
+    closesocket(fwudp->sock);
+    free(fwudp->inbuf.buf);
+    free(fwudp);
+}
diff --git a/src/VBox/NetworkServices/NAT/getrawsock.c b/src/VBox/NetworkServices/NAT/getrawsock.c
new file mode 100644
index 00000000..8b93ff6f
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/getrawsock.c
@@ -0,0 +1,165 @@
+/* $Id: getrawsock.c $ */
+/** @file
+ * Obtain raw-sockets from a server when debugging unprivileged.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <netinet/in.h>
+#include <errno.h>
+#include <pwd.h>
+#include <signal.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+/* XXX: this should be in a header, but isn't.  naughty me. :( */
+int getrawsock(int type);
+
+
+int
+getrawsock(int type)
+{
+    struct sockaddr_un sux;     /* because solaris */
+    struct passwd *pw;
+    size_t pathlen;
+    int rawsock, server;
+    struct msghdr mh;
+    struct iovec iov[1];
+    char buf[1];
+    struct cmsghdr *cmh;
+    char cmsg[CMSG_SPACE(sizeof(int))];
+    ssize_t nread, nsent;
+    int status;
+
+    server = -1;
+    rawsock = -1;
+
+    memset(&sux, 0, sizeof(sux));
+    sux.sun_family = AF_UNIX;
+
+    if (geteuid() == 0) {
+        return -1;
+    }
+
+    if (type == AF_INET) {
+        buf[0] = '4';
+    }
+    else if (type == AF_INET6) {
+        buf[0] = '6';
+    }
+    else {
+        return -1;
+    }
+
+    errno = 0;
+    pw = getpwuid(getuid());
+    if (pw == NULL) {
+        perror("getpwuid");
+        return -1;
+    }
+
+    pathlen = snprintf(sux.sun_path, sizeof(sux.sun_path),
+                       "/tmp/.vbox-%s-aux/mkrawsock", pw->pw_name);
+    if (pathlen > sizeof(sux.sun_path)) {
+        fprintf(stderr, "socket pathname truncated\n");
+        return -1;
+    }
+
+    server = socket(PF_UNIX, SOCK_STREAM, 0);
+    if (server < 0) {
+        perror("socket");
+        return -1;
+    }
+
+    status = connect(server, (struct sockaddr *)&sux,
+                     (sizeof(sux) - sizeof(sux.sun_path)
+                      + strlen(sux.sun_path) + 1));
+    if (status < 0) {
+        perror(sux.sun_path);
+        goto out;
+    }
+
+    nsent = send(server, buf, 1, 0);
+    if (nsent != 1) {
+        if (nsent < 0) {
+            perror("send");
+        }
+        else {
+            fprintf(stderr, "failed to contact mkrawsock\n");
+        }
+        goto out;
+    }
+
+    buf[0] = '\0';
+
+    iov[0].iov_base = buf;
+    iov[0].iov_len = 1;
+
+    memset(&mh, 0, sizeof(mh));
+    mh.msg_iov = iov;
+    mh.msg_iovlen = 1;
+    mh.msg_control = cmsg;
+    mh.msg_controllen = sizeof(cmsg);
+
+    nread = recvmsg(server, &mh, 0);
+    if (nread != 1) {
+        if (nread < 0) {
+            perror("recvmsg");
+        }
+        else {
+            fprintf(stderr, "EOF from mkrawsock\n");
+        }
+        goto out;
+    }
+
+    if ((type == AF_INET && buf[0] != '4')
+        || (type == AF_INET6 && buf[0] != '6')
+        || mh.msg_controllen == 0)
+    {
+        goto out;
+    }
+
+    for (cmh = CMSG_FIRSTHDR(&mh); cmh != NULL; cmh = CMSG_NXTHDR(&mh, cmh)) {
+        if ((cmh->cmsg_level == SOL_SOCKET)
+            && (cmh->cmsg_type == SCM_RIGHTS)
+            && (cmh->cmsg_len == CMSG_LEN(sizeof(rawsock))))
+        {
+            rawsock = *((int *)CMSG_DATA(cmh));
+            break;
+        }
+    }
+
+  out:
+    if (server != -1) {
+        close(server);
+    }
+    if (rawsock != -1) {
+        printf("%s: got ICMPv%c socket %d\n",
+               __func__, type == AF_INET ? '4' : '6', rawsock);
+    }
+    return rawsock;
+}
diff --git a/src/VBox/NetworkServices/NAT/lwipopts.h b/src/VBox/NetworkServices/NAT/lwipopts.h
new file mode 100644
index 00000000..e36b36e0
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/lwipopts.h
@@ -0,0 +1,215 @@
+/* $Id: lwipopts.h $ */
+/** @file
+ * NAT Network - lwIP configuration options.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#ifndef VBOX_INCLUDED_SRC_NAT_lwipopts_h
+#define VBOX_INCLUDED_SRC_NAT_lwipopts_h
+#ifndef RT_WITHOUT_PRAGMA_ONCE
+# pragma once
+#endif
+
+#include <VBox/cdefs.h>     /* For VBOX_STRICT. */
+#include <iprt/mem.h>
+#include <iprt/alloca.h>    /* This may include malloc.h (msc), which is something that has
+                             * to be done before redefining any of the functions therein. */
+#include <iprt/rand.h> /* see LWIP_RAND() definition */
+
+/* lwip/sockets.h assumes that if FD_SET is defined (in case of Innotek GCC
+ * its definition is dragged through iprt/types.h) then struct timeval is
+ * defined as well, but it's not the case. So include it manually. */
+#ifdef RT_OS_OS2
+# include <sys/time.h>
+#endif
+
+/** Make lwIP use the libc malloc, or more precisely (see below) the IPRT
+ * memory allocation functions. */
+#define MEM_LIBC_MALLOC 1
+
+/** Set proper memory alignment. */
+#if HC_ARCH_BITS == 64
+# define MEM_ALIGNMENT 8
+#else
+#define MEM_ALIGNMENT 4
+#endif
+
+/* Padding before Ethernet header to make IP header aligned */
+#define ETH_PAD_SIZE 2
+
+/* IP */
+#define IP_REASSEMBLY 1
+#define IP_REASS_MAX_PBUFS      128
+
+
+
+/** Increase maximum TCP window size. */
+#define TCP_WND 32768
+
+/** Increase TCP maximum segment size. */
+#define TCP_MSS 1460
+
+/** Enable queueing of out-of-order segments. */
+#define TCP_QUEUE_OOSEQ 1
+
+/** TCP sender buffer space (bytes). */
+#define TCP_SND_BUF (32 * TCP_MSS)
+
+/* TCP sender buffer space (pbufs). This must be at least = 2 *
+   TCP_SND_BUF/TCP_MSS for things to work. */
+#define TCP_SND_QUEUELEN        128
+
+/* MEMP_NUM_PBUF: the number of memp struct pbufs. If the application
+   sends a lot of data out of ROM (or other static memory), this
+   should be set high.
+
+   NB: This is for PBUF_ROM and PBUF_REF pbufs only!
+
+   Number of PBUF_POOL pbufs is controlled by PBUF_POOL_SIZE that,
+   somewhat confusingly, breaks MEMP_NUM_* pattern.
+
+   PBUF_RAM pbufs are allocated with mem_malloc (with MEM_LIBC_MALLOC
+   set to 1 this is just system malloc), not memp_malloc.  */
+#define MEMP_NUM_PBUF (1024 * 4)
+
+
+/* MEMP_NUM_MLD6_GROUP: Maximum number of IPv6 multicast groups that
+   can be joined.
+
+   We need to be able to join solicited node multicast for each
+   address (potentially different) and two groups for DHCP6.  All
+   routers multicast is hardcoded in ip6.c and does not require
+   explicit joining.  Provide also for a few extra groups just in
+   case.  */
+#define MEMP_NUM_MLD6_GROUP     (LWIP_IPV6_NUM_ADDRESSES + /* dhcp6 */ 2 + /* extra */ 8)
+
+
+/* MEMP_NUM_TCP_SEG: the number of simultaneously queued TCP
+   segments. */
+#define MEMP_NUM_TCP_SEG (MEMP_NUM_TCP_PCB * TCP_SND_QUEUELEN / 2)
+
+/* MEMP_NUM_TCP_PCB: the number of simulatenously active TCP
+   connections. */
+#define MEMP_NUM_TCP_PCB        128
+
+/* MEMP_NUM_TCPIP_MSG_*: the number of struct tcpip_msg, which is used
+   for sequential API communication and incoming packets. Used in
+   src/api/tcpip.c. */
+#define MEMP_NUM_TCPIP_MSG_API   128
+#define MEMP_NUM_TCPIP_MSG_INPKT 1024
+
+/* MEMP_NUM_UDP_PCB: the number of UDP protocol control blocks. One
+   per active UDP "connection". */
+#define MEMP_NUM_UDP_PCB        32
+
+/* Pbuf options */
+/* PBUF_POOL_SIZE: the number of buffers in the pbuf pool.
+   This is only for PBUF_POOL pbufs, primarily used by netif drivers.
+
+   This should have been named with the MEMP_NUM_ prefix (cf.
+   MEMP_NUM_PBUF for PBUF_ROM and PBUF_REF) as it controls the size of
+   yet another memp_malloc() pool.  */
+#define PBUF_POOL_SIZE          (1024 * 4)
+
+/* PBUF_POOL_BUFSIZE: the size of each pbuf in the pbuf pool.
+   Use default that is based on TCP_MSS and PBUF_LINK_HLEN.  */
+#undef PBUF_POOL_BUFSIZE
+
+/** Turn on support for lightweight critical region protection. Leaving this
+ * off uses synchronization code in pbuf.c which is totally polluted with
+ * races. All the other lwip source files would fall back to semaphore-based
+ * synchronization, but pbuf.c is just broken, leading to incorrect allocation
+ * and as a result to assertions due to buffers being double freed. */
+#define SYS_LIGHTWEIGHT_PROT 1
+
+/** Attempt to get rid of htons etc. macro issues. */
+#undef LWIP_PREFIX_BYTEORDER_FUNCS
+
+#define LWIP_TCPIP_CORE_LOCKING_INPUT 0
+#define LWIP_TCPIP_CORE_LOCKING 0
+#define LWIP_TCP 1
+#define LWIP_SOCKET 0
+#define LWIP_ARP 1
+#define ARP_PROXY 1
+#define LWIP_ETHERNET 1
+#define LWIP_COMPAT_SOCKETS 0
+#define LWIP_COMPAT_MUTEX 1
+
+#define LWIP_IPV6 1
+#define LWIP_IPV6_FORWARD 1
+#define LWIP_ND6_PROXY 1
+
+#define LWIP_ND6_ALLOW_RA_UPDATES       (!LWIP_IPV6_FORWARD)
+#define LWIP_IPV6_SEND_ROUTER_SOLICIT   (!LWIP_IPV6_FORWARD)
+/* IPv6 autoconfig we don't need in proxy, but it required for very seldom cases
+ * iSCSI over intnet with IPv6
+ */
+#define LWIP_IPV6_AUTOCONFIG            1
+#if LWIP_IPV6_FORWARD /* otherwise use the default from lwip/opt.h */
+#define LWIP_IPV6_DUP_DETECT_ATTEMPTS   0
+#endif
+
+#define LWIP_IPV6_FRAG                  1
+
+/**
+ * aka Slirp mode.
+ */
+#define LWIP_CONNECTION_PROXY 1
+#define IP_FORWARD            1
+
+/* MEMP_NUM_SYS_TIMEOUT: the number of simultaneously active
+   timeouts. */
+#define MEMP_NUM_SYS_TIMEOUT    16
+
+
+/* this is required for IPv6 and IGMP needs */
+#define LWIP_RAND() RTRandU32()
+
+/* Debugging stuff. */
+#ifdef DEBUG
+# define LWIP_DEBUG
+# include "lwip-log.h"
+
+# define LWIP_PROXY_DEBUG LWIP_DBG_OFF
+#endif /* DEBUG */
+
+/* printf formatter definitions */
+#define U16_F "hu"
+#define S16_F "hd"
+#define X16_F "hx"
+#define U32_F "u"
+#define S32_F "d"
+#define X32_F "x"
+
+/* Redirect libc memory alloc functions to IPRT. */
+#define malloc(x) RTMemAlloc(x)
+#define realloc(x,y) RTMemRealloc((x), (y))
+#define free(x) RTMemFree(x)
+
+/* Align VBOX_STRICT and LWIP_NOASSERT. */
+#ifndef VBOX_STRICT
+# define LWIP_NOASSERT 1
+#endif
+
+#endif /* !VBOX_INCLUDED_SRC_NAT_lwipopts_h */
diff --git a/src/VBox/NetworkServices/NAT/mkrawsock.c b/src/VBox/NetworkServices/NAT/mkrawsock.c
new file mode 100644
index 00000000..50e9831f
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/mkrawsock.c
@@ -0,0 +1,349 @@
+/* $Id: mkrawsock.c $ */
+/** @file
+ * Auxiliary server to create raw-sockets when debugging unprivileged.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#ifdef __linux__
+#define _GNU_SOURCE
+#endif
+
+#ifdef __sun__
+#if __STDC_VERSION__ - 0 >= 199901L
+#define _XOPEN_SOURCE 600
+#else
+#define _XOPEN_SOURCE 500
+#endif
+#define __EXTENSIONS__ 1
+#endif
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <netinet/in.h>
+#ifdef __linux__
+#include <linux/icmp.h>         /* for ICMP_FILTER */
+#endif
+#include <errno.h>
+#include <fcntl.h>
+#include <pwd.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+
+static void handler(int sig);
+static void serve(int s);
+static int mkrawsock(int family);
+
+volatile sig_atomic_t signaled = 0;
+
+int
+main(int argc, char **argv)
+{
+    struct sigaction sa;
+    struct sockaddr_un sux; /* because solaris */
+    struct passwd *pw;
+    size_t pathlen;
+    char *slash;
+    int s, client;
+    int status;
+
+    memset(&sux, 0, sizeof(sux));
+    sux.sun_family = AF_UNIX;
+
+    if (getuid() == 0) {
+        if (argc != 2) {
+            fprintf(stderr, "username required when run as root\n");
+            return EXIT_FAILURE;
+        }
+
+        errno = 0;
+        pw = getpwnam(argv[1]);
+        if (pw == NULL) {
+            perror("getpwnam");
+            return EXIT_FAILURE;
+        }
+        if (pw->pw_uid == 0) {
+            fprintf(stderr, "%s is superuser\n", pw->pw_name);
+            return EXIT_FAILURE;
+        }
+    }
+    else {
+        errno = 0;
+        pw = getpwuid(getuid());
+        if (pw == NULL) {
+            perror("getpwuid");
+            return EXIT_FAILURE;
+        }
+    }
+
+    pathlen = snprintf(sux.sun_path, sizeof(sux.sun_path),
+                       "/tmp/.vbox-%s-aux/mkrawsock", pw->pw_name);
+    if (pathlen > sizeof(sux.sun_path)) {
+        fprintf(stderr, "socket pathname truncated\n");
+        return EXIT_FAILURE;
+    }
+
+    slash = strrchr(sux.sun_path, '/');
+    if (slash == NULL) {
+        fprintf(stderr, "%s: no directory separator\n", sux.sun_path);
+        return EXIT_FAILURE;
+    }
+
+    *slash = '\0';
+
+    status = mkdir(sux.sun_path, 0700);
+    if (status == 0) {
+        status = chown(sux.sun_path, pw->pw_uid, pw->pw_gid);
+        if (status < 0) {
+            perror("chown");
+            return EXIT_FAILURE;
+        }
+    }
+    else if (errno != EEXIST) {
+        perror("mkdir");
+        return EXIT_FAILURE;
+    }
+    else {
+        int dirfd;
+        struct stat st;
+
+        dirfd = open(sux.sun_path, O_RDONLY, O_DIRECTORY);
+        if (dirfd < 0) {
+            perror(sux.sun_path);
+            return EXIT_FAILURE;
+        }
+
+        status = fstat(dirfd, &st);
+        close(dirfd);
+
+        if (status < 0) {
+            perror(sux.sun_path);
+            return EXIT_FAILURE;
+        }
+
+        if (st.st_uid != pw->pw_uid) {
+            fprintf(stderr, "%s: exists but not owned by %s\n",
+                    sux.sun_path, pw->pw_name);
+            return EXIT_FAILURE;
+        }
+
+        if ((st.st_mode & 0777) != 0700) {
+            fprintf(stderr, "%s: bad mode %04o\n",
+                    sux.sun_path, (unsigned int)(st.st_mode & 0777));
+            return EXIT_FAILURE;
+        }
+    }
+
+    *slash = '/';
+
+#if 0
+    status = unlink(sux.sun_path);
+    if (status < 0 && errno != ENOENT) {
+        perror("unlink");
+    }
+#endif
+
+    s = socket(PF_UNIX, SOCK_STREAM, 0);
+    if (s < 0) {
+        perror("socket");
+        return EXIT_FAILURE;
+    }
+
+    status = bind(s, (struct sockaddr *)&sux,
+                  (sizeof(sux) - sizeof(sux.sun_path)
+                   + strlen(sux.sun_path) + 1));
+    if (status < 0) {
+        perror(sux.sun_path);
+        close(s);
+        return EXIT_FAILURE;
+    }
+
+    status = chown(sux.sun_path, pw->pw_uid, pw->pw_gid);
+    if (status < 0) {
+        perror("chown");
+        close(s);
+        return EXIT_FAILURE;
+    }
+
+    status = chmod(sux.sun_path, 0600);
+    if (status < 0) {
+        perror("chmod");
+        close(s);
+        return EXIT_FAILURE;
+    }
+
+    status = listen(s, 1);
+    if (status < 0) {
+        perror("listen");
+        close(s);
+        return EXIT_FAILURE;
+    }
+
+    memset(&sa, 0, sizeof(sa));
+    sa.sa_handler = handler;
+    sigemptyset(&sa.sa_mask);
+
+    sigaction(SIGINT,  &sa, NULL);
+    sigaction(SIGTERM, &sa, NULL);
+
+    while (!signaled) {
+        client = accept(s, NULL, 0);
+        if (client < 0) {
+            perror("accept");
+            continue;
+        }
+
+        serve(client);
+        close(client);
+    }
+
+    close(s);
+    status = unlink(sux.sun_path);
+    if (status < 0) {
+        perror("unlink");
+    }
+
+    return EXIT_SUCCESS;
+}
+
+
+static void
+handler(int sig)
+{
+    signaled = 1;
+}
+
+
+static void
+serve(int client)
+{
+#ifdef SO_PEERCRED
+    struct ucred cr;
+    socklen_t crlen;
+#endif
+    ssize_t nread, nsent;
+    struct msghdr mh;
+    struct iovec iov[1];
+    char buf[1];
+    struct cmsghdr *cmh;
+    char cmsg[CMSG_SPACE(sizeof(int))];
+    int fd;
+    int status;
+
+#ifdef SO_PEERCRED
+    crlen = sizeof(cr);
+    status = getsockopt(client, SOL_SOCKET, SO_PEERCRED, &cr, &crlen);
+    if (status < 0) {
+        perror("SO_PEERCRED");
+        return;
+    }
+
+    fprintf(stderr, "request from pid %lu uid %lu ",
+            (unsigned long)cr.pid, (unsigned long)cr.uid);
+#endif
+
+    nread = read(client, buf, 1);
+    if (nread < 0) {
+        perror("recv");
+        return;
+    }
+
+    fd = -1;
+    switch (buf[0]) {
+
+    case '4':
+        fprintf(stderr, "for ICMPv4 socket\n");
+        fd = mkrawsock(PF_INET);
+        break;
+
+    case '6':
+        fprintf(stderr, "for ICMPv6 socket\n");
+        fd = mkrawsock(PF_INET6);
+        break;
+
+    default:
+        fprintf(stderr, "bad request 0x%02x\n", (unsigned int)buf[0]);
+        return;
+    }
+
+    if (fd < 0) {
+        buf[0] = '\0';  /* NAK */
+        nsent = write(client, buf, 1);
+        (void)nsent;
+        return;
+    }
+
+    memset(&mh, 0, sizeof(mh));
+    memset(cmsg, 0, sizeof(cmsg));
+
+    iov[0].iov_base = buf;
+    iov[0].iov_len = 1;
+
+    mh.msg_iov = iov;
+    mh.msg_iovlen = 1;
+    mh.msg_control = cmsg;
+    mh.msg_controllen = sizeof(cmsg);
+
+    cmh = CMSG_FIRSTHDR(&mh);
+    cmh->cmsg_level = SOL_SOCKET;
+    cmh->cmsg_type = SCM_RIGHTS;
+    cmh->cmsg_len = CMSG_LEN(sizeof(fd));
+    *((int *) CMSG_DATA(cmh)) = fd;
+
+    nsent = sendmsg(client, &mh, 0);
+    if (nsent < 0) {
+        perror("sendmsg");
+    }
+
+    close(fd);
+}
+
+
+static int
+mkrawsock(int family)
+{
+    int fd;
+
+    if (family == PF_INET) {
+        fd = socket(PF_INET, SOCK_RAW, IPPROTO_ICMP);
+        if (fd < 0) {
+            perror("IPPROTO_ICMP");
+            return -1;
+        }
+    }
+    else {
+        fd = socket(PF_INET6, SOCK_RAW, IPPROTO_ICMPV6);
+        if (fd < 0) {
+            perror("IPPROTO_ICMPV6");
+            return -1;
+        }
+    }
+
+    return fd;
+}
diff --git a/src/VBox/NetworkServices/NAT/portfwd.c b/src/VBox/NetworkServices/NAT/portfwd.c
new file mode 100644
index 00000000..9e859944
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/portfwd.c
@@ -0,0 +1,273 @@
+/* $Id: portfwd.c $ */
+/** @file
+ * NAT Network - port-forwarding rules.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#define LOG_GROUP LOG_GROUP_NAT_SERVICE
+
+#include "winutils.h"
+#include "portfwd.h"
+
+#ifndef RT_OS_WINDOWS
+#include <arpa/inet.h>
+#include <netdb.h>
+#include <poll.h>
+#else
+# include "winpoll.h"
+#endif
+#include <stdio.h>
+#include <string.h>
+
+#include "proxy.h"
+#include "proxy_pollmgr.h"
+#include "pxremap.h"
+
+#include "lwip/netif.h"
+
+
+struct portfwd_msg {
+    struct fwspec *fwspec;
+    int add;
+};
+
+
+static int portfwd_chan_send(struct portfwd_msg *);
+static int portfwd_rule_add_del(struct fwspec *, int);
+static int portfwd_pmgr_chan(struct pollmgr_handler *, SOCKET, int);
+
+
+static struct pollmgr_handler portfwd_pmgr_chan_hdl;
+
+
+void
+portfwd_init(void)
+{
+    portfwd_pmgr_chan_hdl.callback = portfwd_pmgr_chan;
+    portfwd_pmgr_chan_hdl.data = NULL;
+    portfwd_pmgr_chan_hdl.slot = -1;
+    pollmgr_add_chan(POLLMGR_CHAN_PORTFWD, &portfwd_pmgr_chan_hdl);
+
+    /* add preconfigured forwarders */
+    fwtcp_init();
+    fwudp_init();
+}
+
+
+static int
+portfwd_chan_send(struct portfwd_msg *msg)
+{
+    ssize_t nsent;
+
+    nsent = pollmgr_chan_send(POLLMGR_CHAN_PORTFWD, &msg, sizeof(msg));
+    if (nsent < 0) {
+        free(msg);
+        return -1;
+    }
+
+    return 0;
+}
+
+
+static int
+portfwd_rule_add_del(struct fwspec *fwspec, int add)
+{
+    struct portfwd_msg *msg;
+
+    msg = (struct portfwd_msg *)malloc(sizeof(*msg));
+    if (msg == NULL) {
+        DPRINTF0(("%s: failed to allocate message\n", __func__));
+        return -1;
+    }
+
+    msg->fwspec = fwspec;
+    msg->add = add;
+
+    return portfwd_chan_send(msg);
+}
+
+
+int
+portfwd_rule_add(struct fwspec *fwspec)
+{
+    return portfwd_rule_add_del(fwspec, 1);
+}
+
+
+int
+portfwd_rule_del(struct fwspec *fwspec)
+{
+    return portfwd_rule_add_del(fwspec, 0);
+}
+
+
+/**
+ * POLLMGR_CHAN_PORTFWD handler.
+ */
+static int
+portfwd_pmgr_chan(struct pollmgr_handler *handler, SOCKET fd, int revents)
+{
+    void *ptr = pollmgr_chan_recv_ptr(handler, fd, revents);
+    struct portfwd_msg *msg = (struct portfwd_msg *)ptr;
+
+    if (msg->fwspec->stype == SOCK_STREAM) {
+        if (msg->add) {
+            fwtcp_add(msg->fwspec);
+        }
+        else {
+            fwtcp_del(msg->fwspec);
+        }
+    }
+    else { /* SOCK_DGRAM */
+        if (msg->add) {
+            fwudp_add(msg->fwspec);
+        }
+        else {
+            fwudp_del(msg->fwspec);
+        }
+    }
+
+    free(msg->fwspec);
+    free(msg);
+
+    return POLLIN;
+}
+
+
+int
+fwspec_set(struct fwspec *fwspec, int sdom, int stype,
+           const char *src_addr_str, uint16_t src_port,
+           const char *dst_addr_str, uint16_t dst_port)
+{
+    struct addrinfo hints;
+    struct addrinfo *ai;
+    int status;
+
+    LWIP_ASSERT1(sdom == PF_INET || sdom == PF_INET6);
+    LWIP_ASSERT1(stype == SOCK_STREAM || stype == SOCK_DGRAM);
+
+    fwspec->sdom = sdom;
+    fwspec->stype = stype;
+
+    memset(&hints, 0, sizeof(hints));
+    hints.ai_family = (sdom == PF_INET) ? AF_INET : AF_INET6;
+    hints.ai_socktype = stype;
+    hints.ai_flags = AI_NUMERICHOST;
+
+    status = getaddrinfo(src_addr_str, NULL, &hints, &ai);
+    if (status != 0) {
+        LogRel(("\"%s\": %s\n", src_addr_str, gai_strerror(status)));
+        return -1;
+    }
+    LWIP_ASSERT1(ai != NULL);
+    LWIP_ASSERT1(ai->ai_addrlen <= sizeof(fwspec->src));
+    memcpy(&fwspec->src, ai->ai_addr, ai->ai_addrlen);
+    freeaddrinfo(ai);
+    ai = NULL;
+
+    status = getaddrinfo(dst_addr_str, NULL, &hints, &ai);
+    if (status != 0) {
+        LogRel(("\"%s\": %s\n", dst_addr_str, gai_strerror(status)));
+        return -1;
+    }
+    LWIP_ASSERT1(ai != NULL);
+    LWIP_ASSERT1(ai->ai_addrlen <= sizeof(fwspec->dst));
+    memcpy(&fwspec->dst, ai->ai_addr, ai->ai_addrlen);
+    freeaddrinfo(ai);
+    ai = NULL;
+
+    if (sdom == PF_INET) {
+        fwspec->src.sin.sin_port = htons(src_port);
+        fwspec->dst.sin.sin_port = htons(dst_port);
+    }
+    else { /* PF_INET6 */
+        fwspec->src.sin6.sin6_port = htons(src_port);
+        fwspec->dst.sin6.sin6_port = htons(dst_port);
+    }
+
+    return 0;
+}
+
+
+int
+fwspec_equal(struct fwspec *a, struct fwspec *b)
+{
+    LWIP_ASSERT1(a != NULL);
+    LWIP_ASSERT1(b != NULL);
+
+    if (a->sdom != b->sdom || a->stype != b->stype) {
+        return 0;
+    }
+
+    if (a->sdom == PF_INET) {
+        return a->src.sin.sin_port == b->src.sin.sin_port
+            && a->dst.sin.sin_port == b->dst.sin.sin_port
+            && a->src.sin.sin_addr.s_addr == b->src.sin.sin_addr.s_addr
+            && a->dst.sin.sin_addr.s_addr == b->dst.sin.sin_addr.s_addr;
+    }
+    else { /* PF_INET6 */
+        return a->src.sin6.sin6_port == b->src.sin6.sin6_port
+            && a->dst.sin6.sin6_port == b->dst.sin6.sin6_port
+            && IN6_ARE_ADDR_EQUAL(&a->src.sin6.sin6_addr, &b->src.sin6.sin6_addr)
+            && IN6_ARE_ADDR_EQUAL(&a->dst.sin6.sin6_addr, &b->dst.sin6.sin6_addr);
+    }
+}
+
+
+/**
+ * Set fwdsrc to the IP address of the peer.
+ *
+ * For port-forwarded connections originating from hosts loopback the
+ * source address is set to the address of one of lwIP interfaces.
+ *
+ * Currently we only have one interface so there's not much logic
+ * here.  In the future we might need to additionally consult fwspec
+ * and routing table to determine which netif is used for connections
+ * to the specified guest.
+ */
+int
+fwany_ipX_addr_set_src(ipX_addr_t *fwdsrc, const struct sockaddr *peer)
+{
+    int mapping;
+
+    if (peer->sa_family == AF_INET) {
+        const struct sockaddr_in *peer4 = (const struct sockaddr_in *)peer;
+        ip_addr_t peerip4;
+
+        peerip4.addr = peer4->sin_addr.s_addr;
+        mapping = pxremap_inbound_ip4(&fwdsrc->ip4, &peerip4);
+    }
+    else if (peer->sa_family == AF_INET6) {
+        const struct sockaddr_in6 *peer6 = (const struct sockaddr_in6 *)peer;
+        ip6_addr_t peerip6;
+
+        memcpy(&peerip6, &peer6->sin6_addr, sizeof(ip6_addr_t));
+        mapping = pxremap_inbound_ip6(&fwdsrc->ip6, &peerip6);
+    }
+    else {
+        mapping = PXREMAP_FAILED;
+    }
+
+    return mapping;
+}
diff --git a/src/VBox/NetworkServices/NAT/portfwd.h b/src/VBox/NetworkServices/NAT/portfwd.h
new file mode 100644
index 00000000..47c3f817
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/portfwd.h
@@ -0,0 +1,84 @@
+/* $Id: portfwd.h $ */
+/** @file
+ * NAT Network - port-forwarding rules, definitions and declarations.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#ifndef VBOX_INCLUDED_SRC_NAT_portfwd_h
+#define VBOX_INCLUDED_SRC_NAT_portfwd_h
+#ifndef RT_WITHOUT_PRAGMA_ONCE
+# pragma once
+#endif
+
+#ifndef RT_OS_WINDOWS
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#endif
+
+#include "lwip/ip_addr.h"
+
+
+struct fwspec {
+    int sdom;                   /* PF_INET, PF_INET6 */
+    int stype;                  /* SOCK_STREAM, SOCK_DGRAM */
+
+    /* listen on */
+    union {
+        struct sockaddr sa;
+        struct sockaddr_in sin;   /* sdom == PF_INET  */
+        struct sockaddr_in6 sin6; /* sdom == PF_INET6 */
+    } src;
+
+    /* forward to */
+    union {
+        struct sockaddr sa;
+        struct sockaddr_in sin;   /* sdom == PF_INET  */
+        struct sockaddr_in6 sin6; /* sdom == PF_INET6 */
+    } dst;
+};
+
+
+void portfwd_init(void);
+int portfwd_rule_add(struct fwspec *);
+int portfwd_rule_del(struct fwspec *);
+
+
+int fwspec_set(struct fwspec *, int, int,
+               const char *, uint16_t,
+               const char *, uint16_t);
+
+int fwspec_equal(struct fwspec *, struct fwspec *);
+
+void fwtcp_init(void);
+void fwudp_init(void);
+
+void fwtcp_add(struct fwspec *);
+void fwtcp_del(struct fwspec *);
+void fwudp_add(struct fwspec *);
+void fwudp_del(struct fwspec *);
+
+int fwany_ipX_addr_set_src(ipX_addr_t *, const struct sockaddr *);
+
+#endif /* !VBOX_INCLUDED_SRC_NAT_portfwd_h */
diff --git a/src/VBox/NetworkServices/NAT/proxy.c b/src/VBox/NetworkServices/NAT/proxy.c
new file mode 100644
index 00000000..900eaf25
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/proxy.c
@@ -0,0 +1,746 @@
+/* $Id: proxy.c $ */
+/** @file
+ * NAT Network - proxy setup and utilities.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#define LOG_GROUP LOG_GROUP_NAT_SERVICE
+
+#include "winutils.h"
+
+#include "proxy.h"
+#include "proxy_pollmgr.h"
+#include "portfwd.h"
+
+#include "lwip/opt.h"
+
+#include "lwip/sys.h"
+#include "lwip/tcpip.h"
+
+#ifndef RT_OS_WINDOWS
+#include <sys/poll.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <netinet/tcp.h>
+#include <arpa/inet.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <iprt/string.h>
+#include <unistd.h>
+#include <err.h>
+#else
+# include <iprt/string.h>
+#endif
+
+#if defined(SOCK_NONBLOCK) && defined(RT_OS_NETBSD) /* XXX: PR kern/47569 */
+# undef SOCK_NONBLOCK
+#endif
+
+#ifndef __arraycount
+# define __arraycount(a) (sizeof(a)/sizeof(a[0]))
+#endif
+
+static FNRTSTRFORMATTYPE proxy_sockerr_rtstrfmt;
+
+static SOCKET proxy_create_socket(int, int);
+
+volatile struct proxy_options *g_proxy_options;
+static sys_thread_t pollmgr_tid;
+
+/* XXX: for mapping loopbacks to addresses in our network (ip4) */
+struct netif *g_proxy_netif;
+
+
+/*
+ * Called on the lwip thread (aka tcpip thread) from tcpip_init() via
+ * its "tcpip_init_done" callback.  Raw API is ok to use here
+ * (e.g. rtadvd), but netconn API is not.
+ */
+void
+proxy_init(struct netif *proxy_netif, struct proxy_options *opts)
+{
+    int status;
+
+    LWIP_ASSERT1(opts != NULL);
+    LWIP_UNUSED_ARG(proxy_netif);
+
+    status = RTStrFormatTypeRegister("sockerr", proxy_sockerr_rtstrfmt, NULL);
+    AssertRC(status);
+
+    g_proxy_options = opts;
+    g_proxy_netif = proxy_netif;
+
+#if 1
+    proxy_rtadvd_start(proxy_netif);
+#endif
+
+    /*
+     * XXX: We use stateless DHCPv6 only to report IPv6 address(es) of
+     * nameserver(s).  Since we don't yet support IPv6 addresses in
+     * HostDnsService, there's no point in running DHCPv6.
+     */
+#if 0
+    dhcp6ds_init(proxy_netif);
+#endif
+
+    if (opts->tftp_root != NULL) {
+        tftpd_init(proxy_netif, opts->tftp_root);
+    }
+
+    status = pollmgr_init();
+    if (status < 0) {
+        errx(EXIT_FAILURE, "failed to initialize poll manager");
+        /* NOTREACHED */
+    }
+
+    pxtcp_init();
+    pxudp_init();
+
+    portfwd_init();
+
+    pxdns_init(proxy_netif);
+
+    pxping_init(proxy_netif, opts->icmpsock4, opts->icmpsock6);
+
+    pollmgr_tid = sys_thread_new("pollmgr_thread",
+                                 pollmgr_thread, NULL,
+                                 DEFAULT_THREAD_STACKSIZE,
+                                 DEFAULT_THREAD_PRIO);
+    if (!pollmgr_tid) {
+        errx(EXIT_FAILURE, "failed to create poll manager thread");
+        /* NOTREACHED */
+    }
+}
+
+
+#if !defined(RT_OS_WINDOWS)
+/**
+ * Formatter for %R[sockerr] - unix strerror_r() version.
+ */
+static DECLCALLBACK(size_t)
+proxy_sockerr_rtstrfmt(PFNRTSTROUTPUT pfnOutput, void *pvArgOutput,
+                       const char *pszType, const void *pvValue,
+                       int cchWidth, int cchPrecision, unsigned int fFlags,
+                       void *pvUser)
+{
+    const int error = (int)(intptr_t)pvValue;
+
+    const char *msg;
+    char buf[128];
+
+    NOREF(cchWidth);
+    NOREF(cchPrecision);
+    NOREF(fFlags);
+    NOREF(pvUser);
+
+    AssertReturn(strcmp(pszType, "sockerr") == 0, 0);
+
+    /* make sure return type mismatch is caught */
+    buf[0] = '\0';
+#if defined(RT_OS_LINUX) && defined(_GNU_SOURCE)
+    msg = strerror_r(error, buf, sizeof(buf));
+#else
+    strerror_r(error, buf, sizeof(buf));
+    msg = buf;
+#endif
+    return RTStrFormat(pfnOutput, pvArgOutput, NULL, NULL, "%s", msg);
+}
+
+#else /* RT_OS_WINDOWS */
+
+/**
+ * Formatter for %R[sockerr] - windows FormatMessage() version.
+ */
+static DECLCALLBACK(size_t)
+proxy_sockerr_rtstrfmt(PFNRTSTROUTPUT pfnOutput, void *pvArgOutput,
+                       const char *pszType, const void *pvValue,
+                       int cchWidth, int cchPrecision, unsigned int fFlags,
+                       void *pvUser)
+{
+    const int error = (int)(intptr_t)pvValue;
+    size_t cb = 0;
+
+    NOREF(cchWidth);
+    NOREF(cchPrecision);
+    NOREF(fFlags);
+    NOREF(pvUser);
+
+    AssertReturn(strcmp(pszType, "sockerr") == 0, 0);
+
+    /*
+     * XXX: Windows strerror() doesn't handle posix error codes, but
+     * since winsock uses its own, it shouldn't be much of a problem.
+     * If you see a strange error message, it's probably from
+     * FormatMessage() for an error from <WinError.h> that has the
+     * same numeric value.
+     */
+    if (error < _sys_nerr) {
+        char buf[128] = "";
+        int status;
+
+        status = strerror_s(buf, sizeof(buf), error);
+        if (status == 0) {
+            if (strcmp(buf, "Unknown error") == 0) {
+                /* windows strerror() doesn't add the numeric value */
+                cb += RTStrFormat(pfnOutput, pvArgOutput, NULL, NULL,
+                                  "Unknown error: %d", error);
+            }
+            else {
+                cb += RTStrFormat(pfnOutput, pvArgOutput, NULL, NULL,
+                                  "%s", buf);
+            }
+        }
+        else {
+            cb += RTStrFormat(pfnOutput, pvArgOutput, NULL, NULL,
+                              "Unknown error: %d", error);
+        }
+    }
+    else {
+        DWORD nchars;
+        char *msg = NULL;
+
+        nchars = FormatMessageA(FORMAT_MESSAGE_FROM_SYSTEM
+                                | FORMAT_MESSAGE_ALLOCATE_BUFFER,
+                                NULL, error, LANG_NEUTRAL,
+                                (LPSTR)&msg, 0,
+                                NULL);
+        if (nchars == 0 || msg == NULL) {
+            cb += RTStrFormat(pfnOutput, pvArgOutput, NULL, NULL,
+                              "Unknown error: %d", error);
+        }
+        else {
+            /* FormatMessage() "helpfully" adds newline; get rid of it */
+            char *crpos = strchr(msg, '\r');
+            if (crpos != NULL) {
+                *crpos = '\0';
+            }
+
+            cb += RTStrFormat(pfnOutput, pvArgOutput, NULL, NULL,
+                              "%s", msg);
+        }
+
+        if (msg != NULL) {
+            LocalFree(msg);
+        }
+    }
+
+    return cb;
+}
+#endif /* RT_OS_WINDOWS */
+
+
+/**
+ * Send static callback message from poll manager thread to lwip
+ * thread, scheduling a function call in lwip thread context.
+ *
+ * XXX: Existing lwip api only provides non-blocking version for this.
+ * It may fail when lwip thread is not running (mbox invalid) or if
+ * post failed (mbox full).  How to handle these?
+ */
+void
+proxy_lwip_post(struct tcpip_msg *msg)
+{
+    struct tcpip_callback_msg *m;
+    err_t error;
+
+    LWIP_ASSERT1(msg != NULL);
+
+    /*
+     * lwip plays games with fake incomplete struct tag to enforce API
+     */
+    m = (struct tcpip_callback_msg *)msg;
+    error = tcpip_callbackmsg(m);
+
+    if (error == ERR_VAL) {
+        /* XXX: lwip thread is not running (mbox invalid) */
+        LWIP_ASSERT1(error != ERR_VAL);
+    }
+
+    LWIP_ASSERT1(error == ERR_OK);
+}
+
+
+/**
+ * Create a non-blocking socket.  Disable SIGPIPE for TCP sockets if
+ * possible.  On Linux it's not possible and should be disabled for
+ * each send(2) individually.
+ */
+static SOCKET
+proxy_create_socket(int sdom, int stype)
+{
+    SOCKET s;
+    int stype_and_flags;
+    int status;
+
+    LWIP_UNUSED_ARG(status);    /* depends on ifdefs */
+
+
+    stype_and_flags = stype;
+
+#if defined(SOCK_NONBLOCK)
+    stype_and_flags |= SOCK_NONBLOCK;
+#endif
+
+    /*
+     * Disable SIGPIPE on disconnected socket.  It might be easier to
+     * forgo it and just use MSG_NOSIGNAL on each send*(2), since we
+     * have to do it for Linux anyway, but Darwin does NOT have that
+     * flag (but has SO_NOSIGPIPE socket option).
+     */
+#if !defined(SOCK_NOSIGPIPE) && !defined(SO_NOSIGPIPE) && !defined(MSG_NOSIGNAL)
+#if 0 /* XXX: Solaris has neither, the program should ignore SIGPIPE globally */
+#error Need a way to disable SIGPIPE on connection oriented sockets!
+#endif
+#endif
+
+#if defined(SOCK_NOSIGPIPE)
+    if (stype == SOCK_STREAM) {
+        stype_and_flags |= SOCK_NOSIGPIPE;
+    }
+#endif
+
+    s = socket(sdom, stype_and_flags, 0);
+    if (s == INVALID_SOCKET) {
+        DPRINTF(("socket: %R[sockerr]\n", SOCKERRNO()));
+        return INVALID_SOCKET;
+    }
+
+#if defined(RT_OS_WINDOWS)
+    {
+        u_long mode = 1;
+        status = ioctlsocket(s, FIONBIO, &mode);
+        if (status == SOCKET_ERROR) {
+            DPRINTF(("FIONBIO: %R[sockerr]\n", SOCKERRNO()));
+            closesocket(s);
+            return INVALID_SOCKET;
+        }
+    }
+#elif !defined(SOCK_NONBLOCK)
+    {
+        int sflags;
+
+        sflags = fcntl(s, F_GETFL, 0);
+        if (sflags < 0) {
+            DPRINTF(("F_GETFL: %R[sockerr]\n", SOCKERRNO()));
+            closesocket(s);
+            return INVALID_SOCKET;
+        }
+
+        status = fcntl(s, F_SETFL, sflags | O_NONBLOCK);
+        if (status < 0) {
+            DPRINTF(("O_NONBLOCK: %R[sockerr]\n", SOCKERRNO()));
+            closesocket(s);
+            return INVALID_SOCKET;
+        }
+    }
+#endif
+
+#if !defined(SOCK_NOSIGPIPE) && defined(SO_NOSIGPIPE)
+    if (stype == SOCK_STREAM) {
+        int on = 1;
+        const socklen_t onlen = sizeof(on);
+
+        status = setsockopt(s, SOL_SOCKET, SO_NOSIGPIPE, &on, onlen);
+        if (status < 0) {
+            DPRINTF(("SO_NOSIGPIPE: %R[sockerr]\n", SOCKERRNO()));
+            closesocket(s);
+            return INVALID_SOCKET;
+        }
+    }
+#endif
+
+    /*
+     * Disable the Nagle algorithm. Otherwise the host may hold back
+     * packets that the guest wants to go out, causing potentially
+     * horrible performance. The guest is already applying the Nagle
+     * algorithm (or not) the way it wants.
+     */
+    if (stype == SOCK_STREAM) {
+        int on = 1;
+        const socklen_t onlen = sizeof(on);
+
+        status = setsockopt(s, IPPROTO_TCP, TCP_NODELAY, (char *)&on, onlen);
+        if (status < 0) {
+            DPRINTF(("TCP_NODELAY: %R[sockerr]\n", SOCKERRNO()));
+        }
+    }
+
+#if defined(RT_OS_WINDOWS)
+    /*
+     * lwIP only holds one packet of "refused data" for us.  Proxy
+     * relies on OS socket send buffer and doesn't do its own
+     * buffering.  Unfortunately on Windows send buffer is very small
+     * (8K by default) and is not dynamically adpated by the OS it
+     * seems.  So a single large write will fill it up and that will
+     * make lwIP drop segments, causing guest TCP into pathologic
+     * resend patterns.  As a quick and dirty fix just bump it up.
+     */
+    if (stype == SOCK_STREAM) {
+        int sndbuf;
+        socklen_t optlen = sizeof(sndbuf);
+
+        status = getsockopt(s, SOL_SOCKET, SO_SNDBUF, (char *)&sndbuf, &optlen);
+        if (status == 0) {
+            if (sndbuf < 64 * 1024) {
+                sndbuf = 64 * 1024;
+                status = setsockopt(s, SOL_SOCKET, SO_SNDBUF,
+                                    (char *)&sndbuf, optlen);
+                if (status != 0) {
+                    DPRINTF(("SO_SNDBUF: setsockopt: %R[sockerr]\n", SOCKERRNO()));
+                }
+            }
+        }
+        else {
+            DPRINTF(("SO_SNDBUF: getsockopt: %R[sockerr]\n", SOCKERRNO()));
+        }
+    }
+#endif
+
+    return s;
+}
+
+
+#ifdef RT_OS_LINUX
+/**
+ * Fixup a socket returned by accept(2).
+ *
+ * On Linux a socket returned by accept(2) does NOT inherit the socket
+ * options from the listening socket!  We need to repeat parts of the
+ * song and dance we did above to make it non-blocking.
+ */
+int
+proxy_fixup_accepted_socket(SOCKET s)
+{
+    int sflags;
+    int status;
+
+    sflags = fcntl(s, F_GETFL, 0);
+    if (sflags < 0) {
+        DPRINTF(("F_GETFL: %R[sockerr]\n", SOCKERRNO()));
+        return -1;
+    }
+
+    status = fcntl(s, F_SETFL, sflags | O_NONBLOCK);
+    if (status < 0) {
+        DPRINTF(("O_NONBLOCK: %R[sockerr]\n", SOCKERRNO()));
+        return -1;
+    }
+
+    return 0;
+}
+#endif  /* RT_OS_LINUX */
+
+
+/**
+ * Create a socket for outbound connection to dst_addr:dst_port.
+ *
+ * The socket is non-blocking and TCP sockets has SIGPIPE disabled if
+ * possible.  On Linux it's not possible and should be disabled for
+ * each send(2) individually.
+ */
+SOCKET
+proxy_connected_socket(int sdom, int stype,
+                       ipX_addr_t *dst_addr, u16_t dst_port)
+{
+    struct sockaddr_in6 dst_sin6;
+    struct sockaddr_in dst_sin;
+    struct sockaddr *pdst_sa;
+    socklen_t dst_sa_len;
+    void *pdst_addr;
+    const struct sockaddr *psrc_sa;
+    socklen_t src_sa_len;
+    int status;
+    int sockerr;
+    SOCKET s;
+
+    LWIP_ASSERT1(sdom == PF_INET || sdom == PF_INET6);
+    LWIP_ASSERT1(stype == SOCK_STREAM || stype == SOCK_DGRAM);
+
+    DPRINTF(("---> %s ", stype == SOCK_STREAM ? "TCP" : "UDP"));
+    if (sdom == PF_INET6) {
+        pdst_sa = (struct sockaddr *)&dst_sin6;
+        pdst_addr = (void *)&dst_sin6.sin6_addr;
+
+        memset(&dst_sin6, 0, sizeof(dst_sin6));
+#if HAVE_SA_LEN
+        dst_sin6.sin6_len =
+#endif
+            dst_sa_len = sizeof(dst_sin6);
+        dst_sin6.sin6_family = AF_INET6;
+        memcpy(&dst_sin6.sin6_addr, &dst_addr->ip6, sizeof(ip6_addr_t));
+        dst_sin6.sin6_port = htons(dst_port);
+
+        DPRINTF(("[%RTnaipv6]:%d ", &dst_sin6.sin6_addr, dst_port));
+    }
+    else { /* sdom = PF_INET */
+        pdst_sa = (struct sockaddr *)&dst_sin;
+        pdst_addr = (void *)&dst_sin.sin_addr;
+
+        memset(&dst_sin, 0, sizeof(dst_sin));
+#if HAVE_SA_LEN
+        dst_sin.sin_len =
+#endif
+            dst_sa_len = sizeof(dst_sin);
+        dst_sin.sin_family = AF_INET;
+        dst_sin.sin_addr.s_addr = dst_addr->ip4.addr; /* byte-order? */
+        dst_sin.sin_port = htons(dst_port);
+
+        DPRINTF(("%RTnaipv4:%d ", dst_sin.sin_addr.s_addr, dst_port));
+    }
+
+    s = proxy_create_socket(sdom, stype);
+    if (s == INVALID_SOCKET) {
+        return INVALID_SOCKET;
+    }
+    DPRINTF(("socket %d\n", s));
+
+    /** @todo needs locking if dynamic modifyvm is allowed */
+    if (sdom == PF_INET6) {
+        psrc_sa = (const struct sockaddr *)g_proxy_options->src6;
+        src_sa_len = sizeof(struct sockaddr_in6);
+    }
+    else {
+        psrc_sa = (const struct sockaddr *)g_proxy_options->src4;
+        src_sa_len = sizeof(struct sockaddr_in);
+    }
+    if (psrc_sa != NULL) {
+        status = bind(s, psrc_sa, src_sa_len);
+        if (status == SOCKET_ERROR) {
+            sockerr = SOCKERRNO();
+            DPRINTF(("socket %d: bind: %R[sockerr]\n", s, sockerr));
+            closesocket(s);
+            SET_SOCKERRNO(sockerr);
+            return INVALID_SOCKET;
+        }
+    }
+
+    status = connect(s, pdst_sa, dst_sa_len);
+    if (status == SOCKET_ERROR
+#if !defined(RT_OS_WINDOWS)
+        && SOCKERRNO() != EINPROGRESS
+#else
+        && SOCKERRNO() != EWOULDBLOCK
+#endif
+        )
+    {
+        sockerr = SOCKERRNO();
+        DPRINTF(("socket %d: connect: %R[sockerr]\n", s, sockerr));
+        closesocket(s);
+        SET_SOCKERRNO(sockerr);
+        return INVALID_SOCKET;
+    }
+
+    return s;
+}
+
+
+/**
+ * Create a socket for inbound (port-forwarded) connections to
+ * src_addr (port is part of sockaddr, so not a separate argument).
+ *
+ * The socket is non-blocking and TCP sockets has SIGPIPE disabled if
+ * possible.  On Linux it's not possible and should be disabled for
+ * each send(2) individually.
+ *
+ * TODO?: Support v6-mapped v4 so that user can specify she wants
+ * "udp" and get both versions?
+ */
+SOCKET
+proxy_bound_socket(int sdom, int stype, struct sockaddr *src_addr)
+{
+    SOCKET s;
+    int on;
+    const socklen_t onlen = sizeof(on);
+    int status;
+    int sockerr;
+
+    s = proxy_create_socket(sdom, stype);
+    if (s == INVALID_SOCKET) {
+        return INVALID_SOCKET;
+    }
+    DPRINTF(("socket %d\n", s));
+
+    on = 1;
+    status = setsockopt(s, SOL_SOCKET, SO_REUSEADDR, (char *)&on, onlen);
+    if (status < 0) {           /* not good, but not fatal */
+        DPRINTF(("SO_REUSEADDR: %R[sockerr]\n", SOCKERRNO()));
+    }
+
+    status = bind(s, src_addr,
+                  sdom == PF_INET ?
+                    sizeof(struct sockaddr_in)
+                  : sizeof(struct sockaddr_in6));
+    if (status == SOCKET_ERROR) {
+        sockerr = SOCKERRNO();
+        DPRINTF(("bind: %R[sockerr]\n", sockerr));
+        closesocket(s);
+        SET_SOCKERRNO(sockerr);
+        return INVALID_SOCKET;
+    }
+
+    if (stype == SOCK_STREAM) {
+        status = listen(s, 5);
+        if (status == SOCKET_ERROR) {
+            sockerr = SOCKERRNO();
+            DPRINTF(("listen: %R[sockerr]\n", sockerr));
+            closesocket(s);
+            SET_SOCKERRNO(sockerr);
+            return INVALID_SOCKET;
+        }
+    }
+
+    return s;
+}
+
+
+void
+proxy_reset_socket(SOCKET s)
+{
+    struct linger linger;
+
+    linger.l_onoff = 1;
+    linger.l_linger = 0;
+
+    /* On Windows we can run into issue here, perhaps SO_LINGER isn't enough, and
+     * we should use WSA{Send,Recv}Disconnect instead.
+     *
+     * Links for the reference:
+     * http://msdn.microsoft.com/en-us/library/windows/desktop/ms738547%28v=vs.85%29.aspx
+     * http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4468997
+     */
+    setsockopt(s, SOL_SOCKET, SO_LINGER, (char *)&linger, sizeof(linger));
+
+    closesocket(s);
+}
+
+
+int
+proxy_sendto(SOCKET sock, struct pbuf *p, void *name, size_t namelen)
+{
+    struct pbuf *q;
+    size_t i, clen;
+#ifndef RT_OS_WINDOWS
+    struct msghdr mh;
+    ssize_t nsent;
+#else
+    DWORD nsent;
+#endif
+    int rc;
+    IOVEC fixiov[8];     /* fixed size (typical case) */
+    const size_t fixiovsize = sizeof(fixiov)/sizeof(fixiov[0]);
+    IOVEC *dyniov;       /* dynamically sized */
+    IOVEC *iov;
+    int error = 0;
+
+    /*
+     * Static iov[] is usually enough since UDP protocols use small
+     * datagrams to avoid fragmentation, but be prepared.
+     */
+    clen = pbuf_clen(p);
+    if (clen > fixiovsize) {
+        /*
+         * XXX: TODO: check that clen is shorter than IOV_MAX
+         */
+        dyniov = (IOVEC *)malloc(clen * sizeof(*dyniov));
+        if (dyniov == NULL) {
+            error = -errno;     /* sic: not a socket error */
+            goto out;
+        }
+        iov = dyniov;
+    }
+    else {
+        dyniov = NULL;
+        iov = fixiov;
+    }
+
+
+    for (q = p, i = 0; i < clen; q = q->next, ++i) {
+        LWIP_ASSERT1(q != NULL);
+
+        IOVEC_SET_BASE(iov[i], q->payload);
+        IOVEC_SET_LEN(iov[i], q->len);
+    }
+
+#ifndef RT_OS_WINDOWS
+    memset(&mh, 0, sizeof(mh));
+    mh.msg_name = name;
+    mh.msg_namelen = namelen;
+    mh.msg_iov = iov;
+    mh.msg_iovlen = clen;
+
+    nsent = sendmsg(sock, &mh, 0);
+    rc = (nsent >= 0) ? 0 : SOCKET_ERROR;
+#else
+    rc = WSASendTo(sock, iov, (DWORD)clen, &nsent, 0,
+                   name, (int)namelen, NULL, NULL);
+#endif
+    if (rc == SOCKET_ERROR) {
+        error = SOCKERRNO();
+        DPRINTF(("%s: socket %d: sendmsg: %R[sockerr]\n",
+                 __func__, sock, error));
+        error = -error;
+    }
+
+  out:
+    if (dyniov != NULL) {
+        free(dyniov);
+    }
+    return error;
+}
+
+
+static const char *lwiperr[] = {
+    "ERR_OK",
+    "ERR_MEM",
+    "ERR_BUF",
+    "ERR_TIMEOUT",
+    "ERR_RTE",
+    "ERR_INPROGRESS",
+    "ERR_VAL",
+    "ERR_WOULDBLOCK",
+    "ERR_USE",
+    "ERR_ISCONN",
+    "ERR_ABRT",
+    "ERR_RST",
+    "ERR_CLSD",
+    "ERR_CONN",
+    "ERR_ARG",
+    "ERR_IF"
+};
+
+
+const char *
+proxy_lwip_strerr(err_t error)
+{
+    static char buf[32];
+    int e = -error;
+
+    if (0 <= e && e < (int)__arraycount(lwiperr)) {
+        return lwiperr[e];
+    }
+    else {
+        RTStrPrintf(buf, sizeof(buf), "unknown error %d", error);
+        return buf;
+    }
+}
diff --git a/src/VBox/NetworkServices/NAT/proxy.h b/src/VBox/NetworkServices/NAT/proxy.h
new file mode 100644
index 00000000..7da34e30
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/proxy.h
@@ -0,0 +1,137 @@
+/* $Id: proxy.h $ */
+/** @file
+ * NAT Network - common definitions and declarations.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#ifndef VBOX_INCLUDED_SRC_NAT_proxy_h
+#define VBOX_INCLUDED_SRC_NAT_proxy_h
+#ifndef RT_WITHOUT_PRAGMA_ONCE
+# pragma once
+#endif
+
+#if !defined(VBOX)
+#include "vbox-compat.h"
+#endif
+
+#include "lwip/err.h"
+#include "lwip/ip_addr.h"
+#include "winutils.h"
+
+/* forward */
+struct netif;
+struct tcpip_msg;
+struct pbuf;
+struct sockaddr;
+struct sockaddr_in;
+struct sockaddr_in6;
+
+struct ip4_lomap
+{
+    ip_addr_t loaddr;
+    uint32_t off;
+};
+
+struct ip4_lomap_desc
+{
+    const struct ip4_lomap *lomap;
+    unsigned int num_lomap;
+};
+
+struct proxy_options {
+    ip_addr_t ipv4_addr;
+    ip_addr_t ipv4_mask;
+    ip6_addr_t ipv6_addr;
+    int ipv6_enabled;
+    int ipv6_defroute;
+    SOCKET icmpsock4;
+    SOCKET icmpsock6;
+    const char *tftp_root;
+    const struct sockaddr_in *src4;
+    const struct sockaddr_in6 *src6;
+    const struct ip4_lomap_desc *lomap_desc;
+    const char **nameservers;
+};
+
+extern volatile struct proxy_options *g_proxy_options;
+extern struct netif *g_proxy_netif;
+
+void proxy_init(struct netif *, struct proxy_options *);
+SOCKET proxy_connected_socket(int, int, ipX_addr_t *, u16_t);
+SOCKET proxy_bound_socket(int, int, struct sockaddr *);
+#ifdef RT_OS_LINUX
+int proxy_fixup_accepted_socket(SOCKET);
+#endif
+void proxy_reset_socket(SOCKET);
+int proxy_sendto(SOCKET, struct pbuf *, void *, size_t);
+void proxy_lwip_post(struct tcpip_msg *);
+const char *proxy_lwip_strerr(err_t);
+
+/* proxy_rtadvd.c */
+void proxy_rtadvd_start(struct netif *);
+void proxy_rtadvd_do_quick(void *);
+
+/* rtmon_*.c */
+int rtmon_get_defaults(void);
+
+/* proxy_dhcp6ds.c */
+err_t dhcp6ds_init(struct netif *);
+
+/* proxy_tftpd.c */
+err_t tftpd_init(struct netif *, const char *);
+
+/* pxtcp.c */
+void pxtcp_init(void);
+
+/* pxudp.c */
+void pxudp_init(void);
+
+/* pxdns.c */
+err_t pxdns_init(struct netif *);
+void pxdns_set_nameservers(void *);
+
+/* pxping.c */
+err_t pxping_init(struct netif *, SOCKET, SOCKET);
+
+
+#if defined(RT_OS_LINUX) || defined(RT_OS_SOLARIS) || defined(RT_OS_WINDOWS)
+# define HAVE_SA_LEN 0
+#else
+# define HAVE_SA_LEN 1
+#endif
+
+#define LWIP_ASSERT1(condition) LWIP_ASSERT(#condition, condition)
+
+/*
+ * TODO: DPRINTF0 should probably become LogRel but its usage needs to
+ * be cleaned up a bit before.
+ */
+#define DPRINTF0(a) Log(a)
+
+#define DPRINTF(a)  DPRINTF1(a)
+#define DPRINTF1(a) Log2(a)
+#define DPRINTF2(a) Log3(a)
+
+#endif /* !VBOX_INCLUDED_SRC_NAT_proxy_h */
+
diff --git a/src/VBox/NetworkServices/NAT/proxy_dhcp6ds.c b/src/VBox/NetworkServices/NAT/proxy_dhcp6ds.c
new file mode 100644
index 00000000..a42629f7
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/proxy_dhcp6ds.c
@@ -0,0 +1,327 @@
+/* $Id: proxy_dhcp6ds.c $ */
+/** @file
+ * NAT Network - Simple stateless DHCPv6 (RFC 3736) server.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#define LOG_GROUP LOG_GROUP_NAT_SERVICE
+
+#include "winutils.h"
+#include "dhcp6.h"
+#include "proxy.h"
+
+#include <string.h>
+
+#include "lwip/opt.h"
+#include "lwip/mld6.h"
+#include "lwip/udp.h"
+
+
+static void dhcp6ds_recv(void *, struct udp_pcb *, struct pbuf *, ip6_addr_t *, u16_t);
+
+
+/* ff02::1:2 - "All_DHCP_Relay_Agents_and_Servers" link-scoped multicast */
+static /* const */ ip6_addr_t all_dhcp_relays_and_servers = {
+    { PP_HTONL(0xff020000UL), 0, 0, PP_HTONL(0x00010002UL) }
+};
+
+/* ff05::1:3 - "All_DHCP_Servers" site-scoped multicast */
+static /* const */ ip6_addr_t all_dhcp_servers = {
+    { PP_HTONL(0xff050000UL), 0, 0, PP_HTONL(0x00010003UL) }
+};
+
+
+static struct udp_pcb *dhcp6ds_pcb;
+
+/* prebuilt Server ID option */
+#define DUID_LL_LEN (/* duid type */ 2 + /* hw type */ 2 + /* ether addr */ 6)
+static u8_t dhcp6ds_serverid[/* opt */ 2 + /* optlen */ 2 + DUID_LL_LEN];
+
+/* prebuilt DNS Servers option */
+static u8_t dhcp6ds_dns[/* opt */ 2 + /* optlen */ 2 + /* IPv6 addr */ 16];
+
+
+/**
+ * Initialize DHCP6 server.
+ *
+ * Join DHCP6 multicast groups.
+ * Create and bind server pcb.
+ * Prebuild fixed parts of reply.
+ */
+err_t
+dhcp6ds_init(struct netif *proxy_netif)
+{
+    ip6_addr_t *pxaddr, *pxaddr_nonlocal;
+    int i;
+    err_t error;
+
+    LWIP_ASSERT1(proxy_netif != NULL);
+    LWIP_ASSERT1(proxy_netif->hwaddr_len == 6); /* ethernet */
+
+    pxaddr = netif_ip6_addr(proxy_netif, 0); /* link local */
+
+    /*
+     * XXX: TODO: This is a leftover from testing with IPv6 mapped
+     * loopback with a special IPv6->IPv4 mapping hack in pxudp.c
+     */
+    /* advertise ourself as DNS resolver - will be proxied to host */
+    pxaddr_nonlocal = NULL;
+    for (i = 1; i < LWIP_IPV6_NUM_ADDRESSES; ++i) {
+        if (ip6_addr_ispreferred(netif_ip6_addr_state(proxy_netif, i))
+            && !ip6_addr_islinklocal(netif_ip6_addr(proxy_netif, i)))
+        {
+            pxaddr_nonlocal = netif_ip6_addr(proxy_netif, i);
+            break;
+        }
+    }
+    LWIP_ASSERT1(pxaddr_nonlocal != NULL); /* must be configured on the netif */
+
+
+    error = mld6_joingroup(pxaddr, &all_dhcp_relays_and_servers);
+    if (error != ERR_OK) {
+        DPRINTF0(("%s: failed to join All_DHCP_Relay_Agents_and_Servers: %s\n",
+                  __func__, proxy_lwip_strerr(error)));
+        goto err;
+    }
+
+    error = mld6_joingroup(pxaddr, &all_dhcp_servers);
+    if (error != ERR_OK) {
+        DPRINTF0(("%s: failed to join All_DHCP_Servers: %s\n",
+                  __func__, proxy_lwip_strerr(error)));
+        goto err1;
+    }
+
+
+    dhcp6ds_pcb = udp_new_ip6();
+    if (dhcp6ds_pcb == NULL) {
+        DPRINTF0(("%s: failed to allocate PCB\n", __func__));
+        error = ERR_MEM;
+        goto err2;
+    }
+
+    udp_recv_ip6(dhcp6ds_pcb, dhcp6ds_recv, NULL);
+
+    error = udp_bind_ip6(dhcp6ds_pcb, pxaddr, DHCP6_SERVER_PORT);
+    if (error != ERR_OK) {
+        DPRINTF0(("%s: failed to bind PCB\n", __func__));
+        goto err3;
+    }
+
+
+#define OPT_SET(buf, off, c) do {                       \
+        u16_t _s = PP_HTONS(c);                         \
+        memcpy(&(buf)[off], &_s, sizeof(u16_t));        \
+    } while (0)
+
+#define SERVERID_SET(off, c)    OPT_SET(dhcp6ds_serverid, (off), (c))
+#define DNSSRV_SET(off, c)      OPT_SET(dhcp6ds_dns, (off), (c))
+
+    SERVERID_SET(0, DHCP6_OPTION_SERVERID);
+    SERVERID_SET(2, DUID_LL_LEN);
+    SERVERID_SET(4, DHCP6_DUID_LL);
+    SERVERID_SET(6, ARES_HRD_ETHERNET);
+    memcpy(&dhcp6ds_serverid[8], proxy_netif->hwaddr, 6);
+
+    DNSSRV_SET(0, DHCP6_OPTION_DNS_SERVERS);
+    DNSSRV_SET(2, 16);          /* one IPv6 address */
+    /*
+     * XXX: TODO: This is a leftover from testing with IPv6 mapped
+     * loopback with a special IPv6->IPv4 mapping hack in pxudp.c
+     */
+    memcpy(&dhcp6ds_dns[4], pxaddr_nonlocal, sizeof(ip6_addr_t));
+
+#undef SERVERID_SET
+#undef DNSSRV_SET
+
+    return ERR_OK;
+
+
+  err3:
+    udp_remove(dhcp6ds_pcb);
+    dhcp6ds_pcb = NULL;
+  err2:
+    mld6_leavegroup(pxaddr, &all_dhcp_servers);
+  err1:
+    mld6_leavegroup(pxaddr, &all_dhcp_relays_and_servers);
+  err:
+    return error;
+}
+
+
+static u8_t dhcp6ds_reply_buf[1024];
+
+static void
+dhcp6ds_recv(void *arg, struct udp_pcb *pcb, struct pbuf *p,
+             ip6_addr_t *addr, u16_t port)
+{
+    u8_t msg_header[4];
+    unsigned int msg_type, msg_tid;
+    int copied;
+    size_t roff;
+    struct pbuf *q;
+    err_t error;
+
+    LWIP_UNUSED_ARG(arg);
+    LWIP_ASSERT1(p != NULL);
+
+    copied = pbuf_copy_partial(p, msg_header, sizeof(msg_header), 0);
+    if (copied != sizeof(msg_header)) {
+        DPRINTF(("%s: message header truncated\n", __func__));
+        pbuf_free(p);
+        return;
+    }
+    pbuf_header(p, -(s16_t)sizeof(msg_header));
+
+    msg_type = msg_header[0];
+    msg_tid = (msg_header[1] << 16) | (msg_header[2] << 8) | msg_header[3];
+    DPRINTF(("%s: type %u, tid 0x%6x\n", __func__, msg_type, msg_tid));
+    if (msg_type != DHCP6_INFORMATION_REQUEST) { /** @todo ? RELAY_FORW */
+        pbuf_free(p);
+        return;
+    }
+
+    roff = 0;
+
+    msg_header[0] = DHCP6_REPLY;
+    memcpy(dhcp6ds_reply_buf + roff, msg_header, sizeof(msg_header));
+    roff += sizeof(msg_header);
+
+
+    /* loop over options */
+    while (p->tot_len > 0) {
+        u16_t opt, optlen;
+
+        /* fetch option code */
+        copied = pbuf_copy_partial(p, &opt, sizeof(opt), 0);
+        if (copied != sizeof(opt)) {
+            DPRINTF(("%s: option header truncated\n", __func__));
+            pbuf_free(p);
+            return;
+        }
+        pbuf_header(p, -(s16_t)sizeof(opt));
+        opt = ntohs(opt);
+
+        /* fetch option length */
+        copied = pbuf_copy_partial(p, &optlen, sizeof(optlen), 0);
+        if (copied != sizeof(optlen)) {
+            DPRINTF(("%s: option %u length truncated\n", __func__, opt));
+            pbuf_free(p);
+            return;
+        }
+        pbuf_header(p, -(s16_t)sizeof(optlen));
+        optlen = ntohs(optlen);
+
+        /* enough data? */
+        if (optlen > p->tot_len) {
+            DPRINTF(("%s: option %u truncated: expect %u, got %u\n",
+                     __func__, opt, optlen, p->tot_len));
+            pbuf_free(p);
+            return;
+        }
+
+        DPRINTF2(("%s: option %u length %u\n", __func__, opt, optlen));
+
+        if (opt == DHCP6_OPTION_CLIENTID) {
+            u16_t s;
+
+            /* "A DUID can be no more than 128 octets long (not
+               including the type code)." */
+            if (optlen > 130) {
+                DPRINTF(("%s: client DUID too long: %u\n", __func__, optlen));
+                pbuf_free(p);
+                return;
+            }
+
+            s = PP_HTONS(DHCP6_OPTION_CLIENTID);
+            memcpy(dhcp6ds_reply_buf + roff, &s, sizeof(s));
+            roff += sizeof(s);
+
+            s = ntohs(optlen);
+            memcpy(dhcp6ds_reply_buf + roff, &s, sizeof(s));
+            roff += sizeof(s);
+
+            pbuf_copy_partial(p, dhcp6ds_reply_buf + roff, optlen, 0);
+            roff += optlen;
+        }
+        else if (opt == DHCP6_OPTION_ORO) {
+            u16_t *opts;
+            int i, nopts;
+
+            if (optlen % 2 != 0) {
+                DPRINTF2(("%s: Option Request of odd length\n", __func__));
+                goto bad_oro;
+            }
+            nopts = optlen / 2;
+
+            opts = (u16_t *)malloc(optlen);
+            if (opts == NULL) {
+                DPRINTF2(("%s: failed to allocate space for Option Request\n",
+                          __func__));
+                goto bad_oro;
+            }
+
+            pbuf_copy_partial(p, opts, optlen, 0);
+            for (i = 0; i < nopts; ++i) {
+                opt = ntohs(opts[i]);
+                DPRINTF2(("> request option %u\n", opt));
+            };
+            free(opts);
+
+          bad_oro: /* empty */;
+        }
+
+        pbuf_header(p, -optlen); /* go to next option */
+    }
+    pbuf_free(p);               /* done */
+
+
+    memcpy(dhcp6ds_reply_buf + roff, dhcp6ds_serverid, sizeof(dhcp6ds_serverid));
+    roff += sizeof(dhcp6ds_serverid);
+
+    memcpy(dhcp6ds_reply_buf + roff, dhcp6ds_dns, sizeof(dhcp6ds_dns));
+    roff += sizeof(dhcp6ds_dns);
+
+    Assert(roff == (u16_t)roff);
+    q = pbuf_alloc(PBUF_RAW, (u16_t)roff, PBUF_RAM);
+    if (q == NULL) {
+        DPRINTF(("%s: pbuf_alloc(%d) failed\n", __func__, (int)roff));
+        return;
+    }
+
+    error = pbuf_take(q, dhcp6ds_reply_buf, (u16_t)roff);
+    if (error != ERR_OK) {
+        DPRINTF(("%s: pbuf_take(%d) failed: %s\n",
+                 __func__, (int)roff, proxy_lwip_strerr(error)));
+        pbuf_free(q);
+        return;
+    }
+
+    error = udp_sendto_ip6(pcb, q, addr, port);
+    if (error != ERR_OK) {
+        DPRINTF(("%s: udp_sendto failed: %s\n",
+                 __func__, proxy_lwip_strerr(error)));
+    }
+
+    pbuf_free(q);
+}
diff --git a/src/VBox/NetworkServices/NAT/proxy_pollmgr.c b/src/VBox/NetworkServices/NAT/proxy_pollmgr.c
new file mode 100644
index 00000000..a62c1949
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/proxy_pollmgr.c
@@ -0,0 +1,838 @@
+/* $Id: proxy_pollmgr.c $ */
+/** @file
+ * NAT Network - poll manager.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#define LOG_GROUP LOG_GROUP_NAT_SERVICE
+
+#include "winutils.h"
+
+#include "proxy_pollmgr.h"
+#include "proxy.h"
+
+#ifndef RT_OS_WINDOWS
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <err.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <poll.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+#include <unistd.h>
+#else
+#include <iprt/errcore.h>
+#include <stdlib.h>
+#include <string.h>
+#include "winpoll.h"
+#endif
+
+#include <iprt/req.h>
+#include <iprt/errcore.h>
+
+
+#define POLLMGR_GARBAGE (-1)
+
+
+enum {
+    POLLMGR_QUEUE = 0,
+
+    POLLMGR_SLOT_STATIC_COUNT,
+    POLLMGR_SLOT_FIRST_DYNAMIC = POLLMGR_SLOT_STATIC_COUNT
+};
+
+
+struct pollmgr_chan {
+    struct pollmgr_handler *handler;
+    void *arg;
+    bool arg_valid;
+};
+
+struct pollmgr {
+    struct pollfd *fds;
+    struct pollmgr_handler **handlers;
+    nfds_t capacity;            /* allocated size of the arrays */
+    nfds_t nfds;                /* part of the arrays in use */
+
+    /* channels (socketpair) for static slots */
+    SOCKET chan[POLLMGR_SLOT_STATIC_COUNT][2];
+#define POLLMGR_CHFD_RD 0       /* - pollmgr side */
+#define POLLMGR_CHFD_WR 1       /* - client side */
+
+
+    /* emulate channels with request queue */
+    RTREQQUEUE queue;
+    struct pollmgr_handler queue_handler;
+    struct pollmgr_chan chan_handlers[POLLMGR_CHAN_COUNT];
+} pollmgr;
+
+
+static int pollmgr_queue_callback(struct pollmgr_handler *, SOCKET, int);
+static void pollmgr_chan_call_handler(int, void *);
+
+static void pollmgr_loop(void);
+
+static void pollmgr_add_at(int, struct pollmgr_handler *, SOCKET, int);
+static void pollmgr_refptr_delete(struct pollmgr_refptr *);
+
+
+/*
+ * We cannot portably peek at the length of the incoming datagram and
+ * pre-allocate pbuf chain to recvmsg() directly to it.  On Linux it's
+ * possible to recv with MSG_PEEK|MSG_TRUC, but extra syscall is
+ * probably more expensive (haven't measured) than doing an extra copy
+ * of data, since typical UDP datagrams are small enough to avoid
+ * fragmentation.
+ *
+ * We can use shared buffer here since we read from sockets
+ * sequentially in a loop over pollfd.
+ */
+u8_t pollmgr_udpbuf[64 * 1024];
+
+
+int
+pollmgr_init(void)
+{
+    struct pollfd *newfds;
+    struct pollmgr_handler **newhdls;
+    nfds_t newcap;
+    int rc, status;
+    nfds_t i;
+
+    rc = RTReqQueueCreate(&pollmgr.queue);
+    if (RT_FAILURE(rc))
+        return -1;
+
+    pollmgr.fds = NULL;
+    pollmgr.handlers = NULL;
+    pollmgr.capacity = 0;
+    pollmgr.nfds = 0;
+
+    for (i = 0; i < POLLMGR_SLOT_STATIC_COUNT; ++i) {
+        pollmgr.chan[i][POLLMGR_CHFD_RD] = INVALID_SOCKET;
+        pollmgr.chan[i][POLLMGR_CHFD_WR] = INVALID_SOCKET;
+    }
+
+    for (i = 0; i < POLLMGR_SLOT_STATIC_COUNT; ++i) {
+#ifndef RT_OS_WINDOWS
+        int j;
+
+        status = socketpair(PF_LOCAL, SOCK_DGRAM, 0, pollmgr.chan[i]);
+        if (status < 0) {
+            DPRINTF(("socketpair: %R[sockerr]\n", SOCKERRNO()));
+            goto cleanup_close;
+        }
+
+        /* now manually make them O_NONBLOCK */
+        for (j = 0; j < 2; ++j) {
+            int s = pollmgr.chan[i][j];
+            int sflags;
+
+            sflags = fcntl(s, F_GETFL, 0);
+            if (sflags < 0) {
+                DPRINTF0(("F_GETFL: %R[sockerr]\n", errno));
+                goto cleanup_close;
+            }
+
+            status = fcntl(s, F_SETFL, sflags | O_NONBLOCK);
+            if (status < 0) {
+                DPRINTF0(("O_NONBLOCK: %R[sockerr]\n", errno));
+                goto cleanup_close;
+            }
+        }
+#else
+        status = RTWinSocketPair(PF_INET, SOCK_DGRAM, 0, pollmgr.chan[i]);
+        if (RT_FAILURE(status)) {
+            goto cleanup_close;
+        }
+#endif
+    }
+
+
+    newcap = 16;                /* XXX: magic */
+    LWIP_ASSERT1(newcap >= POLLMGR_SLOT_STATIC_COUNT);
+
+    newfds = (struct pollfd *)
+        malloc(newcap * sizeof(*pollmgr.fds));
+    if (newfds == NULL) {
+        DPRINTF(("%s: Failed to allocate fds array\n", __func__));
+        goto cleanup_close;
+    }
+
+    newhdls = (struct pollmgr_handler **)
+        malloc(newcap * sizeof(*pollmgr.handlers));
+    if (newhdls == NULL) {
+        DPRINTF(("%s: Failed to allocate handlers array\n", __func__));
+        free(newfds);
+        goto cleanup_close;
+    }
+
+    pollmgr.capacity = newcap;
+    pollmgr.fds = newfds;
+    pollmgr.handlers = newhdls;
+
+    pollmgr.nfds = POLLMGR_SLOT_STATIC_COUNT;
+
+    for (i = 0; i < pollmgr.capacity; ++i) {
+        pollmgr.fds[i].fd = INVALID_SOCKET;
+        pollmgr.fds[i].events = 0;
+        pollmgr.fds[i].revents = 0;
+    }
+
+    /* add request queue notification */
+    pollmgr.queue_handler.callback = pollmgr_queue_callback;
+    pollmgr.queue_handler.data = NULL;
+    pollmgr.queue_handler.slot = -1;
+
+    pollmgr_add_at(POLLMGR_QUEUE, &pollmgr.queue_handler,
+                   pollmgr.chan[POLLMGR_QUEUE][POLLMGR_CHFD_RD],
+                   POLLIN);
+
+    return 0;
+
+  cleanup_close:
+    for (i = 0; i < POLLMGR_SLOT_STATIC_COUNT; ++i) {
+        SOCKET *chan = pollmgr.chan[i];
+        if (chan[POLLMGR_CHFD_RD] != INVALID_SOCKET) {
+            closesocket(chan[POLLMGR_CHFD_RD]);
+            closesocket(chan[POLLMGR_CHFD_WR]);
+        }
+    }
+
+    return -1;
+}
+
+
+/*
+ * Add new channel.  We now implement channels with request queue, so
+ * all channels get the same socket that triggers queue processing.
+ *
+ * Must be called before pollmgr loop is started, so no locking.
+ */
+SOCKET
+pollmgr_add_chan(int slot, struct pollmgr_handler *handler)
+{
+    AssertReturn(0 <= slot && slot < POLLMGR_CHAN_COUNT, INVALID_SOCKET);
+    AssertReturn(handler != NULL && handler->callback != NULL, INVALID_SOCKET);
+
+    handler->slot = slot;
+    pollmgr.chan_handlers[slot].handler = handler;
+    return pollmgr.chan[POLLMGR_QUEUE][POLLMGR_CHFD_WR];
+}
+
+
+/*
+ * This used to actually send data over the channel's socket.  Now we
+ * queue a request and send single byte notification over shared
+ * POLLMGR_QUEUE socket.
+ */
+ssize_t
+pollmgr_chan_send(int slot, void *buf, size_t nbytes)
+{
+    static const char notification = 0x5a;
+
+    void *ptr;
+    SOCKET fd;
+    ssize_t nsent;
+    int rc;
+
+    AssertReturn(0 <= slot && slot < POLLMGR_CHAN_COUNT, -1);
+
+    /*
+     * XXX: Hack alert.  We only ever "sent" single pointer which was
+     * simultaneously both the wakeup event for the poll and the
+     * argument for the channel handler that it read from the channel.
+     * So now we pass this pointer to the request and arrange for the
+     * handler to "read" it when it asks for it.
+     */
+    if (nbytes != sizeof(void *)) {
+        return -1;
+    }
+
+    ptr = *(void **)buf;
+
+    rc = RTReqQueueCallEx(pollmgr.queue, NULL, 0,
+                          RTREQFLAGS_VOID | RTREQFLAGS_NO_WAIT,
+                          (PFNRT)pollmgr_chan_call_handler, 2,
+                          slot, ptr);
+
+    fd = pollmgr.chan[POLLMGR_QUEUE][POLLMGR_CHFD_WR];
+    nsent = send(fd, &notification, 1, 0);
+    if (nsent == SOCKET_ERROR) {
+        DPRINTF(("send on chan %d: %R[sockerr]\n", slot, SOCKERRNO()));
+        return -1;
+    }
+    else if ((size_t)nsent != 1) {
+        DPRINTF(("send on chan %d: datagram truncated to %u bytes",
+                 slot, (unsigned int)nsent));
+        return -1;
+    }
+
+    /* caller thinks it's sending the pointer */
+    return sizeof(void *);
+}
+
+
+/*
+ * pollmgr_chan_send() sent us a notification, process the queue.
+ */
+static int
+pollmgr_queue_callback(struct pollmgr_handler *handler, SOCKET fd, int revents)
+{
+    ssize_t nread;
+    int sockerr;
+    int rc;
+
+    RT_NOREF(handler, revents);
+    Assert(pollmgr.queue != NIL_RTREQQUEUE);
+
+    nread = recv(fd, (char *)pollmgr_udpbuf, sizeof(pollmgr_udpbuf), 0);
+    sockerr = SOCKERRNO();      /* save now, may be clobbered */
+
+    if (nread == SOCKET_ERROR) {
+        DPRINTF0(("%s: recv: %R[sockerr]\n", __func__, sockerr));
+        return POLLIN;
+    }
+
+    DPRINTF2(("%s: read %zd\n", __func__, nread));
+    if (nread == 0) {
+        return POLLIN;
+    }
+
+    rc = RTReqQueueProcess(pollmgr.queue, 0);
+    if (RT_UNLIKELY(rc != VERR_TIMEOUT && RT_FAILURE_NP(rc))) {
+        DPRINTF0(("%s: RTReqQueueProcess: %Rrc\n", __func__, rc));
+    }
+
+    return POLLIN;
+}
+
+
+/*
+ * Queued requests use this function to emulate the call to the
+ * handler's callback.
+ */
+static void
+pollmgr_chan_call_handler(int slot, void *arg)
+{
+    struct pollmgr_handler *handler;
+    int nevents;
+
+    AssertReturnVoid(0 <= slot && slot < POLLMGR_CHAN_COUNT);
+
+    handler = pollmgr.chan_handlers[slot].handler;
+    AssertReturnVoid(handler != NULL && handler->callback != NULL);
+
+    /* arrange for pollmgr_chan_recv_ptr() to "receive" the arg */
+    pollmgr.chan_handlers[slot].arg = arg;
+    pollmgr.chan_handlers[slot].arg_valid = true;
+
+    nevents = handler->callback(handler, INVALID_SOCKET, POLLIN);
+    if (nevents != POLLIN) {
+        DPRINTF2(("%s: nevents=0x%x!\n", __func__, nevents));
+    }
+}
+
+
+/*
+ * "Receive" a pointer "sent" over poll manager channel.
+ */
+void *
+pollmgr_chan_recv_ptr(struct pollmgr_handler *handler, SOCKET fd, int revents)
+{
+    int slot;
+    void *ptr;
+
+    RT_NOREF(fd);
+
+    slot = handler->slot;
+    Assert(0 <= slot && slot < POLLMGR_CHAN_COUNT);
+
+    if (revents & POLLNVAL) {
+        errx(EXIT_FAILURE, "chan %d: fd invalid", (int)handler->slot);
+        /* NOTREACHED */
+    }
+
+    if (revents & (POLLERR | POLLHUP)) {
+        errx(EXIT_FAILURE, "chan %d: fd error", (int)handler->slot);
+        /* NOTREACHED */
+    }
+
+    LWIP_ASSERT1(revents & POLLIN);
+
+    if (!pollmgr.chan_handlers[slot].arg_valid) {
+        err(EXIT_FAILURE, "chan %d: recv", (int)handler->slot);
+        /* NOTREACHED */
+    }
+
+    ptr = pollmgr.chan_handlers[slot].arg;
+    pollmgr.chan_handlers[slot].arg_valid = false;
+
+    return ptr;
+}
+
+
+/*
+ * Must be called from pollmgr loop (via callbacks), so no locking.
+ */
+int
+pollmgr_add(struct pollmgr_handler *handler, SOCKET fd, int events)
+{
+    int slot;
+
+    DPRINTF2(("%s: new fd %d\n", __func__, fd));
+
+    if (pollmgr.nfds == pollmgr.capacity) {
+        struct pollfd *newfds;
+        struct pollmgr_handler **newhdls;
+        nfds_t newcap;
+        nfds_t i;
+
+        newcap = pollmgr.capacity * 2;
+
+        newfds = (struct pollfd *)
+            realloc(pollmgr.fds, newcap * sizeof(*pollmgr.fds));
+        if (newfds == NULL) {
+            DPRINTF(("%s: Failed to reallocate fds array\n", __func__));
+            handler->slot = -1;
+            return -1;
+        }
+
+        pollmgr.fds = newfds; /* don't crash/leak if realloc(handlers) fails */
+        /* but don't update capacity yet! */
+
+        newhdls = (struct pollmgr_handler **)
+            realloc(pollmgr.handlers, newcap * sizeof(*pollmgr.handlers));
+        if (newhdls == NULL) {
+            DPRINTF(("%s: Failed to reallocate handlers array\n", __func__));
+            /* if we failed to realloc here, then fds points to the
+             * new array, but we pretend we still has old capacity */
+            handler->slot = -1;
+            return -1;
+        }
+
+        pollmgr.handlers = newhdls;
+        pollmgr.capacity = newcap;
+
+        for (i = pollmgr.nfds; i < newcap; ++i) {
+            newfds[i].fd = INVALID_SOCKET;
+            newfds[i].events = 0;
+            newfds[i].revents = 0;
+            newhdls[i] = NULL;
+        }
+    }
+
+    slot = pollmgr.nfds;
+    ++pollmgr.nfds;
+
+    pollmgr_add_at(slot, handler, fd, events);
+    return slot;
+}
+
+
+static void
+pollmgr_add_at(int slot, struct pollmgr_handler *handler, SOCKET fd, int events)
+{
+    pollmgr.fds[slot].fd = fd;
+    pollmgr.fds[slot].events = events;
+    pollmgr.fds[slot].revents = 0;
+    pollmgr.handlers[slot] = handler;
+
+    handler->slot = slot;
+}
+
+
+void
+pollmgr_update_events(int slot, int events)
+{
+    LWIP_ASSERT1(slot >= POLLMGR_SLOT_FIRST_DYNAMIC);
+    LWIP_ASSERT1((nfds_t)slot < pollmgr.nfds);
+
+    pollmgr.fds[slot].events = events;
+}
+
+
+void
+pollmgr_del_slot(int slot)
+{
+    LWIP_ASSERT1(slot >= POLLMGR_SLOT_FIRST_DYNAMIC);
+
+    DPRINTF2(("%s(%d): fd %d ! DELETED\n",
+              __func__, slot, pollmgr.fds[slot].fd));
+
+    pollmgr.fds[slot].fd = INVALID_SOCKET; /* see poll loop */
+}
+
+
+void
+pollmgr_thread(void *ignored)
+{
+    LWIP_UNUSED_ARG(ignored);
+    pollmgr_loop();
+}
+
+
+static void
+pollmgr_loop(void)
+{
+    int nready;
+    SOCKET delfirst;
+    SOCKET *pdelprev;
+    int i;
+
+    for (;;) {
+#ifndef RT_OS_WINDOWS
+        nready = poll(pollmgr.fds, pollmgr.nfds, -1);
+#else
+        int rc = RTWinPoll(pollmgr.fds, pollmgr.nfds,RT_INDEFINITE_WAIT, &nready);
+        if (RT_FAILURE(rc)) {
+            err(EXIT_FAILURE, "poll"); /* XXX: what to do on error? */
+            /* NOTREACHED*/
+        }
+#endif
+
+        DPRINTF2(("%s: ready %d fd%s\n",
+                  __func__, nready, (nready == 1 ? "" : "s")));
+
+        if (nready < 0) {
+            if (errno == EINTR) {
+                continue;
+            }
+
+            err(EXIT_FAILURE, "poll"); /* XXX: what to do on error? */
+            /* NOTREACHED*/
+        }
+        else if (nready == 0) { /* cannot happen, we wait forever (-1) */
+            continue;           /* - but be defensive */
+        }
+
+
+        delfirst = INVALID_SOCKET;
+        pdelprev = &delfirst;
+
+        for (i = 0; (nfds_t)i < pollmgr.nfds && nready > 0; ++i) {
+            struct pollmgr_handler *handler;
+            SOCKET fd;
+            int revents, nevents;
+
+            fd = pollmgr.fds[i].fd;
+            revents = pollmgr.fds[i].revents;
+
+            /*
+             * Channel handlers can request deletion of dynamic slots
+             * by calling pollmgr_del_slot() that clobbers slot's fd.
+             */
+            if (fd == INVALID_SOCKET && i >= POLLMGR_SLOT_FIRST_DYNAMIC) {
+                /* adjust count if events were pending for that slot */
+                if (revents != 0) {
+                    --nready;
+                }
+
+                /* pretend that slot handler requested deletion */
+                nevents = -1;
+                goto update_events;
+            }
+
+            if (revents == 0) {
+                continue; /* next fd */
+            }
+            --nready;
+
+            handler = pollmgr.handlers[i];
+
+            if (handler != NULL && handler->callback != NULL) {
+#ifdef LWIP_PROXY_DEBUG
+# if LWIP_PROXY_DEBUG /* DEBUG */
+                if (i < POLLMGR_SLOT_FIRST_DYNAMIC) {
+                    if (revents == POLLIN) {
+                        DPRINTF2(("%s: ch %d\n", __func__, i));
+                    }
+                    else {
+                        DPRINTF2(("%s: ch %d @ revents 0x%x!\n",
+                                  __func__, i, revents));
+                    }
+                }
+                else {
+                    DPRINTF2(("%s: fd %d @ revents 0x%x\n",
+                              __func__, fd, revents));
+                }
+# endif /* LWIP_PROXY_DEBUG / DEBUG */
+#endif
+                nevents = (*handler->callback)(handler, fd, revents);
+            }
+            else {
+                DPRINTF0(("%s: invalid handler for fd %d: ", __func__, fd));
+                if (handler == NULL) {
+                    DPRINTF0(("NULL\n"));
+                }
+                else {
+                    DPRINTF0(("%p (callback = NULL)\n", (void *)handler));
+                }
+                nevents = -1;   /* delete it */
+            }
+
+          update_events:
+            if (nevents >= 0) {
+                if (nevents != pollmgr.fds[i].events) {
+                    DPRINTF2(("%s: fd %d ! nevents 0x%x\n",
+                              __func__, fd, nevents));
+                }
+                pollmgr.fds[i].events = nevents;
+            }
+            else if (i < POLLMGR_SLOT_FIRST_DYNAMIC) {
+                /* Don't garbage-collect channels. */
+                DPRINTF2(("%s: fd %d ! DELETED (channel %d)\n",
+                          __func__, fd, i));
+                pollmgr.fds[i].fd = INVALID_SOCKET;
+                pollmgr.fds[i].events = 0;
+                pollmgr.fds[i].revents = 0;
+                pollmgr.handlers[i] = NULL;
+            }
+            else {
+                DPRINTF2(("%s: fd %d ! DELETED\n", __func__, fd));
+
+                /* schedule for deletion (see g/c loop for details) */
+                *pdelprev = i;  /* make previous entry point to us */
+                pdelprev = &pollmgr.fds[i].fd;
+
+                pollmgr.fds[i].fd = INVALID_SOCKET; /* end of list (for now) */
+                pollmgr.fds[i].events = POLLMGR_GARBAGE;
+                pollmgr.fds[i].revents = 0;
+                pollmgr.handlers[i] = NULL;
+            }
+        } /* processing loop */
+
+
+        /*
+         * Garbage collect and compact the array.
+         *
+         * We overload pollfd::fd of garbage entries to store the
+         * index of the next garbage entry.  The garbage list is
+         * co-directional with the fds array.  The index of the first
+         * entry is in "delfirst", the last entry "points to"
+         * INVALID_SOCKET.
+         *
+         * See update_events code for nevents < 0 at the end of the
+         * processing loop above.
+         */
+        while (delfirst != INVALID_SOCKET) {
+            const int last = pollmgr.nfds - 1;
+
+            /*
+             * We want a live entry in the last slot to swap into the
+             * freed slot, so make sure we have one.
+             */
+            if (pollmgr.fds[last].events == POLLMGR_GARBAGE /* garbage */
+                || pollmgr.fds[last].fd == INVALID_SOCKET)  /* or killed */
+            {
+                /* drop garbage entry at the end of the array */
+                --pollmgr.nfds;
+
+                if (delfirst == (SOCKET)last) {
+                    /* congruent to delnext >= pollmgr.nfds test below */
+                    delfirst = INVALID_SOCKET; /* done */
+                }
+            }
+            else {
+                const SOCKET delnext = pollmgr.fds[delfirst].fd;
+
+                /* copy live entry at the end to the first slot being freed */
+                pollmgr.fds[delfirst] = pollmgr.fds[last]; /* struct copy */
+                pollmgr.handlers[delfirst] = pollmgr.handlers[last];
+                pollmgr.handlers[delfirst]->slot = (int)delfirst;
+                --pollmgr.nfds;
+
+                if ((nfds_t)delnext >= pollmgr.nfds) {
+                    delfirst = INVALID_SOCKET; /* done */
+                }
+                else {
+                    delfirst = delnext;
+                }
+            }
+
+            pollmgr.fds[last].fd = INVALID_SOCKET;
+            pollmgr.fds[last].events = 0;
+            pollmgr.fds[last].revents = 0;
+            pollmgr.handlers[last] = NULL;
+        }
+    } /* poll loop */
+}
+
+
+/**
+ * Create strongly held refptr.
+ */
+struct pollmgr_refptr *
+pollmgr_refptr_create(struct pollmgr_handler *ptr)
+{
+    struct pollmgr_refptr *rp;
+
+    LWIP_ASSERT1(ptr != NULL);
+
+    rp = (struct pollmgr_refptr *)malloc(sizeof (*rp));
+    if (rp == NULL) {
+        return NULL;
+    }
+
+    sys_mutex_new(&rp->lock);
+    rp->ptr = ptr;
+    rp->strong = 1;
+    rp->weak = 0;
+
+    return rp;
+}
+
+
+static void
+pollmgr_refptr_delete(struct pollmgr_refptr *rp)
+{
+    if (rp == NULL) {
+        return;
+    }
+
+    LWIP_ASSERT1(rp->strong == 0);
+    LWIP_ASSERT1(rp->weak == 0);
+
+    sys_mutex_free(&rp->lock);
+    free(rp);
+}
+
+
+/**
+ * Add weak reference before "rp" is sent over a poll manager channel.
+ */
+void
+pollmgr_refptr_weak_ref(struct pollmgr_refptr *rp)
+{
+    sys_mutex_lock(&rp->lock);
+
+    LWIP_ASSERT1(rp->ptr != NULL);
+    LWIP_ASSERT1(rp->strong > 0);
+
+    ++rp->weak;
+
+    sys_mutex_unlock(&rp->lock);
+}
+
+
+/**
+ * Try to get the pointer from implicitely weak reference we've got
+ * from a channel.
+ *
+ * If we detect that the object is still strongly referenced, but no
+ * longer registered with the poll manager we abort strengthening
+ * conversion here b/c lwip thread callback is already scheduled to
+ * destruct the object.
+ */
+struct pollmgr_handler *
+pollmgr_refptr_get(struct pollmgr_refptr *rp)
+{
+    struct pollmgr_handler *handler;
+    size_t weak;
+
+    sys_mutex_lock(&rp->lock);
+
+    LWIP_ASSERT1(rp->weak > 0);
+    weak = --rp->weak;
+
+    handler = rp->ptr;
+    if (handler == NULL) {
+        LWIP_ASSERT1(rp->strong == 0);
+        sys_mutex_unlock(&rp->lock);
+        if (weak == 0) {
+            pollmgr_refptr_delete(rp);
+        }
+        return NULL;
+    }
+
+    LWIP_ASSERT1(rp->strong == 1);
+
+    /*
+     * Here we woild do:
+     *
+     *   ++rp->strong;
+     *
+     * and then, after channel handler is done, we would decrement it
+     * back.
+     *
+     * Instead we check that the object is still registered with poll
+     * manager. If it is, there's no race with lwip thread trying to
+     * drop its strong reference, as lwip thread callback to destruct
+     * the object is always scheduled by its poll manager callback.
+     *
+     * Conversly, if we detect that the object is no longer registered
+     * with poll manager, we immediately abort. Since channel handler
+     * can't do anything useful anyway and would have to return
+     * immediately.
+     *
+     * Since channel handler would always find rp->strong as it had
+     * left it, just elide extra strong reference creation to avoid
+     * the whole back-and-forth.
+     */
+
+    if (handler->slot < 0) { /* no longer polling */
+        sys_mutex_unlock(&rp->lock);
+        return NULL;
+    }
+
+    sys_mutex_unlock(&rp->lock);
+    return handler;
+}
+
+
+/**
+ * Remove (the only) strong reference.
+ *
+ * If it were real strong/weak pointers, we should also call
+ * destructor for the referenced object, but
+ */
+void
+pollmgr_refptr_unref(struct pollmgr_refptr *rp)
+{
+    sys_mutex_lock(&rp->lock);
+
+    LWIP_ASSERT1(rp->strong == 1);
+    --rp->strong;
+
+    if (rp->strong > 0) {
+        sys_mutex_unlock(&rp->lock);
+    }
+    else {
+        size_t weak;
+
+        /* void *ptr = rp->ptr; */
+        rp->ptr = NULL;
+
+        /* delete ptr; // see doc comment */
+
+        weak = rp->weak;
+        sys_mutex_unlock(&rp->lock);
+        if (weak == 0) {
+            pollmgr_refptr_delete(rp);
+        }
+    }
+}
diff --git a/src/VBox/NetworkServices/NAT/proxy_pollmgr.h b/src/VBox/NetworkServices/NAT/proxy_pollmgr.h
new file mode 100644
index 00000000..9ab6bf19
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/proxy_pollmgr.h
@@ -0,0 +1,95 @@
+/* $Id: proxy_pollmgr.h $ */
+/** @file
+ * NAT Network - poll manager, definitions and declarations.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#ifndef VBOX_INCLUDED_SRC_NAT_proxy_pollmgr_h
+#define VBOX_INCLUDED_SRC_NAT_proxy_pollmgr_h
+#ifndef RT_WITHOUT_PRAGMA_ONCE
+# pragma once
+#endif
+
+#ifndef RT_OS_WINDOWS
+# include <unistd.h>             /* for ssize_t */
+#endif
+#include "lwip/sys.h"
+
+enum pollmgr_slot_t {
+    POLLMGR_CHAN_PXTCP_ADD,     /* new proxy tcp connection from guest */
+    POLLMGR_CHAN_PXTCP_POLLIN,  /* free space in ringbuf, may POLLIN */
+    POLLMGR_CHAN_PXTCP_POLLOUT, /* schedule one-shot POLLOUT callback */
+    POLLMGR_CHAN_PXTCP_DEL,     /* delete pxtcp */
+    POLLMGR_CHAN_PXTCP_RESET,   /* send RST and delete pxtcp */
+
+    POLLMGR_CHAN_PXUDP_ADD,     /* new proxy udp conversation from guest */
+    POLLMGR_CHAN_PXUDP_DEL,     /* delete pxudp from pollmgr */
+
+    POLLMGR_CHAN_PORTFWD,       /* add/remove port forwarding rules */
+
+    POLLMGR_CHAN_COUNT
+};
+
+
+struct pollmgr_handler;         /* forward */
+typedef int (*pollmgr_callback)(struct pollmgr_handler *, SOCKET, int);
+
+struct pollmgr_handler {
+    pollmgr_callback callback;
+    void *data;
+    int slot;
+};
+
+struct pollmgr_refptr {
+    struct pollmgr_handler *ptr;
+    sys_mutex_t lock;
+    size_t strong;
+    size_t weak;
+};
+
+int pollmgr_init(void);
+
+/* static named slots (aka "channels") */
+SOCKET pollmgr_add_chan(int, struct pollmgr_handler *);
+ssize_t pollmgr_chan_send(int, void *buf, size_t nbytes);
+void *pollmgr_chan_recv_ptr(struct pollmgr_handler *, SOCKET, int);
+
+/* dynamic slots */
+int pollmgr_add(struct pollmgr_handler *, SOCKET, int);
+
+/* special-purpose strong/weak references */
+struct pollmgr_refptr *pollmgr_refptr_create(struct pollmgr_handler *);
+void pollmgr_refptr_weak_ref(struct pollmgr_refptr *);
+struct pollmgr_handler *pollmgr_refptr_get(struct pollmgr_refptr *);
+void pollmgr_refptr_unref(struct pollmgr_refptr *);
+
+void pollmgr_update_events(int, int);
+void pollmgr_del_slot(int);
+
+void pollmgr_thread(void *);
+
+/* buffer for callbacks to receive udp without worrying about truncation */
+extern u8_t pollmgr_udpbuf[64 * 1024];
+
+#endif /* !VBOX_INCLUDED_SRC_NAT_proxy_pollmgr_h */
diff --git a/src/VBox/NetworkServices/NAT/proxy_rtadvd.c b/src/VBox/NetworkServices/NAT/proxy_rtadvd.c
new file mode 100644
index 00000000..8ba2d3fc
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/proxy_rtadvd.c
@@ -0,0 +1,427 @@
+/* $Id: proxy_rtadvd.c $ */
+/** @file
+ * NAT Network - IPv6 router advertisement daemon.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#define LOG_GROUP LOG_GROUP_NAT_SERVICE
+
+#include "winutils.h"
+
+#include "proxy.h"
+
+#include "lwip/opt.h"
+#include "lwip/sys.h"
+#include "lwip/stats.h"
+#include "lwip/timers.h"
+
+#include "lwip/inet_chksum.h"
+#include "lwip/icmp6.h"
+#include "lwip/nd6.h"
+
+#include "lwip/raw.h"
+
+#include <string.h>
+
+
+static void proxy_rtadvd_timer(void *);
+static void proxy_rtadvd_send_multicast(struct netif *);
+static void proxy_rtadvd_fill_payload(struct netif *, int);
+
+static u8_t rtadvd_recv(void *, struct raw_pcb *, struct pbuf *, ip6_addr_t *);
+
+
+/* ff02::1 - link-local all nodes multicast address */
+static ip6_addr_t allnodes_linklocal = {
+    { PP_HTONL(0xff020000UL), 0, 0, PP_HTONL(0x00000001UL) }
+};
+
+
+/*
+ * Unsolicited Router Advertisement payload.
+ *
+ * NB: Since ICMP checksum covers pseudo-header with destination
+ * address (link-local allnodes multicast in this case) this payload
+ * cannot be used for solicited replies to unicast addresses.
+ */
+static unsigned int unsolicited_ra_payload_length;
+static u8_t unsolicited_ra_payload[
+      sizeof(struct ra_header)
+      /* reserves enough space for NETIF_MAX_HWADDR_LEN */
+    + sizeof(struct lladdr_option)
+      /* we only announce one prefix */
+    + sizeof(struct prefix_option) * 1
+];
+
+
+static int ndefaults = 0;
+
+static struct raw_pcb *rtadvd_pcb;
+
+
+void
+proxy_rtadvd_start(struct netif *proxy_netif)
+{
+#if 0 /* XXX */
+    ndefaults = rtmon_get_defaults();
+#else
+    ndefaults = g_proxy_options->ipv6_defroute;
+#endif
+    if (ndefaults < 0) {
+        DPRINTF0(("rtadvd: failed to read IPv6 routing table, aborting\n"));
+        return;
+    }
+
+    proxy_rtadvd_fill_payload(proxy_netif, ndefaults > 0);
+
+    rtadvd_pcb = raw_new_ip6(IP6_NEXTH_ICMP6);
+    if (rtadvd_pcb == NULL) {
+        DPRINTF0(("rtadvd: failed to allocate pcb, aborting\n"));
+        return;
+    }
+
+    /*
+     * We cannot use raw_bind_ip6() since raw_input() doesn't grok
+     * multicasts.  We are going to use ip6_output_if() directly.
+     */
+    raw_recv_ip6(rtadvd_pcb, rtadvd_recv, proxy_netif);
+
+    sys_timeout(3 * 1000, proxy_rtadvd_timer, proxy_netif);
+}
+
+
+static int quick_ras = 2;
+
+
+/**
+ * lwIP thread callback invoked when we start/stop advertising default
+ * route.
+ */
+void
+proxy_rtadvd_do_quick(void *arg)
+{
+    struct netif *proxy_netif = (struct netif *)arg;
+
+    quick_ras = 2;
+    sys_untimeout(proxy_rtadvd_timer, proxy_netif);
+    proxy_rtadvd_timer(proxy_netif); /* sends and re-arms */
+}
+
+
+static void
+proxy_rtadvd_timer(void *arg)
+{
+    struct netif *proxy_netif = (struct netif *)arg;
+    int newdefs;
+    u32_t delay;
+
+#if 0 /* XXX */
+    newdefs = rtmon_get_defaults();
+#else
+    newdefs = g_proxy_options->ipv6_defroute;
+#endif
+    if (newdefs != ndefaults && newdefs != -1) {
+        ndefaults = newdefs;
+        proxy_rtadvd_fill_payload(proxy_netif, ndefaults > 0);
+    }
+
+    proxy_rtadvd_send_multicast(proxy_netif);
+
+    if (quick_ras > 0) {
+        --quick_ras;
+        delay = 16 * 1000;
+    }
+    else {
+        delay = 600 * 1000;
+    }
+
+    sys_timeout(delay, proxy_rtadvd_timer, proxy_netif);
+}
+
+
+/*
+ * This should be folded into icmp6/nd6 input, but I don't want to
+ * solve this in general, making it configurable, etc.
+ *
+ * Cf. RFC 4861:
+ *   6.1.1. Validation of Router Solicitation Messages
+ */
+static u8_t
+rtadvd_recv(void *arg, struct raw_pcb *pcb, struct pbuf *p, ip6_addr_t *addr)
+{
+    enum raw_recv_status { RAW_RECV_CONTINUE = 0, RAW_RECV_CONSUMED = 1 };
+
+    struct netif *proxy_netif = (struct netif *)arg;
+    struct ip6_hdr *ip6_hdr;
+    struct icmp6_hdr *icmp6_hdr;
+    struct lladdr_option *lladdr_opt;
+    void *option;
+    u8_t opttype, optlen8;
+
+    LWIP_UNUSED_ARG(pcb);
+    LWIP_UNUSED_ARG(addr);
+
+    /* save a pointer to IP6 header and skip to ICMP6 payload */
+    ip6_hdr = (struct ip6_hdr *)p->payload;
+    pbuf_header(p, -ip_current_header_tot_len());
+
+    if (p->len < sizeof(struct icmp6_hdr)) {
+        ICMP6_STATS_INC(icmp6.lenerr);
+        goto drop;
+    }
+
+    if (ip6_chksum_pseudo(p, IP6_NEXTH_ICMP6, p->tot_len,
+                          ip6_current_src_addr(),
+                          ip6_current_dest_addr()) != 0)
+    {
+        ICMP6_STATS_INC(icmp6.chkerr);
+        goto drop;
+    }
+
+    icmp6_hdr = (struct icmp6_hdr *)p->payload;
+    if (icmp6_hdr->type != ICMP6_TYPE_RS) {
+        pbuf_header(p, ip_current_header_tot_len()); /* restore payload ptr */
+        return RAW_RECV_CONTINUE; /* not interested */
+    }
+
+    /* only now that we know it's ICMP6_TYPE_RS we can check IP6 hop limit */
+    if (IP6H_HOPLIM(ip6_hdr) != 255) {
+        ICMP6_STATS_INC(icmp6.proterr);
+        goto drop;
+    }
+
+    /* future, backward-incompatible changes may use different Code values. */
+    if (icmp6_hdr->code != 0) {
+        ICMP6_STATS_INC(icmp6.proterr);
+        goto drop;
+    }
+
+    /* skip past rs_header, nothing interesting in it */
+    if (p->len < sizeof(struct rs_header)) {
+        ICMP6_STATS_INC(icmp6.lenerr);
+        goto drop;
+    }
+    pbuf_header(p, -(s16_t)sizeof(struct rs_header));
+
+    lladdr_opt = NULL;
+    while (p->len > 0) {
+        int optlen;
+
+        if (p->len < 8) {
+            ICMP6_STATS_INC(icmp6.lenerr);
+            goto drop;
+        }
+
+        option = p->payload;
+        opttype = ((u8_t *)option)[0];
+        optlen8 = ((u8_t *)option)[1]; /* in units of 8 octets */
+
+        if (optlen8 == 0) {
+            ICMP6_STATS_INC(icmp6.proterr);
+            goto drop;
+        }
+
+        optlen = (unsigned int)optlen8 << 3;
+        if (p->len < optlen) {
+            ICMP6_STATS_INC(icmp6.lenerr);
+            goto drop;
+        }
+
+        if (opttype == ND6_OPTION_TYPE_SOURCE_LLADDR) {
+            if (lladdr_opt != NULL) { /* duplicate */
+                ICMP6_STATS_INC(icmp6.proterr);
+                goto drop;
+            }
+            lladdr_opt = (struct lladdr_option *)option;
+        }
+
+        pbuf_header(p, -optlen);
+    }
+
+    if (ip6_addr_isany(ip6_current_src_addr())) {
+        if (lladdr_opt != NULL) {
+            ICMP6_STATS_INC(icmp6.proterr);
+            goto drop;
+        }
+
+        /* reply with multicast RA */
+    }
+    else {
+        /*
+         * XXX: Router is supposed to update its Neighbor Cache (6.2.6),
+         * but it's hidden inside nd6.c.
+         */
+
+        /* may reply with either unicast or multicast RA */
+    }
+    /* we just always reply with multicast RA */
+
+    pbuf_free(p);               /* NB: this invalidates lladdr_option */
+
+    sys_untimeout(proxy_rtadvd_timer, proxy_netif);
+    proxy_rtadvd_timer(proxy_netif); /* sends and re-arms */
+
+    return RAW_RECV_CONSUMED;
+
+  drop:
+    pbuf_free(p);
+    ICMP6_STATS_INC(icmp6.drop);
+    return RAW_RECV_CONSUMED;
+}
+
+
+static void
+proxy_rtadvd_send_multicast(struct netif *proxy_netif)
+{
+    struct pbuf *ph, *pp;
+    err_t error;
+
+    ph = pbuf_alloc(PBUF_IP, 0, PBUF_RAM);
+    if (ph == NULL) {
+        DPRINTF0(("%s: failed to allocate RA header pbuf\n", __func__));
+        return;
+    }
+
+    pp = pbuf_alloc(PBUF_RAW, unsolicited_ra_payload_length, PBUF_ROM);
+    if (pp == NULL) {
+        DPRINTF0(("%s: failed to allocate RA payload pbuf\n", __func__));
+        pbuf_free(ph);
+        return;
+    }
+    pp->payload = unsolicited_ra_payload;
+    pbuf_chain(ph, pp);
+
+    error = ip6_output_if(ph,
+                          netif_ip6_addr(proxy_netif, 0), /* src: link-local */
+                          &allnodes_linklocal,            /* dst */
+                          255,                            /* hop limit */
+                          0,                              /* traffic class */
+                          IP6_NEXTH_ICMP6,
+                          proxy_netif);
+    if (error != ERR_OK) {
+        DPRINTF0(("%s: failed to send RA (err=%d)\n", __func__, error));
+    }
+
+    pbuf_free(pp);
+    pbuf_free(ph);
+}
+
+
+/*
+ * XXX: TODO: Only ra_header::router_lifetime (and hence
+ * ra_header::chksum) need to be changed, so we can precompute it once
+ * and then only update these two fields.
+ */
+static void
+proxy_rtadvd_fill_payload(struct netif *proxy_netif, int is_default)
+{
+    struct pbuf *p;
+    struct ra_header *ra_hdr;
+    struct lladdr_option *lladdr_opt;
+    struct prefix_option *pfx_opt;
+    unsigned int lladdr_optlen;
+
+    LWIP_ASSERT("netif hwaddr too long",
+                proxy_netif->hwaddr_len <= NETIF_MAX_HWADDR_LEN);
+
+    /* type + length + ll addr + round up to 8 octets */
+    lladdr_optlen = (2 + proxy_netif->hwaddr_len + 7) & ~0x7;
+
+    /* actual payload length */
+    unsolicited_ra_payload_length =
+          sizeof(struct ra_header)
+        + lladdr_optlen
+        + sizeof(struct prefix_option) * 1;
+
+    /* Set fields. */
+    ra_hdr = (struct ra_header *)unsolicited_ra_payload;
+    lladdr_opt = (struct lladdr_option *)((u8_t *)ra_hdr + sizeof(struct ra_header));
+    pfx_opt = (struct prefix_option *)((u8_t *)lladdr_opt + lladdr_optlen);
+
+    memset(unsolicited_ra_payload, 0, sizeof(unsolicited_ra_payload));
+
+    ra_hdr->type = ICMP6_TYPE_RA;
+
+#if 0
+    /*
+     * "M" flag.  Tell guests to use stateful DHCP6.  Disabled here
+     * since we don't provide stateful server.
+     */
+    ra_hdr->flags |= ND6_RA_FLAG_MANAGED_ADDR_CONFIG;
+#endif
+    /*
+     * XXX: TODO: Disable "O" flag for now to match disabled stateless
+     * server.  We don't yet get IPv6 nameserver addresses from
+     * HostDnsService, so we have nothing to say, don't tell guests to
+     * come asking.
+     */
+#if 0
+    /*
+     * "O" flag.  Tell guests to use DHCP6 for DNS and the like.  This
+     * is served by simple stateless server (RFC 3736).
+     *
+     * XXX: "STATEFUL" in the flag name was probably a bug in RFC2461.
+     * It's present in the text, but not in the router configuration
+     * variable name.  It's dropped in the text in RFC4861.
+     */
+    ra_hdr->flags |= ND6_RA_FLAG_OTHER_STATEFUL_CONFIG;
+#endif
+
+    if (is_default) {
+        ra_hdr->router_lifetime = PP_HTONS(1200); /* seconds */
+    }
+    else {
+        ra_hdr->router_lifetime = 0;
+    }
+
+    lladdr_opt->type = ND6_OPTION_TYPE_SOURCE_LLADDR;
+    lladdr_opt->length = lladdr_optlen >> 3; /* in units of 8 octets */
+    memcpy(lladdr_opt->addr, proxy_netif->hwaddr, proxy_netif->hwaddr_len);
+
+    pfx_opt->type = ND6_OPTION_TYPE_PREFIX_INFO;
+    pfx_opt->length = 4;
+    pfx_opt->prefix_length = 64;
+    pfx_opt->flags = ND6_PREFIX_FLAG_ON_LINK
+        | ND6_PREFIX_FLAG_AUTONOMOUS;
+    pfx_opt->valid_lifetime = ~0U; /* infinite */
+    pfx_opt->preferred_lifetime = ~0U; /* infinite */
+    pfx_opt->prefix.addr[0] = netif_ip6_addr(proxy_netif, 1)->addr[0];
+    pfx_opt->prefix.addr[1] = netif_ip6_addr(proxy_netif, 1)->addr[1];
+
+
+    /* we need a temp pbuf to calculate the checksum */
+    p = pbuf_alloc(PBUF_IP, unsolicited_ra_payload_length, PBUF_ROM);
+    if (p == NULL) {
+        DPRINTF0(("rtadvd: failed to allocate RA pbuf\n"));
+        return;
+    }
+    p->payload = unsolicited_ra_payload;
+
+    ra_hdr->chksum = ip6_chksum_pseudo(p, IP6_NEXTH_ICMP6, p->len,
+                                       /* src addr: netif's link-local */
+                                       netif_ip6_addr(proxy_netif, 0),
+                                       /* dst addr */
+                                       &allnodes_linklocal);
+    pbuf_free(p);
+}
diff --git a/src/VBox/NetworkServices/NAT/proxy_tftpd.c b/src/VBox/NetworkServices/NAT/proxy_tftpd.c
new file mode 100644
index 00000000..6baa2cae
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/proxy_tftpd.c
@@ -0,0 +1,991 @@
+/* $Id: proxy_tftpd.c $ */
+/** @file
+ * NAT Network - TFTP server.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#define LOG_GROUP LOG_GROUP_NAT_SERVICE
+
+#include "winutils.h"
+
+#include "proxy.h"
+#include "tftp.h"
+
+#ifndef RT_OS_WINDOWS
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#else
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <io.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <string.h>
+
+# define O_RDONLY _O_RDONLY
+# define S_ISREG(x) ((x) & _S_IFREG)
+#endif
+
+#include "lwip/timers.h"
+#include "lwip/udp.h"
+
+#include <iprt/string.h>
+
+struct xfer {
+    struct udp_pcb *pcb;
+    int fd;
+    unsigned int ack;
+    struct pbuf *pbuf;
+
+    struct pbuf *oack;
+
+    int rexmit;
+
+    ipX_addr_t peer_ip;
+    u16_t peer_port;
+
+    char *filename;
+    int octet;
+
+    /* options */
+    unsigned int blksize;
+    int blksize_from_opt;
+
+    unsigned int timeout;
+    int timeout_from_opt;
+
+    off_t tsize;
+    int tsize_from_opt;
+};
+
+struct tftpd {
+    struct udp_pcb *pcb;
+    char *root;
+
+#define TFTP_MAX_XFERS 3
+    struct xfer xfers[TFTP_MAX_XFERS];
+};
+
+struct tftp_option {
+    const char *name;
+    int (*getopt)(struct xfer *, const char *);
+    int (*ackopt)(struct xfer *, char **, size_t *);
+};
+
+
+static void tftpd_recv(void *, struct udp_pcb *, struct pbuf *, ip_addr_t *, u16_t);
+
+static void tftpd_rrq(struct pbuf *, ip_addr_t *, u16_t);
+
+static void tftp_xfer_recv(void *, struct udp_pcb *, struct pbuf *, ip_addr_t *, u16_t);
+
+static void tftp_recv_ack(struct xfer *, u16_t);
+static void tftp_fillbuf(struct xfer *);
+static void tftp_send(struct xfer *);
+static void tftp_timeout(void *);
+
+static struct xfer *tftp_xfer_alloc(ip_addr_t *, u16_t);
+static int tftp_xfer_create_pcb(struct xfer *);
+static void tftp_xfer_free(struct xfer *);
+
+static int tftp_parse_filename(struct xfer *, char **, size_t *);
+static int tftp_parse_mode(struct xfer *, char **, size_t *);
+static int tftp_parse_option(struct xfer *, char **, size_t *);
+
+static int tftp_opt_blksize(struct xfer *, const char *);
+static int tftp_opt_timeout(struct xfer *, const char *);
+static int tftp_opt_tsize(struct xfer *, const char *);
+
+static char *tftp_getstr(struct xfer *, const char *, char **, size_t *);
+
+static int tftp_ack_blksize(struct xfer *, char **, size_t *);
+static int tftp_ack_timeout(struct xfer *, char **, size_t *);
+static int tftp_ack_tsize(struct xfer *, char **, size_t *);
+
+static int tftp_add_oack(char **, size_t *, const char *, const char *, ...) __attribute__((format(printf, 4, 5)));
+
+static ssize_t tftp_strnlen(char *, size_t);
+
+static int tftp_internal_error(struct xfer *);
+static int tftp_error(struct xfer *, u16_t, const char *, ...) __attribute__((format(printf, 3, 4)));
+static void tftpd_error(ip_addr_t *, u16_t, u16_t, const char *, ...) __attribute__((format(printf, 4, 5)));
+static struct pbuf *tftp_verror(u16_t, const char *, va_list);
+
+
+/* const */ int report_transient_errors = 1;
+static struct tftpd tftpd;
+
+static struct tftp_option tftp_options[] = {
+    { "blksize", tftp_opt_blksize, tftp_ack_blksize }, /* RFC 2348  */
+    { "timeout", tftp_opt_timeout, tftp_ack_timeout }, /* RFC 2349 */
+    { "tsize",   tftp_opt_tsize,   tftp_ack_tsize   }, /* RFC 2349 */
+    { NULL,      NULL,             NULL             }
+};
+
+
+err_t
+tftpd_init(struct netif *proxy_netif, const char *tftproot)
+{
+    size_t len;
+    err_t error;
+
+    tftpd.root = strdup(tftproot);
+    if (tftpd.root == NULL) {
+        DPRINTF0(("%s: failed to allocate tftpd.root\n", __func__));
+        return ERR_MEM;
+    }
+
+    len = strlen(tftproot);
+    if (tftpd.root[len - 1] == '/') {
+        tftpd.root[len - 1] = '\0';
+    }
+
+    tftpd.pcb = udp_new();
+    if (tftpd.pcb == NULL) {
+        DPRINTF0(("%s: failed to allocate PCB\n", __func__));
+        return ERR_MEM;
+    }
+
+    udp_recv(tftpd.pcb, tftpd_recv, NULL);
+
+    error = udp_bind(tftpd.pcb, &proxy_netif->ip_addr, TFTP_SERVER_PORT);
+    if (error != ERR_OK) {
+        DPRINTF0(("%s: failed to bind PCB\n", __func__));
+        return error;
+    }
+
+    return ERR_OK;
+}
+
+
+static void
+tftpd_recv(void *arg, struct udp_pcb *pcb, struct pbuf *p,
+           ip_addr_t *addr, u16_t port)
+{
+    u16_t op;
+
+    LWIP_ASSERT1(pcb == tftpd.pcb);
+
+    LWIP_UNUSED_ARG(pcb);       /* only in assert */
+    LWIP_UNUSED_ARG(arg);
+
+    if (pbuf_clen(p) > 1) { /* this code assumes contiguous aligned payload */
+        pbuf_free(p);
+        return;
+    }
+
+    op = ntohs(*(u16_t *)p->payload);
+    switch (op) {
+    case TFTP_RRQ:
+        tftpd_rrq(p, addr, port);
+        break;
+
+    case TFTP_WRQ:
+        tftpd_error(addr, port, TFTP_EACCESS, "Permission denied");
+        break;
+
+    default:
+        tftpd_error(addr, port, TFTP_ENOSYS, "Bad opcode %d", op);
+        break;
+    }
+
+    pbuf_free(p);
+}
+
+
+/**
+ * Parse Read Request packet and start new transfer.
+ */
+static void
+tftpd_rrq(struct pbuf *p, ip_addr_t *addr, u16_t port)
+{
+    struct xfer *xfer;
+    char *s;
+    size_t len;
+    int has_options;
+    int status;
+
+    xfer = tftp_xfer_alloc(addr, port);
+    if (xfer == NULL) {
+        return;
+    }
+
+    /* skip opcode */
+    s = (char *)p->payload + sizeof(u16_t);
+    len = p->len - sizeof(u16_t);
+
+
+    /*
+     * Parse RRQ:
+     *   filename, mode, [opt1, value1, [...] ]
+     */
+    status = tftp_parse_filename(xfer, &s, &len);
+    if (status < 0) {
+        goto terminate;
+    }
+
+    status = tftp_parse_mode(xfer, &s, &len);
+    if (status < 0) {
+        goto terminate;
+    }
+
+    has_options = 0;
+    while (len > 0) {
+        status = tftp_parse_option(xfer, &s, &len);
+        if (status < 0) {
+            goto terminate;
+        }
+        has_options += status;
+    }
+
+
+    /*
+     * Create OACK packet if necessary.
+     */
+    if (has_options) {
+        xfer->oack = pbuf_alloc(PBUF_RAW, 128, PBUF_RAM);
+        if (xfer->oack != NULL) {
+            struct tftp_option *o;
+
+            ((u16_t *)xfer->oack->payload)[0] = PP_HTONS(TFTP_OACK);
+
+            s = (char *)xfer->oack->payload + sizeof(u16_t);
+            len = xfer->oack->len - sizeof(u16_t);
+
+            for (o = &tftp_options[0]; o->name != NULL; ++o) {
+                status = (*o->ackopt)(xfer, &s, &len);
+                if (status < 0) {
+                    pbuf_free(xfer->oack);
+                    xfer->oack = NULL;
+                    break;
+                }
+            }
+
+            if (xfer->oack != NULL) {
+                Assert((u16_t)(xfer->oack->len - len) == xfer->oack->len - len);
+                pbuf_realloc(xfer->oack, (u16_t)(xfer->oack->len - len));
+            }
+        }
+    }
+
+
+    /*
+     * Create static pbuf that will be used for all data packets.
+     */
+    xfer->pbuf = pbuf_alloc(PBUF_RAW, xfer->blksize + 4, PBUF_RAM);
+    if (xfer->pbuf == NULL) {
+        tftp_internal_error(xfer);
+        goto terminate;
+    }
+    ((u16_t *)xfer->pbuf->payload)[0] = PP_HTONS(TFTP_DATA);
+
+
+    /*
+     * Finally, create PCB.  Before this point any error was reported
+     * from the server port (see tftp_error() for the reason).
+     */
+    status = tftp_xfer_create_pcb(xfer);
+    if (status < 0) {
+        goto terminate;
+    }
+
+    if (xfer->oack) {
+        tftp_send(xfer);
+    }
+    else {
+        /* trigger send of the first data packet */
+        tftp_recv_ack(xfer, 0);
+    }
+
+    return;
+
+  terminate:
+    DPRINTF(("%s: terminated", __func__));
+    tftp_xfer_free(xfer);
+}
+
+
+static void
+tftp_xfer_recv(void *arg, struct udp_pcb *pcb, struct pbuf *p,
+               ip_addr_t *addr, u16_t port)
+{
+    struct xfer *xfer = (struct xfer *)arg;
+    u16_t op;
+
+    LWIP_UNUSED_ARG(pcb);       /* assert only */
+    LWIP_UNUSED_ARG(addr);
+    LWIP_UNUSED_ARG(port);
+
+    LWIP_ASSERT1(xfer->pcb == pcb);
+
+    if (p->len < 2) {
+        tftp_error(xfer, TFTP_ENOSYS, "Short packet");
+        tftp_xfer_free(xfer);
+        pbuf_free(p);
+        return;
+    }
+
+    op = ntohs(*(u16_t *)p->payload);
+    if (op == TFTP_ACK) {
+        u16_t ack;
+
+        if (p->len < 4) {
+            tftp_error(xfer, TFTP_ENOSYS, "Short packet");
+            tftp_xfer_free(xfer);
+            pbuf_free(p);
+            return;
+        }
+
+        ack = ntohs(((u16_t *)p->payload)[1]);
+        tftp_recv_ack(xfer, ack);
+    }
+    else if (op == TFTP_ERROR) {
+        tftp_xfer_free(xfer);
+    }
+    else {
+        tftp_error(xfer, TFTP_ENOSYS, "Unexpected opcode %d", op);
+        tftp_xfer_free(xfer);
+    }
+
+    pbuf_free(p);
+}
+
+
+static void
+tftp_recv_ack(struct xfer *xfer, u16_t ack)
+{
+    if (ack != (u16_t)xfer->ack) {
+        DPRINTF2(("%s: expect %u (%u), got %u\n",
+                  __func__, (u16_t)xfer->ack, xfer->ack, ack));
+        return;
+    }
+
+    sys_untimeout(tftp_timeout, xfer);
+    xfer->rexmit = 0;
+
+    if (xfer->pbuf->len < xfer->blksize) {
+        DPRINTF(("%s: got final ack %u (%u)\n",
+                 __func__, (u16_t)xfer->ack, xfer->ack));
+        tftp_xfer_free(xfer);
+        return;
+    }
+
+    if (xfer->oack != NULL) {
+        pbuf_free(xfer->oack);
+        xfer->oack = NULL;
+    }
+
+    ++xfer->ack;
+    tftp_fillbuf(xfer);
+    tftp_send(xfer);
+}
+
+
+static void
+tftp_send(struct xfer *xfer)
+{
+    struct pbuf *pbuf;
+
+    pbuf = xfer->oack ? xfer->oack : xfer->pbuf;
+    udp_send(xfer->pcb, pbuf);
+    sys_timeout(xfer->timeout * 1000, tftp_timeout, xfer);
+}
+
+
+static void
+tftp_timeout(void *arg)
+{
+    struct xfer *xfer = (struct xfer *)arg;
+    int maxrexmit;
+
+    maxrexmit = xfer->timeout < 60 ? 5 : 3;
+    if (++xfer->rexmit < maxrexmit) {
+        tftp_send(xfer);
+    }
+    else {
+        tftp_xfer_free(xfer);
+    }
+}
+
+
+static void
+tftp_fillbuf(struct xfer *xfer)
+{
+    ssize_t nread;
+
+    DPRINTF2(("%s: reading block %u\n", __func__, xfer->ack));
+
+    ((u16_t *)xfer->pbuf->payload)[1] = htons(xfer->ack);
+    nread = read(xfer->fd, (char *)xfer->pbuf->payload + 4, xfer->blksize);
+
+    if (nread < 0) {
+        tftp_error(xfer, TFTP_EUNDEF, "Read failed");
+        return;
+    }
+
+    pbuf_realloc(xfer->pbuf, nread + 4);
+}
+
+
+/**
+ * Find a free transfer slot (without a pcb).  Record peer's IP
+ * address and port, but don't allocate a pcb yet.
+ *
+ * We delay creation of the pcb in response to the original request
+ * until the request is verified and accepted.  This makes using
+ * tcpdump(8) easier, since tcpdump does not track TFTP transfers, so
+ * an error reply from a new pcb is not recognized as such and is not
+ * decoded as TFTP (see tftp_error()).
+ *
+ * If the request is rejected, the pcb remains NULL and the transfer
+ * slot remains unallocated.  Since all TFTP processing happens on the
+ * lwIP thread, there's no concurrent processing, so we don't need to
+ * "lock" the transfer slot until the pcb is allocated.
+ */
+static struct xfer *
+tftp_xfer_alloc(ip_addr_t *addr, u16_t port)
+{
+    struct xfer *xfer;
+    int i;
+
+    /* Find free xfer slot */
+    xfer = NULL;
+    for (i = 0; i < TFTP_MAX_XFERS; ++i) {
+        if (tftpd.xfers[i].pcb == NULL) {
+            xfer = &tftpd.xfers[i];
+            break;
+        }
+    }
+
+    if (xfer == NULL) {
+        if (report_transient_errors) {
+            tftpd_error(addr, port, TFTP_EUNDEF,
+                        "Maximum number of simultaneous connections exceeded");
+        }
+        return NULL;
+    }
+
+    ipX_addr_copy(0, xfer->peer_ip, *ip_2_ipX(addr));
+    xfer->peer_port = port;
+
+    xfer->ack = 0;
+
+    xfer->pbuf = NULL;
+    xfer->oack = NULL;
+    xfer->rexmit = 0;
+
+    xfer->blksize = 512;
+    xfer->blksize_from_opt = 0;
+
+    xfer->timeout = 1;
+    xfer->timeout_from_opt = 0;
+
+    xfer->tsize = -1;
+    xfer->tsize_from_opt = 0;
+
+    return xfer;
+}
+
+
+static int
+tftp_xfer_create_pcb(struct xfer *xfer)
+{
+    struct udp_pcb *pcb;
+    err_t error;
+
+    pcb = udp_new();
+
+    /* Bind */
+    if (pcb != NULL) {
+        error = udp_bind(pcb, ipX_2_ip(&tftpd.pcb->local_ip), 0);
+        if (error != ERR_OK) {
+            udp_remove(pcb);
+            pcb = NULL;
+        }
+    }
+
+    /* Connect */
+    if (pcb != NULL) {
+        error = udp_connect(pcb, ipX_2_ip(&xfer->peer_ip), xfer->peer_port);
+        if (error != ERR_OK) {
+            udp_remove(pcb);
+            pcb = NULL;
+        }
+    }
+
+    if (pcb == NULL) {
+        if (report_transient_errors) {
+            tftp_error(xfer, TFTP_EUNDEF, "Failed to create connection");
+        }
+        return -1;
+    }
+
+    xfer->pcb = pcb;
+    udp_recv(xfer->pcb, tftp_xfer_recv, xfer);
+
+    return 0;
+}
+
+
+static void
+tftp_xfer_free(struct xfer *xfer)
+{
+    sys_untimeout(tftp_timeout, xfer);
+
+    if (xfer->pcb != NULL) {
+        udp_remove(xfer->pcb);
+        xfer->pcb = NULL;
+    }
+
+    if (xfer->fd > 0) {
+        close(xfer->fd);
+        xfer->fd = -1;
+    }
+
+    if (xfer->oack != NULL) {
+        pbuf_free(xfer->oack);
+        xfer->oack = NULL;
+    }
+
+    if (xfer->pbuf != NULL) {
+        pbuf_free(xfer->pbuf);
+        xfer->pbuf = NULL;
+    }
+
+    if (xfer->filename != NULL) {
+        free(xfer->filename);
+        xfer->filename = NULL;
+    }
+}
+
+
+static int
+tftp_parse_filename(struct xfer *xfer, char **ps, size_t *plen)
+{
+    const char *filename;
+    struct stat st;
+    char *pathname;
+    char *s;
+    size_t len;
+    int status;
+
+    filename = tftp_getstr(xfer, "filename", ps, plen);
+    if (filename == NULL) {
+        return -1;
+    }
+
+    DPRINTF(("%s: requested file name: %s\n", __func__, filename));
+    xfer->filename = strdup(filename);
+    if (xfer->filename == NULL) {
+        return tftp_internal_error(xfer);
+    }
+
+    /* replace backslashes with forward slashes */
+    s = xfer->filename;
+    while ((s = strchr(s, '\\')) != NULL) {
+        *s++ = '/';
+    }
+
+    /* deny attempts to break out of tftp dir */
+    if (strncmp(xfer->filename, "../", 3) == 0
+        || strstr(xfer->filename, "/../") != NULL)
+    {
+        return tftp_error(xfer, TFTP_ENOENT, "Permission denied");
+    }
+
+    len = strlen(tftpd.root) + 1 /*slash*/ + strlen(xfer->filename) + 1 /*nul*/;
+    pathname = (char *)malloc(len);
+    if (pathname == NULL) {
+        return tftp_internal_error(xfer);
+    }
+
+    RTStrPrintf(pathname, len, "%s/%s", tftpd.root, xfer->filename);
+/** @todo fix RTStrPrintf because this does not currently work:
+ *   status = RTStrPrintf(pathname, len, "%s/%s", tftpd.root, xfer->filename);
+ *   if (status < 0) {
+ *       return tftp_internal_error(xfer);
+ *   }
+ */
+
+    DPRINTF(("%s: full pathname: %s\n", __func__, pathname));
+    xfer->fd = open(pathname, O_RDONLY);
+    if (xfer->fd < 0) {
+        if (errno == EPERM) {
+            return tftp_error(xfer, TFTP_ENOENT, "Permission denied");
+        }
+        else {
+            return tftp_error(xfer, TFTP_ENOENT, "File not found");
+        }
+    }
+
+    status = fstat(xfer->fd, &st);
+    if (status < 0) {
+        return tftp_internal_error(xfer);
+    }
+
+    if (!S_ISREG(st.st_mode)) {
+        return tftp_error(xfer, TFTP_ENOENT, "File not found");
+    }
+
+    xfer->tsize = st.st_size;
+    return 0;
+}
+
+
+static int
+tftp_parse_mode(struct xfer *xfer, char **ps, size_t *plen)
+{
+    const char *modename;
+
+    modename = tftp_getstr(xfer, "mode", ps, plen);
+    if (modename == NULL) {
+        return -1;
+    }
+
+    if (RTStrICmp(modename, "octet") == 0) {
+        xfer->octet = 1;
+    }
+    else if (RTStrICmp(modename, "netascii") == 0) {
+        xfer->octet = 0;
+        /* XXX: not (yet?) */
+        return tftp_error(xfer, TFTP_ENOSYS, "Mode \"netascii\" not supported");
+    }
+    else if (RTStrICmp(modename, "mail") == 0) {
+        return tftp_error(xfer, TFTP_ENOSYS, "Mode \"mail\" not supported");
+    }
+    else {
+        return tftp_error(xfer, TFTP_ENOSYS, "Unknown mode \"%s\"", modename);
+    }
+
+    return 0;
+}
+
+
+static int
+tftp_parse_option(struct xfer *xfer, char **ps, size_t *plen)
+{
+    const char *opt;
+    const char *val;
+    struct tftp_option *o;
+
+    opt = tftp_getstr(xfer, "option name", ps, plen);
+    if (opt == NULL) {
+        return -1;
+    }
+
+    if (*plen == 0) {
+        return tftp_error(xfer, TFTP_EUNDEF, "Missing option value");
+    }
+
+    val = tftp_getstr(xfer, "option value", ps, plen);
+    if (val == NULL) {
+        return -1;
+    }
+
+    /* handle option if known, ignore otherwise */
+    for (o = &tftp_options[0]; o->name != NULL; ++o) {
+        if (RTStrICmp(o->name, opt) == 0) {
+            return (*o->getopt)(xfer, val);
+        }
+    }
+
+    return 0; /* unknown option */
+}
+
+
+static int
+tftp_opt_blksize(struct xfer *xfer, const char *optval)
+{
+    char *end;
+    long blksize;
+
+    errno = 0;
+    blksize = strtol(optval, &end, 10);
+    if (errno != 0 || *end != '\0') {
+        return 0;
+    }
+
+    if (blksize < 8) {
+        return 0;
+    }
+
+    if (blksize > 1428) {       /* exceeds ethernet mtu */
+        blksize = 1428;
+    }
+
+    xfer->blksize = blksize;
+    xfer->blksize_from_opt = 1;
+    return 1;
+}
+
+
+static int
+tftp_opt_timeout(struct xfer *xfer, const char *optval)
+{
+    LWIP_UNUSED_ARG(xfer);
+    LWIP_UNUSED_ARG(optval);
+    return 0;
+}
+
+
+static int
+tftp_opt_tsize(struct xfer *xfer, const char *optval)
+{
+    LWIP_UNUSED_ARG(optval);  /* must be "0", but we don't check it */
+
+    if (xfer->tsize < 0) {
+        return 0;
+    }
+
+    xfer->tsize_from_opt = 1;
+    return 1;
+}
+
+
+static char *
+tftp_getstr(struct xfer *xfer, const char *msg, char **ps, size_t *plen)
+{
+    char *s;
+    ssize_t slen;
+
+    s = *ps;
+    slen = tftp_strnlen(s, *plen);
+    if (slen < 0) {
+        tftp_error(xfer, TFTP_EUNDEF, "Unterminated %s", msg);
+        return NULL;
+    }
+
+    *ps += slen + 1;
+    *plen -= slen + 1;
+
+    return s;
+}
+
+
+static int
+tftp_ack_blksize(struct xfer *xfer, char **ps, size_t *plen)
+{
+    if (!xfer->blksize_from_opt) {
+        return 0;
+    }
+
+    return tftp_add_oack(ps, plen, "blksize", "%u", xfer->blksize);
+}
+
+
+static int
+tftp_ack_timeout(struct xfer *xfer, char **ps, size_t *plen)
+{
+    if (!xfer->timeout_from_opt) {
+        return 0;
+    }
+
+    return tftp_add_oack(ps, plen, "timeout", "%u", xfer->timeout);
+}
+
+
+static int
+tftp_ack_tsize(struct xfer *xfer, char **ps, size_t *plen)
+{
+    if (!xfer->tsize_from_opt) {
+        return 0;
+    }
+
+    LWIP_ASSERT1(xfer->tsize >= 0);
+    return tftp_add_oack(ps, plen, "tsize",
+                         /* XXX: FIXME: want 64 bit */
+                         "%lu", (unsigned long)xfer->tsize);
+}
+
+
+static int
+tftp_add_oack(char **ps, size_t *plen,
+              const char *optname, const char *fmt, ...)
+{
+    va_list ap;
+    int sz;
+
+/** @todo Fix RTStrPrintf because this doesn't really work.
+ *   sz = RTStrPrintf(*ps, *plen, "%s", optname);
+ *   if (sz < 0 || (size_t)sz >= *plen) {
+ *       return -1;
+ *   } */
+    sz = (int)RTStrPrintf(*ps, *plen, "%s", optname);
+    if (/*sz < 0 ||*/ (size_t)sz >= *plen) {
+        return -1;
+    }
+
+    ++sz;                       /* for nul byte */
+    *ps += sz;
+    *plen -= sz;
+
+    va_start(ap, fmt);
+    sz = vsnprintf(*ps, *plen, fmt, ap);
+    va_end(ap);
+    if (sz < 0 || (size_t)sz >= *plen) {
+        return -1;
+    }
+
+    ++sz;                       /* for nul byte */
+    *ps += sz;
+    *plen -= sz;
+
+    return 0;
+}
+
+
+static ssize_t
+tftp_strnlen(char *buf, size_t bufsize)
+{
+    void *end;
+
+    end = memchr(buf, '\0', bufsize);
+    if (end == NULL) {
+        return -1;
+    }
+
+    return (char *)end - buf;
+}
+
+
+static int
+tftp_internal_error(struct xfer *xfer)
+{
+    if (report_transient_errors) {
+        tftp_error(xfer, TFTP_EUNDEF, "Internal error");
+    }
+    return -1;
+}
+
+
+/**
+ * Send an error packet to the peer.
+ *
+ * PCB may not be created yet in which case send the error packet from
+ * the TFTP server port (*).
+ *
+ * (*) We delay creation of the PCB in response to the original
+ * request until the request is verified and accepted.  This makes
+ * using tcpdump(8) easier, since tcpdump does not track TFTP
+ * transfers, so an error reply from a new PCB is not recognized as
+ * such and is not decoded as TFTP.
+ *
+ * Always returns -1 for callers to reuse.
+ */
+static int
+tftp_error(struct xfer *xfer, u16_t error, const char *fmt, ...)
+{
+    va_list ap;
+    struct pbuf *q;
+
+    LWIP_ASSERT1(xfer != NULL);
+
+    va_start(ap, fmt);
+    q = tftp_verror(error, fmt, ap);
+    va_end(ap);
+
+    if (q == NULL) {
+        return -1;
+    }
+
+    if (xfer->pcb != NULL) {
+        udp_send(xfer->pcb, q);
+    }
+    else {
+        udp_sendto(tftpd.pcb, q, ipX_2_ip(&xfer->peer_ip), xfer->peer_port);
+    }
+
+    pbuf_free(q);
+    return -1;
+}
+
+
+/**
+ * Send an error packet from TFTP server port to the specified peer.
+ */
+static void
+tftpd_error(ip_addr_t *addr, u16_t port, u16_t error, const char *fmt, ...)
+{
+    va_list ap;
+    struct pbuf *q;
+
+    va_start(ap, fmt);
+    q = tftp_verror(error, fmt, ap);
+    va_end(ap);
+
+    if (q != NULL) {
+        udp_sendto(tftpd.pcb, q, addr, port);
+        pbuf_free(q);
+    }
+}
+
+
+/**
+ * Create ERROR pbuf with formatted error message.
+ */
+static struct pbuf *
+tftp_verror(u16_t error, const char *fmt, va_list ap)
+{
+    struct tftp_error {
+        u16_t opcode;           /* TFTP_ERROR */
+        u16_t errcode;
+        char errmsg[512];
+    };
+
+    struct pbuf *p;
+    struct tftp_error *errpkt;
+    int msgsz;
+
+    p = pbuf_alloc(PBUF_TRANSPORT, sizeof(*errpkt), PBUF_RAM);
+    if (p == NULL) {
+        return NULL;
+    }
+
+    errpkt = (struct tftp_error *)p->payload;
+    errpkt->opcode = PP_HTONS(TFTP_ERROR);
+    errpkt->errcode = htons(error);
+
+    msgsz = vsnprintf(errpkt->errmsg, sizeof(errpkt->errmsg), fmt, ap);
+    if (msgsz < 0) {
+        errpkt->errmsg[0] = '\0';
+        msgsz = 1;
+    }
+    else if ((size_t)msgsz < sizeof(errpkt->errmsg)) {
+        ++msgsz;                /* for nul byte */
+    }
+    else {
+        msgsz = sizeof(errpkt->errmsg); /* truncated, includes nul byte */
+    }
+
+    pbuf_realloc(p, sizeof(*errpkt) - sizeof(errpkt->errmsg) + msgsz);
+    return p;
+}
diff --git a/src/VBox/NetworkServices/NAT/pxdns.c b/src/VBox/NetworkServices/NAT/pxdns.c
new file mode 100644
index 00000000..5e98824a
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/pxdns.c
@@ -0,0 +1,942 @@
+/* $Id: pxdns.c $ */
+/** @file
+ * NAT Network - DNS proxy.
+ */
+
+/*
+ * Copyright (C) 2009-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+/*
+ * Copyright (c) 2003,2004,2005 Armin Wolfermann
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+#define LOG_GROUP LOG_GROUP_NAT_SERVICE
+
+#include "winutils.h"
+
+#include "proxy.h"
+#include "proxy_pollmgr.h"
+#include "pxtcp.h"
+
+#include "lwip/sys.h"
+#include "lwip/tcpip.h"
+#include "lwip/ip_addr.h"
+#include "lwip/udp.h"
+#include "lwip/tcp.h"
+
+#ifndef RT_OS_WINDOWS
+#include <sys/poll.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <netdb.h>
+#else
+#include "winpoll.h"
+#endif
+
+#include <stdio.h>
+#include <string.h>
+
+
+union sockaddr_inet {
+    struct sockaddr sa;
+    struct sockaddr_in sin;
+    struct sockaddr_in6 sin6;
+};
+
+
+struct request;
+
+
+/**
+ * DNS Proxy
+ */
+struct pxdns {
+    SOCKET sock4;
+    SOCKET sock6;
+
+    struct pollmgr_handler pmhdl4;
+    struct pollmgr_handler pmhdl6;
+
+    struct udp_pcb *pcb4;
+    struct udp_pcb *pcb6;
+
+    struct tcp_pcb *ltcp;
+
+    size_t generation;
+    size_t nresolvers;
+    union sockaddr_inet *resolvers;
+
+    u16_t id;
+
+    sys_mutex_t lock;
+
+    size_t active_queries;
+    size_t expired_queries;
+    size_t late_answers;
+    size_t hash_collisions;
+
+#define TIMEOUT 5
+    size_t timeout_slot;
+    u32_t timeout_mask;
+    struct request *timeout_list[TIMEOUT];
+
+#define HASHSIZE 10
+#define HASH(id) ((id) & ((1 << HASHSIZE) - 1))
+    struct request *request_hash[1 << HASHSIZE];
+} g_pxdns;
+
+
+struct request {
+    /**
+     * Request ID that we use in relayed request.
+     */
+    u16_t id;
+
+    /**
+     * pxdns::generation used for this request
+     */
+    size_t generation;
+
+    /**
+     * Current index into pxdns::resolvers
+     */
+    size_t residx;
+
+    /**
+     * PCB from which we have received this request.  lwIP doesn't
+     * support listening for both IPv4 and IPv6 on the same pcb, so we
+     * use two and need to keep track.
+     */
+    struct udp_pcb *pcb;
+
+    /**
+     * Client this request is from and its original request ID.
+     */
+    ipX_addr_t client_addr;
+    u16_t client_port;
+    u16_t client_id;
+
+    /**
+     * Chaining for pxdns::request_hash
+     */
+    struct request **pprev_hash;
+    struct request *next_hash;
+
+    /**
+     * Chaining for pxdns::timeout_list
+     */
+    struct request **pprev_timeout;
+    struct request *next_timeout;
+
+    /**
+     * Slot in pxdns::timeout_list
+     */
+    size_t timeout_slot;
+
+    /**
+     * Pbuf with reply received on pollmgr thread.
+     */
+    struct pbuf *reply;
+
+    /**
+     * Preallocated lwIP message to send reply from the lwIP thread.
+     */
+    struct tcpip_msg msg_reply;
+
+    /**
+     * Client request.  ID is replaced with ours, original saved in
+     * client_id.  Use a copy since we might need to resend and we
+     * don't want to hold onto pbuf of the request.
+     */
+    size_t size;
+    u8_t data[1];
+};
+
+
+static void pxdns_create_resolver_sockaddrs(struct pxdns *pxdns,
+                                            const char **nameservers);
+
+static err_t pxdns_accept_syn(void *arg, struct tcp_pcb *newpcb, struct pbuf *syn);
+
+static void pxdns_recv4(void *arg, struct udp_pcb *pcb, struct pbuf *p,
+                        ip_addr_t *addr, u16_t port);
+static void pxdns_recv6(void *arg, struct udp_pcb *pcb, struct pbuf *p,
+                        ip6_addr_t *addr, u16_t port);
+static void pxdns_query(struct pxdns *pxdns, struct udp_pcb *pcb, struct pbuf *p,
+                        ipX_addr_t *addr, u16_t port);
+static void pxdns_timer(void *arg);
+static int pxdns_rexmit(struct pxdns *pxdns, struct request *req);
+static int pxdns_forward_outbound(struct pxdns *pxdns, struct request *req);
+
+static int pxdns_pmgr_pump(struct pollmgr_handler *handler, SOCKET fd, int revents);
+static void pxdns_pcb_reply(void *ctx);
+
+static void pxdns_request_register(struct pxdns *pxdns, struct request *req);
+static void pxdns_request_deregister(struct pxdns *pxdns, struct request *req);
+static struct request *pxdns_request_find(struct pxdns *pxdns, u16_t id);
+
+static void pxdns_hash_add(struct pxdns *pxdns, struct request *req);
+static void pxdns_hash_del(struct pxdns *pxdns, struct request *req);
+static void pxdns_timeout_add(struct pxdns *pxdns, struct request *req);
+static void pxdns_timeout_del(struct pxdns *pxdns, struct request *req);
+
+static void pxdns_request_free(struct request *req);
+
+
+err_t
+pxdns_init(struct netif *proxy_netif)
+{
+    struct pxdns *pxdns = &g_pxdns;
+    err_t error;
+
+    LWIP_UNUSED_ARG(proxy_netif);
+
+    pxdns->ltcp = tcp_new();
+    if (pxdns->ltcp != NULL) {
+        tcp_bind_ip6(pxdns->ltcp, IP6_ADDR_ANY, 53);
+        pxdns->ltcp = tcp_listen_dual(pxdns->ltcp);
+        if (pxdns->ltcp != NULL) {
+            tcp_arg(pxdns->ltcp, pxdns);
+            tcp_accept_syn(pxdns->ltcp, pxdns_accept_syn);
+        }
+    }
+
+    pxdns->pmhdl4.callback = pxdns_pmgr_pump;
+    pxdns->pmhdl4.data = (void *)pxdns;
+    pxdns->pmhdl4.slot = -1;
+
+    pxdns->pmhdl6.callback = pxdns_pmgr_pump;
+    pxdns->pmhdl6.data = (void *)pxdns;
+    pxdns->pmhdl6.slot = -1;
+
+    pxdns->pcb4 = udp_new();
+    if (pxdns->pcb4 == NULL) {
+        error = ERR_MEM;
+        goto err_cleanup_pcb;
+    }
+
+    pxdns->pcb6 = udp_new_ip6();
+    if (pxdns->pcb6 == NULL) {
+        error = ERR_MEM;
+        goto err_cleanup_pcb;
+    }
+
+    error = udp_bind(pxdns->pcb4, IP_ADDR_ANY, 53);
+    if (error != ERR_OK) {
+        goto err_cleanup_pcb;
+    }
+
+    error = udp_bind_ip6(pxdns->pcb6, IP6_ADDR_ANY, 53);
+    if (error != ERR_OK) {
+        goto err_cleanup_pcb;
+    }
+
+    udp_recv(pxdns->pcb4, pxdns_recv4, pxdns);
+    udp_recv_ip6(pxdns->pcb6, pxdns_recv6, pxdns);
+
+    pxdns->sock4 = socket(AF_INET, SOCK_DGRAM, 0);
+    if (pxdns->sock4 == INVALID_SOCKET) {
+        goto err_cleanup_pcb;
+    }
+
+    pxdns->sock6 = socket(AF_INET6, SOCK_DGRAM, 0);
+    if (pxdns->sock6 == INVALID_SOCKET) {
+        /* it's ok if the host doesn't support IPv6 */
+        /* XXX: TODO: log */
+    }
+
+    pxdns->generation = 0;
+    pxdns->nresolvers = 0;
+    pxdns->resolvers = NULL;
+    pxdns_create_resolver_sockaddrs(pxdns, g_proxy_options->nameservers);
+
+    sys_mutex_new(&pxdns->lock);
+
+    pxdns->timeout_slot = 0;
+    pxdns->timeout_mask = 0;
+
+    /* NB: assumes pollmgr thread is not running yet */
+    pollmgr_add(&pxdns->pmhdl4, pxdns->sock4, POLLIN);
+    if (pxdns->sock6 != INVALID_SOCKET) {
+        pollmgr_add(&pxdns->pmhdl6, pxdns->sock6, POLLIN);
+    }
+
+    return ERR_OK;
+
+  err_cleanup_pcb:
+    if (pxdns->pcb4 != NULL) {
+        udp_remove(pxdns->pcb4);
+        pxdns->pcb4 = NULL;
+    }
+    if (pxdns->pcb6 != NULL) {
+        udp_remove(pxdns->pcb6);
+        pxdns->pcb4 = NULL;
+    }
+
+    return error;
+}
+
+
+/**
+ * lwIP thread callback to set the new list of nameservers.
+ */
+void
+pxdns_set_nameservers(void *arg)
+{
+    const char **nameservers = (const char **)arg;
+
+    if (g_proxy_options->nameservers != NULL) {
+        RTMemFree((void *)g_proxy_options->nameservers);
+    }
+    g_proxy_options->nameservers = nameservers;
+
+    pxdns_create_resolver_sockaddrs(&g_pxdns, nameservers);
+}
+
+
+/**
+ * Use this list of nameservers to resolve guest requests.
+ *
+ * Runs on lwIP thread, so no new queries or retramsmits compete with
+ * it for the use of the existing list of resolvers (to be replaced).
+ */
+static void
+pxdns_create_resolver_sockaddrs(struct pxdns *pxdns, const char **nameservers)
+{
+    struct addrinfo hints;
+    union sockaddr_inet *resolvers;
+    size_t nnames, nresolvers;
+    const char **p;
+    int status;
+
+    resolvers = NULL;
+    nresolvers = 0;
+
+    if (nameservers == NULL) {
+        goto update_resolvers;
+    }
+
+    nnames = 0;
+    for (p = nameservers; *p != NULL; ++p) {
+        ++nnames;
+    }
+
+    if (nnames == 0) {
+        goto update_resolvers;
+    }
+
+    resolvers = (union sockaddr_inet *)calloc(sizeof(resolvers[0]), nnames);
+    if (resolvers == NULL) {
+        nresolvers = 0;
+        goto update_resolvers;
+    }
+
+    memset(&hints, 0, sizeof(hints));
+    hints.ai_family = AF_UNSPEC;
+    hints.ai_socktype = SOCK_DGRAM;
+    hints.ai_flags = AI_NUMERICHOST | AI_NUMERICSERV;
+
+    for (p = nameservers; *p != NULL; ++p) {
+        const char *name = *p;
+        struct addrinfo *ai;
+        status = getaddrinfo(name, /* "domain" */ "53", &hints, &ai);
+        if (status != 0) {
+            /* XXX: log failed resolution */
+            continue;
+        }
+
+        if (ai->ai_family != AF_INET && ai->ai_family != AF_INET6) {
+            /* XXX: log unsupported address family */
+            freeaddrinfo(ai);
+            continue;
+        }
+
+        if (ai->ai_addrlen > sizeof(resolvers[nresolvers])) {
+            /* XXX: log */
+            freeaddrinfo(ai);
+            continue;
+        }
+
+        if (ai->ai_family == AF_INET6 && pxdns->sock6 == INVALID_SOCKET) {
+            /* no IPv6 support on the host, can't use this resolver */
+            freeaddrinfo(ai);
+            continue;
+        }
+
+        memcpy(&resolvers[nresolvers], ai->ai_addr, ai->ai_addrlen);
+        freeaddrinfo(ai);
+        ++nresolvers;
+    }
+
+    if (nresolvers == 0) {
+        if (resolvers != NULL) {
+            free(resolvers);
+        }
+        resolvers = NULL;
+    }
+
+  update_resolvers:
+    ++pxdns->generation;
+    if (pxdns->resolvers != NULL) {
+        free(pxdns->resolvers);
+    }
+    pxdns->resolvers = resolvers;
+    pxdns->nresolvers = nresolvers;
+}
+
+
+static void
+pxdns_request_free(struct request *req)
+{
+    LWIP_ASSERT1(req->pprev_hash == NULL);
+    LWIP_ASSERT1(req->pprev_timeout == NULL);
+
+    if (req->reply != NULL) {
+        pbuf_free(req->reply);
+    }
+    free(req);
+}
+
+
+static void
+pxdns_hash_add(struct pxdns *pxdns, struct request *req)
+{
+    struct request **chain;
+
+    LWIP_ASSERT1(req->pprev_hash == NULL);
+    ++pxdns->active_queries;
+
+    chain = &pxdns->request_hash[HASH(req->id)];
+    if ((req->next_hash = *chain) != NULL) {
+        (*chain)->pprev_hash = &req->next_hash;
+        ++pxdns->hash_collisions;
+    }
+    *chain = req;
+    req->pprev_hash = chain;
+}
+
+
+static void
+pxdns_timeout_add(struct pxdns *pxdns, struct request *req)
+{
+    struct request **chain;
+    u32_t omask;
+
+    LWIP_ASSERT1(req->pprev_timeout == NULL);
+
+    req->timeout_slot = pxdns->timeout_slot;
+    chain = &pxdns->timeout_list[req->timeout_slot];
+    if ((req->next_timeout = *chain) != NULL) {
+        (*chain)->pprev_timeout = &req->next_timeout;
+    }
+    *chain = req;
+    req->pprev_timeout = chain;
+
+    omask = pxdns->timeout_mask;
+    pxdns->timeout_mask |= 1U << req->timeout_slot;
+    if (omask == 0) {
+        sys_untimeout(pxdns_timer, pxdns);
+        sys_timeout(1 * 1000, pxdns_timer, pxdns);
+    }
+}
+
+
+static void
+pxdns_hash_del(struct pxdns *pxdns, struct request *req)
+{
+    LWIP_ASSERT1(req->pprev_hash != NULL);
+    --pxdns->active_queries;
+
+    if (req->next_hash != NULL) {
+        req->next_hash->pprev_hash = req->pprev_hash;
+    }
+    *req->pprev_hash = req->next_hash;
+    req->pprev_hash = NULL;
+    req->next_hash = NULL;
+}
+
+
+static void
+pxdns_timeout_del(struct pxdns *pxdns, struct request *req)
+{
+    LWIP_ASSERT1(req->pprev_timeout != NULL);
+    LWIP_ASSERT1(req->timeout_slot < TIMEOUT);
+
+    if (req->next_timeout != NULL) {
+        req->next_timeout->pprev_timeout = req->pprev_timeout;
+    }
+    *req->pprev_timeout = req->next_timeout;
+    req->pprev_timeout = NULL;
+    req->next_timeout = NULL;
+
+    if (pxdns->timeout_list[req->timeout_slot] == NULL) {
+        pxdns->timeout_mask &= ~(1U << req->timeout_slot);
+        /* may be on pollmgr thread so no sys_untimeout */
+    }
+}
+
+
+
+/**
+ * Do bookkeeping on new request.  Called from pxdns_query().
+ */
+static void
+pxdns_request_register(struct pxdns *pxdns, struct request *req)
+{
+    sys_mutex_lock(&pxdns->lock);
+
+    pxdns_hash_add(pxdns, req);
+    pxdns_timeout_add(pxdns, req);
+
+    sys_mutex_unlock(&pxdns->lock);
+}
+
+
+static void
+pxdns_request_deregister(struct pxdns *pxdns, struct request *req)
+{
+    sys_mutex_lock(&pxdns->lock);
+
+    pxdns_hash_del(pxdns, req);
+    pxdns_timeout_del(pxdns, req);
+
+    sys_mutex_unlock(&pxdns->lock);
+}
+
+
+/**
+ * Find request by the id we used when relaying it and remove it from
+ * id hash and timeout list.  Called from pxdns_pmgr_pump() when reply
+ * comes.
+ */
+static struct request *
+pxdns_request_find(struct pxdns *pxdns, u16_t id)
+{
+    struct request *req = NULL;
+
+    sys_mutex_lock(&pxdns->lock);
+
+    /* find request in the id->req hash */
+    for (req = pxdns->request_hash[HASH(id)]; req != NULL; req = req->next_hash) {
+        if (req->id == id) {
+            break;
+        }
+    }
+
+    if (req != NULL) {
+        pxdns_hash_del(pxdns, req);
+        pxdns_timeout_del(pxdns, req);
+    }
+
+    sys_mutex_unlock(&pxdns->lock);
+    return req;
+}
+
+
+/**
+ * Retransmit of g/c expired requests and move timeout slot forward.
+ */
+static void
+pxdns_timer(void *arg)
+{
+    struct pxdns *pxdns = (struct pxdns *)arg;
+    struct request **chain, *req;
+    u32_t mask;
+
+    sys_mutex_lock(&pxdns->lock);
+
+    /*
+     * Move timeout slot first.  New slot points to the list of
+     * expired requests.  If any expired request is retransmitted, we
+     * keep it on the list (that is now current), effectively
+     * resetting the timeout.
+     */
+    LWIP_ASSERT1(pxdns->timeout_slot < TIMEOUT);
+    if (++pxdns->timeout_slot == TIMEOUT) {
+        pxdns->timeout_slot = 0;
+    }
+
+    chain = &pxdns->timeout_list[pxdns->timeout_slot];
+    req = *chain;
+    while (req != NULL) {
+        struct request *expired = req;
+        req = req->next_timeout;
+
+        if (pxdns_rexmit(pxdns, expired)) {
+            continue;
+        }
+
+        pxdns_hash_del(pxdns, expired);
+        pxdns_timeout_del(pxdns, expired);
+        ++pxdns->expired_queries;
+
+        pxdns_request_free(expired);
+    }
+
+    if (pxdns->timeout_list[pxdns->timeout_slot] == NULL) {
+        pxdns->timeout_mask &= ~(1U << pxdns->timeout_slot);
+    }
+    else {
+        pxdns->timeout_mask |= 1U << pxdns->timeout_slot;
+    }
+    mask = pxdns->timeout_mask;
+
+    sys_mutex_unlock(&pxdns->lock);
+
+    if (mask != 0) {
+        sys_timeout(1 * 1000, pxdns_timer, pxdns);
+    }
+}
+
+
+static void
+pxdns_recv4(void *arg, struct udp_pcb *pcb, struct pbuf *p,
+            ip_addr_t *addr, u16_t port)
+{
+    struct pxdns *pxdns = (struct pxdns *)arg;
+    pxdns_query(pxdns, pcb, p, ip_2_ipX(addr), port);
+}
+
+static void
+pxdns_recv6(void *arg, struct udp_pcb *pcb, struct pbuf *p,
+            ip6_addr_t *addr, u16_t port)
+{
+    struct pxdns *pxdns = (struct pxdns *)arg;
+    pxdns_query(pxdns, pcb, p, ip6_2_ipX(addr), port);
+}
+
+
+static void
+pxdns_query(struct pxdns *pxdns, struct udp_pcb *pcb, struct pbuf *p,
+            ipX_addr_t *addr, u16_t port)
+{
+    struct request *req;
+    int sent;
+
+    if (pxdns->nresolvers == 0) {
+        /* nothing we can do */
+        pbuf_free(p);
+        return;
+    }
+
+    req = calloc(1, sizeof(struct request) - 1 + p->tot_len);
+    if (req == NULL) {
+        pbuf_free(p);
+        return;
+    }
+
+    /* copy request data */
+    req->size = p->tot_len;
+    pbuf_copy_partial(p, req->data, p->tot_len, 0);
+
+    /* save client identity and client's request id */
+    req->pcb = pcb;
+    ipX_addr_copy(PCB_ISIPV6(pcb), req->client_addr, *addr);
+    req->client_port = port;
+    memcpy(&req->client_id, req->data, sizeof(req->client_id));
+
+    /* slap our request id onto it */
+    req->id = pxdns->id++;
+    memcpy(req->data, &req->id, sizeof(u16_t));
+
+    /* resolver to forward to */
+    req->generation = pxdns->generation;
+    req->residx = 0;
+
+    /* prepare for relaying the reply back to guest */
+    req->msg_reply.type = TCPIP_MSG_CALLBACK_STATIC;
+    req->msg_reply.sem = NULL;
+    req->msg_reply.msg.cb.function = pxdns_pcb_reply;
+    req->msg_reply.msg.cb.ctx = (void *)req;
+
+    DPRINTF2(("%s: req=%p: client id %d -> id %d\n",
+              __func__, (void *)req, req->client_id, req->id));
+
+    pxdns_request_register(pxdns, req);
+
+    sent = pxdns_forward_outbound(pxdns, req);
+    if (!sent) {
+        sent = pxdns_rexmit(pxdns, req);
+    }
+    if (!sent) {
+        pxdns_request_deregister(pxdns, req);
+        pxdns_request_free(req);
+    }
+}
+
+
+/**
+ * Forward request to the req::residx resolver in the pxdns::resolvers
+ * array of upstream resolvers.
+ *
+ * Returns 1 on success, 0 on failure.
+ */
+static int
+pxdns_forward_outbound(struct pxdns *pxdns, struct request *req)
+{
+    union sockaddr_inet *resolver;
+    ssize_t nsent;
+#ifdef RT_OS_WINDOWS
+    const char *pSendData = (const char *)&req->data[0];
+    int         cbSendData = (int)req->size;
+    Assert((size_t)cbSendData == req->size);
+#else
+    const void *pSendData = &req->data[0];
+    size_t      cbSendData = req->size;
+#endif
+
+    DPRINTF2(("%s: req %p: sending to resolver #%lu\n",
+              __func__, (void *)req, (unsigned long)req->residx));
+
+    LWIP_ASSERT1(req->generation == pxdns->generation);
+    LWIP_ASSERT1(req->residx < pxdns->nresolvers);
+    resolver = &pxdns->resolvers[req->residx];
+
+    if (resolver->sa.sa_family == AF_INET) {
+        nsent = sendto(pxdns->sock4, pSendData, cbSendData, 0,
+                       &resolver->sa, sizeof(resolver->sin));
+
+    }
+    else if (resolver->sa.sa_family == AF_INET6) {
+        if (pxdns->sock6 != INVALID_SOCKET) {
+            nsent = sendto(pxdns->sock6, pSendData, cbSendData, 0,
+                           &resolver->sa, sizeof(resolver->sin6));
+        }
+        else {
+            /* shouldn't happen, we should have weeded out IPv6 resolvers */
+            return 0;
+        }
+    }
+    else {
+        /* shouldn't happen, we should have weeded out unsupported families */
+        return 0;
+    }
+
+    if ((size_t)nsent == req->size) {
+        return 1; /* sent */
+    }
+
+    if (nsent < 0) {
+        DPRINTF2(("%s: send: %R[sockerr]\n", __func__, SOCKERRNO()));
+    }
+    else {
+        DPRINTF2(("%s: sent only %lu of %lu\n",
+                  __func__, (unsigned long)nsent, (unsigned long)req->size));
+    }
+    return 0; /* not sent, caller will retry as necessary */
+}
+
+
+/**
+ * Forward request to the next resolver in the pxdns::resolvers array
+ * of upstream resolvers if there are any left.
+ */
+static int
+pxdns_rexmit(struct pxdns *pxdns, struct request *req)
+{
+    int sent;
+
+    if (/* __predict_false */ req->generation != pxdns->generation) {
+        DPRINTF2(("%s: req %p: generation %lu != pxdns generation %lu\n",
+                  __func__, (void *)req,
+                  (unsigned long)req->generation,
+                  (unsigned long)pxdns->generation));
+        return 0;
+    }
+
+    LWIP_ASSERT1(req->residx < pxdns->nresolvers);
+    do {
+        if (++req->residx == pxdns->nresolvers) {
+            return 0;
+        }
+
+        sent = pxdns_forward_outbound(pxdns, req);
+    } while (!sent);
+
+    return 1;
+}
+
+
+static int
+pxdns_pmgr_pump(struct pollmgr_handler *handler, SOCKET fd, int revents)
+{
+    struct pxdns *pxdns;
+    struct request *req;
+    ssize_t nread;
+    err_t error;
+    u16_t id;
+
+    pxdns = (struct pxdns *)handler->data;
+    LWIP_ASSERT1(handler == &pxdns->pmhdl4 || handler == &pxdns->pmhdl6);
+    LWIP_ASSERT1(fd == (handler == &pxdns->pmhdl4 ? pxdns->sock4 : pxdns->sock6));
+
+    if (revents & ~(POLLIN|POLLERR)) {
+        DPRINTF0(("%s: unexpected revents 0x%x\n", __func__, revents));
+        return POLLIN;
+    }
+
+    if (revents & POLLERR) {
+        int sockerr = -1;
+        socklen_t optlen = (socklen_t)sizeof(sockerr);
+        int status;
+
+        status = getsockopt(fd, SOL_SOCKET,
+                            SO_ERROR, (char *)&sockerr, &optlen);
+        if (status < 0) {
+            DPRINTF(("%s: sock %d: SO_ERROR failed: %R[sockerr]\n",
+                     __func__, fd, SOCKERRNO()));
+        }
+        else {
+            DPRINTF(("%s: sock %d: %R[sockerr]\n",
+                     __func__, fd, sockerr));
+        }
+    }
+
+    if ((revents & POLLIN) == 0) {
+        return POLLIN;
+    }
+
+
+#ifdef RT_OS_WINDOWS
+    nread = recv(fd, (char *)pollmgr_udpbuf, sizeof(pollmgr_udpbuf), 0);
+#else
+    nread = recv(fd, pollmgr_udpbuf, sizeof(pollmgr_udpbuf), 0);
+#endif
+    if (nread < 0) {
+        DPRINTF(("%s: %R[sockerr]\n", __func__, SOCKERRNO()));
+        return POLLIN;
+    }
+
+    /* check for minimum dns packet length */
+    if (nread < 12) {
+        DPRINTF2(("%s: short reply %lu bytes\n",
+                  __func__, (unsigned long)nread));
+        return POLLIN;
+    }
+
+    /* XXX: shall we proxy back RCODE=Refused responses? */
+
+    memcpy(&id, pollmgr_udpbuf, sizeof(id));
+    req = pxdns_request_find(pxdns, id);
+    if (req == NULL) {
+        DPRINTF2(("%s: orphaned reply for %d\n", __func__, id));
+        ++pxdns->late_answers;
+        return POLLIN;
+    }
+
+    DPRINTF2(("%s: reply for req=%p: id %d -> client id %d\n",
+              __func__, (void *)req, req->id, req->client_id));
+
+    req->reply = pbuf_alloc(PBUF_RAW, nread, PBUF_RAM);
+    if (req->reply == NULL) {
+        DPRINTF(("%s: pbuf_alloc(%d) failed\n", __func__, (int)nread));
+        pxdns_request_free(req);
+        return POLLIN;
+    }
+
+    memcpy(pollmgr_udpbuf, &req->client_id, sizeof(req->client_id));
+    error = pbuf_take(req->reply, pollmgr_udpbuf, nread);
+    if (error != ERR_OK) {
+        DPRINTF(("%s: pbuf_take(%d) failed\n", __func__, (int)nread));
+        pxdns_request_free(req);
+        return POLLIN;
+    }
+
+    proxy_lwip_post(&req->msg_reply);
+    return POLLIN;
+}
+
+
+/**
+ * Called on lwIP thread via request::msg_reply callback.
+ */
+static void
+pxdns_pcb_reply(void *ctx)
+{
+    struct request *req = (struct request *)ctx;
+    err_t error;
+
+    error = udp_sendto(req->pcb, req->reply,
+                       ipX_2_ip(&req->client_addr), req->client_port);
+    if (error != ERR_OK) {
+        DPRINTF(("%s: udp_sendto err %s\n",
+                 __func__, proxy_lwip_strerr(error)));
+    }
+
+    pxdns_request_free(req);
+}
+
+
+/**
+ * TCP DNS proxy.  This kicks in for large replies that don't fit into
+ * 512 bytes of UDP payload.  Client will retry with TCP to get
+ * complete reply.
+ */
+static err_t
+pxdns_accept_syn(void *arg, struct tcp_pcb *newpcb, struct pbuf *syn)
+{
+    struct pxdns *pxdns = (struct pxdns *)arg;
+    union sockaddr_inet *si;
+    ipX_addr_t *dst;
+    u16_t dst_port;
+
+    tcp_accepted(pxdns->ltcp);
+
+    if (pxdns->nresolvers == 0) {
+        return ERR_CONN;
+    }
+
+    si = &pxdns->resolvers[0];
+
+    if (si->sa.sa_family == AF_INET6) {
+        dst = (ipX_addr_t *)&si->sin6.sin6_addr;
+        dst_port = ntohs(si->sin6.sin6_port);
+    }
+    else {
+        dst = (ipX_addr_t *)&si->sin.sin_addr;
+        dst_port = ntohs(si->sin.sin_port);
+    }
+
+    /*
+     * XXX: TODO: need to implement protocol hooks.  E.g. here if
+     * connect fails, we should try connecting to a different server.
+     */
+    return pxtcp_pcb_accept_outbound(newpcb, syn,
+               si->sa.sa_family == AF_INET6, dst, dst_port);
+}
diff --git a/src/VBox/NetworkServices/NAT/pxping.c b/src/VBox/NetworkServices/NAT/pxping.c
new file mode 100644
index 00000000..9acee074
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/pxping.c
@@ -0,0 +1,2020 @@
+/* $Id: pxping.c $ */
+/** @file
+ * NAT Network - ping proxy, raw sockets version.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#define LOG_GROUP LOG_GROUP_NAT_SERVICE
+
+#include "winutils.h"
+#include "proxy.h"
+#include "proxy_pollmgr.h"
+#include "pxremap.h"
+
+#include <iprt/string.h>
+
+#ifndef RT_OS_WINDOWS
+#include <sys/types.h>
+#include <sys/socket.h>
+#ifdef RT_OS_DARWIN
+# define __APPLE_USE_RFC_3542
+#endif
+#include <netinet/in.h>
+#include <poll.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#else
+#include <iprt/stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include "winpoll.h"
+#endif
+
+#include "lwip/opt.h"
+
+#include "lwip/sys.h"
+#include "lwip/tcpip.h"
+#include "lwip/inet_chksum.h"
+#include "lwip/ip.h"
+#include "lwip/icmp.h"
+
+#if defined(RT_OS_LINUX) && !defined(__USE_GNU)
+#if __GLIBC_PREREQ(2, 8)
+/*
+ * XXX: This is gross.  in6_pktinfo is now hidden behind _GNU_SOURCE
+ * https://sourceware.org/bugzilla/show_bug.cgi?id=6775
+ *
+ * But in older glibc versions, e.g. RHEL5, it is not!  I don't want
+ * to deal with _GNU_SOURCE now, so as a kludge check for glibc
+ * version.  It seems the __USE_GNU guard was introduced in 2.8.
+ */
+struct in6_pktinfo {
+    struct in6_addr ipi6_addr;
+    unsigned int ipi6_ifindex;
+};
+#endif  /* __GLIBC_PREREQ */
+#endif  /* RT_OS_LINUX && !__USE_GNU */
+
+
+/* forward */
+struct ping_pcb;
+
+
+/**
+ * Global state for ping proxy collected in one entity to minimize
+ * globals.  There's only one instance of this structure.
+ *
+ * Raw ICMP sockets are promiscuous, so it doesn't make sense to have
+ * multiple.  If this code ever needs to support multiple netifs, the
+ * netif member should be exiled into "pcb".
+ */
+struct pxping {
+    SOCKET sock4;
+
+#if defined(RT_OS_DARWIN) || defined(RT_OS_SOLARIS)
+#   define DF_WITH_IP_HDRINCL
+    int hdrincl;
+#else
+    int df;
+#endif
+    int ttl;
+    int tos;
+
+    SOCKET sock6;
+#ifdef RT_OS_WINDOWS
+    LPFN_WSARECVMSG pfWSARecvMsg6;
+#endif
+    int hopl;
+
+    struct pollmgr_handler pmhdl4;
+    struct pollmgr_handler pmhdl6;
+
+    struct netif *netif;
+
+    /**
+     * Protect lwIP and pmgr accesses to the list of pcbs.
+     */
+    sys_mutex_t lock;
+
+    /*
+     * We need to find pcbs both from the guest side and from the host
+     * side.  If we need to support industrial grade ping throughput,
+     * we will need two pcb hashes.  For now, a short linked list
+     * should be enough.  Cf. pxping_pcb_for_request() and
+     * pxping_pcb_for_reply().
+     */
+#define PXPING_MAX_PCBS 8
+    size_t npcbs;
+    struct ping_pcb *pcbs;
+
+#define TIMEOUT 5
+    int timer_active;
+    size_t timeout_slot;
+    struct ping_pcb *timeout_list[TIMEOUT];
+};
+
+
+/**
+ * Quasi PCB for ping.
+ */
+struct ping_pcb {
+    ipX_addr_t src;
+    ipX_addr_t dst;
+
+    u8_t is_ipv6;
+    u8_t is_mapped;
+
+    u16_t guest_id;
+    u16_t host_id;
+
+    /**
+     * Desired slot in pxping::timeout_list.  See pxping_timer().
+     */
+    size_t timeout_slot;
+
+    /**
+     * Chaining for pxping::timeout_list
+     */
+    struct ping_pcb **pprev_timeout;
+    struct ping_pcb *next_timeout;
+
+    /**
+     * Chaining for pxping::pcbs
+     */
+    struct ping_pcb *next;
+
+    union {
+        struct sockaddr_in sin;
+        struct sockaddr_in6 sin6;
+    } peer;
+};
+
+
+/**
+ * lwIP thread callback message for IPv4 ping.
+ *
+ * We pass raw IP datagram for ip_output_if() so we only need pbuf and
+ * netif (from pxping).
+ */
+struct ping_msg {
+    struct tcpip_msg msg;
+    struct pxping *pxping;
+    struct pbuf *p;
+};
+
+
+/**
+ * lwIP thread callback message for IPv6 ping.
+ *
+ * We cannot obtain raw IPv6 datagram from host without extra trouble,
+ * so we pass ICMPv6 payload in pbuf and also other parameters to
+ * ip6_output_if().
+ */
+struct ping6_msg {
+    struct tcpip_msg msg;
+    struct pxping *pxping;
+    struct pbuf *p;
+    ip6_addr_t src, dst;
+    int hopl, tclass;
+};
+
+
+#ifdef RT_OS_WINDOWS
+static int pxping_init_windows(struct pxping *pxping);
+#endif
+static void pxping_recv4(void *arg, struct pbuf *p);
+static void pxping_recv6(void *arg, struct pbuf *p);
+
+static void pxping_timer(void *arg);
+static void pxping_timer_needed(struct pxping *pxping);
+
+static struct ping_pcb *pxping_pcb_for_request(struct pxping *pxping,
+                                               int is_ipv6,
+                                               ipX_addr_t *src, ipX_addr_t *dst,
+                                               u16_t guest_id);
+static struct ping_pcb *pxping_pcb_for_reply(struct pxping *pxping, int is_ipv6,
+                                             ipX_addr_t *dst, u16_t host_id);
+
+static FNRTSTRFORMATTYPE pxping_pcb_rtstrfmt;
+static struct ping_pcb *pxping_pcb_allocate(struct pxping *pxping);
+static void pxping_pcb_register(struct pxping *pxping, struct ping_pcb *pcb);
+static void pxping_pcb_deregister(struct pxping *pxping, struct ping_pcb *pcb);
+static void pxping_pcb_delete(struct pxping *pxping, struct ping_pcb *pcb);
+static void pxping_timeout_add(struct pxping *pxping, struct ping_pcb *pcb);
+static void pxping_timeout_del(struct pxping *pxping, struct ping_pcb *pcb);
+
+static int pxping_pmgr_pump(struct pollmgr_handler *handler, SOCKET fd, int revents);
+
+static void pxping_pmgr_icmp4(struct pxping *pxping);
+static void pxping_pmgr_icmp4_echo(struct pxping *pxping,
+                                   u16_t iplen, struct sockaddr_in *peer);
+static void pxping_pmgr_icmp4_error(struct pxping *pxping,
+                                    u16_t iplen, struct sockaddr_in *peer);
+static void pxping_pmgr_icmp6(struct pxping *pxping);
+static void pxping_pmgr_icmp6_echo(struct pxping *pxping,
+                                   ip6_addr_t *src, ip6_addr_t *dst,
+                                   int hopl, int tclass, u16_t icmplen);
+static void pxping_pmgr_icmp6_error(struct pxping *pxping,
+                                    ip6_addr_t *src, ip6_addr_t *dst,
+                                    int hopl, int tclass, u16_t icmplen);
+
+static void pxping_pmgr_forward_inbound(struct pxping *pxping, u16_t iplen);
+static void pxping_pcb_forward_inbound(void *arg);
+
+static void pxping_pmgr_forward_inbound6(struct pxping *pxping,
+                                         ip6_addr_t *src, ip6_addr_t *dst,
+                                         u8_t hopl, u8_t tclass,
+                                         u16_t icmplen);
+static void pxping_pcb_forward_inbound6(void *arg);
+
+/*
+ * NB: This is not documented except in RTFS.
+ *
+ * If ip_output_if() is passed dest == NULL then it treats p as
+ * complete IP packet with payload pointing to the IP header.  It does
+ * not build IP header, ignores all header-related arguments, fetches
+ * real destination from the header in the pbuf and outputs pbuf to
+ * the specified netif.
+ */
+#define ip_raw_output_if(p, netif)                      \
+    (ip_output_if((p), NULL, NULL, 0, 0, 0, (netif)))
+
+
+
+static struct pxping g_pxping;
+
+
+err_t
+pxping_init(struct netif *netif, SOCKET sock4, SOCKET sock6)
+{
+    const int on = 1;
+    int status;
+
+    if (sock4 == INVALID_SOCKET && sock6 == INVALID_SOCKET) {
+        return ERR_VAL;
+    }
+
+    g_pxping.netif = netif;
+    sys_mutex_new(&g_pxping.lock);
+
+    g_pxping.sock4 = sock4;
+    if (g_pxping.sock4 != INVALID_SOCKET) {
+#ifdef DF_WITH_IP_HDRINCL
+        g_pxping.hdrincl = 0;
+#else
+        g_pxping.df = -1;
+#endif
+        g_pxping.ttl = -1;
+        g_pxping.tos = 0;
+
+#ifdef RT_OS_LINUX
+        {
+            const int dont = IP_PMTUDISC_DONT;
+            status = setsockopt(sock4, IPPROTO_IP, IP_MTU_DISCOVER,
+                                &dont, sizeof(dont));
+            if (status != 0) {
+                DPRINTF(("IP_MTU_DISCOVER: %R[sockerr]\n", SOCKERRNO()));
+            }
+        }
+#endif /* RT_OS_LINUX */
+
+        g_pxping.pmhdl4.callback = pxping_pmgr_pump;
+        g_pxping.pmhdl4.data = (void *)&g_pxping;
+        g_pxping.pmhdl4.slot = -1;
+        pollmgr_add(&g_pxping.pmhdl4, g_pxping.sock4, POLLIN);
+
+        ping_proxy_accept(pxping_recv4, &g_pxping);
+    }
+
+    g_pxping.sock6 = sock6;
+#ifdef RT_OS_WINDOWS
+    /* we need recvmsg */
+    if (g_pxping.sock6 != INVALID_SOCKET) {
+        status = pxping_init_windows(&g_pxping);
+        if (status == SOCKET_ERROR) {
+            g_pxping.sock6 = INVALID_SOCKET;
+            /* close(sock6); */
+        }
+    }
+#endif
+    if (g_pxping.sock6 != INVALID_SOCKET) {
+        g_pxping.hopl = -1;
+
+#if !defined(IPV6_RECVPKTINFO)
+#define IPV6_RECVPKTINFO (IPV6_PKTINFO)
+#endif
+        status = setsockopt(sock6, IPPROTO_IPV6, IPV6_RECVPKTINFO,
+                            (const char *)&on, sizeof(on));
+        if (status < 0) {
+            DPRINTF(("IPV6_RECVPKTINFO: %R[sockerr]\n", SOCKERRNO()));
+            /* XXX: for now this is fatal */
+        }
+
+#if !defined(IPV6_RECVHOPLIMIT)
+#define IPV6_RECVHOPLIMIT (IPV6_HOPLIMIT)
+#endif
+        status = setsockopt(sock6, IPPROTO_IPV6, IPV6_RECVHOPLIMIT,
+                            (const char *)&on, sizeof(on));
+        if (status < 0) {
+            DPRINTF(("IPV6_RECVHOPLIMIT: %R[sockerr]\n", SOCKERRNO()));
+        }
+
+#ifdef IPV6_RECVTCLASS  /* new in RFC 3542, there's no RFC 2292 counterpart */
+        /** @todo IPV6_RECVTCLASS */
+#endif
+
+        g_pxping.pmhdl6.callback = pxping_pmgr_pump;
+        g_pxping.pmhdl6.data = (void *)&g_pxping;
+        g_pxping.pmhdl6.slot = -1;
+        pollmgr_add(&g_pxping.pmhdl6, g_pxping.sock6, POLLIN);
+
+        ping6_proxy_accept(pxping_recv6, &g_pxping);
+    }
+
+    status = RTStrFormatTypeRegister("ping_pcb", pxping_pcb_rtstrfmt, NULL);
+    AssertRC(status);
+
+    return ERR_OK;
+}
+
+
+#ifdef RT_OS_WINDOWS
+static int
+pxping_init_windows(struct pxping *pxping)
+{
+    GUID WSARecvMsgGUID = WSAID_WSARECVMSG;
+    DWORD nread;
+    int status;
+
+    pxping->pfWSARecvMsg6 = NULL;
+    status = WSAIoctl(pxping->sock6,
+                      SIO_GET_EXTENSION_FUNCTION_POINTER,
+                      &WSARecvMsgGUID, sizeof(WSARecvMsgGUID),
+                      &pxping->pfWSARecvMsg6, sizeof(pxping->pfWSARecvMsg6),
+                      &nread,
+                      NULL, NULL);
+    return status;
+}
+#endif  /* RT_OS_WINDOWS */
+
+
+static u32_t
+chksum_delta_16(u16_t oval, u16_t nval)
+{
+    u32_t sum = (u16_t)~oval;
+    sum += nval;
+    return sum;
+}
+
+
+static u32_t
+chksum_update_16(u16_t *oldp, u16_t nval)
+{
+    u32_t sum = chksum_delta_16(*oldp, nval);
+    *oldp = nval;
+    return sum;
+}
+
+
+static u32_t
+chksum_delta_32(u32_t oval, u32_t nval)
+{
+    u32_t sum = ~oval;
+    sum = FOLD_U32T(sum);
+    sum += FOLD_U32T(nval);
+    return sum;
+}
+
+
+static u32_t
+chksum_update_32(u32_t *oldp, u32_t nval)
+{
+    u32_t sum = chksum_delta_32(*oldp, nval);
+    *oldp = nval;
+    return sum;
+}
+
+
+static u32_t
+chksum_delta_ipv6(const ip6_addr_t *oldp, const ip6_addr_t *newp)
+{
+    u32_t sum;
+
+    sum  = chksum_delta_32(oldp->addr[0], newp->addr[0]);
+    sum += chksum_delta_32(oldp->addr[1], newp->addr[1]);
+    sum += chksum_delta_32(oldp->addr[2], newp->addr[2]);
+    sum += chksum_delta_32(oldp->addr[3], newp->addr[3]);
+
+    return sum;
+}
+
+
+static u32_t
+chksum_update_ipv6(ip6_addr_t *oldp, const ip6_addr_t *newp)
+{
+    u32_t sum;
+
+    sum  = chksum_update_32(&oldp->addr[0], newp->addr[0]);
+    sum += chksum_update_32(&oldp->addr[1], newp->addr[1]);
+    sum += chksum_update_32(&oldp->addr[2], newp->addr[2]);
+    sum += chksum_update_32(&oldp->addr[3], newp->addr[3]);
+
+    return sum;
+}
+
+
+/**
+ * ICMP Echo Request in pbuf "p" is to be proxied.
+ */
+static void
+pxping_recv4(void *arg, struct pbuf *p)
+{
+    struct pxping *pxping = (struct pxping *)arg;
+    struct ping_pcb *pcb;
+#ifdef DF_WITH_IP_HDRINCL
+    struct ip_hdr iph_orig;
+#endif
+    struct icmp_echo_hdr icmph_orig;
+    struct ip_hdr *iph;
+    struct icmp_echo_hdr *icmph;
+    int df, ttl, tos;
+    u32_t sum;
+    u16_t iphlen;
+    int status;
+
+    iphlen = ip_current_header_tot_len();
+    if (iphlen != IP_HLEN) {    /* we don't do options */
+        pbuf_free(p);
+        return;
+    }
+
+    iph = (/* UNCONST */ struct ip_hdr *)ip_current_header();
+    icmph = (struct icmp_echo_hdr *)p->payload;
+
+    pcb = pxping_pcb_for_request(pxping, 0,
+                                 ipX_current_src_addr(),
+                                 ipX_current_dest_addr(),
+                                 icmph->id);
+    if (pcb == NULL) {
+        pbuf_free(p);
+        return;
+    }
+
+    DPRINTF(("ping %p: %R[ping_pcb] seq %d len %u ttl %d\n",
+             pcb, pcb,
+             ntohs(icmph->seqno), (unsigned int)p->tot_len,
+             IPH_TTL(iph)));
+
+    ttl = IPH_TTL(iph);
+    if (!pcb->is_mapped) {
+        if (RT_UNLIKELY(ttl == 1)) {
+            status = pbuf_header(p, iphlen); /* back to IP header */
+            if (RT_LIKELY(status == 0)) {
+                icmp_time_exceeded(p, ICMP_TE_TTL);
+            }
+            pbuf_free(p);
+            return;
+        }
+        --ttl;
+    }
+
+    /*
+     * OS X doesn't provide a socket option to control fragmentation.
+     * Solaris doesn't provide IP_DONTFRAG on all releases we support.
+     * In this case we have to use IP_HDRINCL.  We don't want to use
+     * it always since it doesn't handle fragmentation (but that's ok
+     * for DF) and Windows doesn't do automatic source address
+     * selection with IP_HDRINCL.
+     */
+    df = (IPH_OFFSET(iph) & PP_HTONS(IP_DF)) != 0;
+
+#ifdef DF_WITH_IP_HDRINCL
+    if (df != pxping->hdrincl) {
+        status = setsockopt(pxping->sock4, IPPROTO_IP, IP_HDRINCL,
+                            &df, sizeof(df));
+        if (RT_LIKELY(status == 0)) {
+            pxping->hdrincl = df;
+        }
+        else {
+            DPRINTF(("IP_HDRINCL: %R[sockerr]\n", SOCKERRNO()));
+        }
+    }
+
+    if (pxping->hdrincl) {
+        status = pbuf_header(p, iphlen); /* back to IP header */
+        if (RT_UNLIKELY(status != 0)) {
+            pbuf_free(p);
+            return;
+        }
+
+        /* we will overwrite IP header, save original for ICMP errors */
+        memcpy(&iph_orig, iph, iphlen);
+
+        if (pcb->is_mapped) {
+            ip4_addr_set_u32(&iph->dest, pcb->peer.sin.sin_addr.s_addr);
+        }
+
+        if (g_proxy_options->src4 != NULL) {
+            ip4_addr_set_u32(&iph->src, g_proxy_options->src4->sin_addr.s_addr);
+        }
+        else {
+            /* let the kernel select suitable source address */
+            ip_addr_set_any(&iph->src);
+        }
+
+        IPH_TTL_SET(iph, ttl);  /* already decremented */
+        IPH_ID_SET(iph, 0);     /* kernel will set one */
+#ifdef RT_OS_DARWIN
+        /* wants ip_offset and ip_len fields in host order */
+        IPH_OFFSET_SET(iph, ntohs(IPH_OFFSET(iph)));
+        IPH_LEN_SET(iph, ntohs(IPH_LEN(iph)));
+        /* wants checksum of everything (sic!), in host order */
+        sum = inet_chksum_pbuf(p);
+        IPH_CHKSUM_SET(iph, sum);
+#else /* !RT_OS_DARWIN  */
+        IPH_CHKSUM_SET(iph, 0); /* kernel will recalculate */
+#endif
+    }
+    else /* !pxping->hdrincl */
+#endif   /* DF_WITH_IP_HDRINCL */
+    {
+#if !defined(DF_WITH_IP_HDRINCL)
+        /* control DF flag via setsockopt(2) */
+#define USE_DF_OPTION(_Optname)                         \
+        const int dfopt = _Optname;                     \
+        const char * const dfoptname = #_Optname; NOREF(dfoptname)
+#if   defined(RT_OS_LINUX)
+        USE_DF_OPTION(IP_MTU_DISCOVER);
+        df = df ? IP_PMTUDISC_DO : IP_PMTUDISC_DONT;
+#elif defined(RT_OS_SOLARIS) || defined(RT_OS_FREEBSD)
+        USE_DF_OPTION(IP_DONTFRAG);
+#elif defined(RT_OS_WINDOWS)
+        USE_DF_OPTION(IP_DONTFRAGMENT);
+#endif
+        if (df != pxping->df) {
+            status = setsockopt(pxping->sock4, IPPROTO_IP, dfopt,
+                                (char *)&df, sizeof(df));
+            if (RT_LIKELY(status == 0)) {
+                pxping->df = df;
+            }
+            else {
+                DPRINTF(("%s: %R[sockerr]\n", dfoptname, SOCKERRNO()));
+            }
+        }
+#endif /* !DF_WITH_IP_HDRINCL */
+
+        if (ttl != pxping->ttl) {
+            status = setsockopt(pxping->sock4, IPPROTO_IP, IP_TTL,
+                                (char *)&ttl, sizeof(ttl));
+            if (RT_LIKELY(status == 0)) {
+                pxping->ttl = ttl;
+            }
+            else {
+                DPRINTF(("IP_TTL: %R[sockerr]\n", SOCKERRNO()));
+            }
+        }
+
+        tos = IPH_TOS(iph);
+        if (tos != pxping->tos) {
+            status = setsockopt(pxping->sock4, IPPROTO_IP, IP_TOS,
+                                (char *)&tos, sizeof(tos));
+            if (RT_LIKELY(status == 0)) {
+                pxping->tos = tos;
+            }
+            else {
+                DPRINTF(("IP_TOS: %R[sockerr]\n", SOCKERRNO()));
+            }
+        }
+    }
+
+    /* rewrite ICMP echo header */
+    memcpy(&icmph_orig, icmph, sizeof(*icmph));
+    sum = (u16_t)~icmph->chksum;
+    sum += chksum_update_16(&icmph->id, pcb->host_id);
+    sum = FOLD_U32T(sum);
+    icmph->chksum = ~sum;
+
+    status = proxy_sendto(pxping->sock4, p,
+                          &pcb->peer.sin, sizeof(pcb->peer.sin));
+    if (status != 0) {
+        int error = -status;
+        DPRINTF(("%s: sendto: %R[sockerr]\n", __func__, error));
+
+#ifdef DF_WITH_IP_HDRINCL
+        if (pxping->hdrincl) {
+            /* restore original IP header */
+            memcpy(iph, &iph_orig, iphlen);
+        }
+        else
+#endif
+        {
+            status = pbuf_header(p, iphlen); /* back to IP header */
+            if (RT_UNLIKELY(status != 0)) {
+                pbuf_free(p);
+                return;
+            }
+        }
+
+        /* restore original ICMP header */
+        memcpy(icmph, &icmph_orig, sizeof(*icmph));
+
+        /*
+         * Some ICMP errors may be generated by the kernel and we read
+         * them from the socket and forward them normally, hence the
+         * ifdefs below.
+         */
+        switch (error) {
+
+#if !( defined(RT_OS_SOLARIS)                                   \
+    || (defined(RT_OS_LINUX) && !defined(DF_WITH_IP_HDRINCL))   \
+    )
+        case EMSGSIZE:
+            icmp_dest_unreach(p, ICMP_DUR_FRAG);
+            break;
+#endif
+
+        case ENETDOWN:
+        case ENETUNREACH:
+            icmp_dest_unreach(p, ICMP_DUR_NET);
+            break;
+
+        case EHOSTDOWN:
+        case EHOSTUNREACH:
+            icmp_dest_unreach(p, ICMP_DUR_HOST);
+            break;
+        }
+    }
+
+    pbuf_free(p);
+}
+
+
+/**
+ * ICMPv6 Echo Request in pbuf "p" is to be proxied.
+ */
+static void
+pxping_recv6(void *arg, struct pbuf *p)
+{
+    struct pxping *pxping = (struct pxping *)arg;
+    struct ping_pcb *pcb;
+    struct ip6_hdr *iph;
+    struct icmp6_echo_hdr *icmph;
+    int hopl;
+    u16_t iphlen;
+    u16_t id, seq;
+    int status;
+
+    iph = (/* UNCONST */ struct ip6_hdr *)ip6_current_header();
+    iphlen = ip_current_header_tot_len();
+
+    icmph = (struct icmp6_echo_hdr *)p->payload;
+
+    id  = icmph->id;
+    seq = icmph->seqno;
+
+    pcb = pxping_pcb_for_request(pxping, 1,
+                                 ipX_current_src_addr(),
+                                 ipX_current_dest_addr(),
+                                 id);
+    if (pcb == NULL) {
+        pbuf_free(p);
+        return;
+    }
+
+    DPRINTF(("ping %p: %R[ping_pcb] seq %d len %u hopl %d\n",
+             pcb, pcb,
+             ntohs(seq), (unsigned int)p->tot_len,
+             IP6H_HOPLIM(iph)));
+
+    hopl = IP6H_HOPLIM(iph);
+    if (!pcb->is_mapped) {
+        if (hopl == 1) {
+            status = pbuf_header(p, iphlen); /* back to IP header */
+            if (RT_LIKELY(status == 0)) {
+                icmp6_time_exceeded(p, ICMP6_TE_HL);
+            }
+            pbuf_free(p);
+            return;
+        }
+        --hopl;
+    }
+
+    /*
+     * Rewrite ICMPv6 echo header.  We don't need to recompute the
+     * checksum since, unlike IPv4, checksum includes pseudo-header.
+     * OS computes checksum for us on send() since it needs to select
+     * source address.
+     */
+    icmph->id = pcb->host_id;
+
+    /** @todo use control messages to save a syscall? */
+    if (hopl != pxping->hopl) {
+        status = setsockopt(pxping->sock6, IPPROTO_IPV6, IPV6_UNICAST_HOPS,
+                            (char *)&hopl, sizeof(hopl));
+        if (status == 0) {
+            pxping->hopl = hopl;
+        }
+        else {
+            DPRINTF(("IPV6_HOPLIMIT: %R[sockerr]\n", SOCKERRNO()));
+        }
+    }
+
+    status = proxy_sendto(pxping->sock6, p,
+                          &pcb->peer.sin6, sizeof(pcb->peer.sin6));
+    if (status != 0) {
+        int error = -status;
+        DPRINTF(("%s: sendto: %R[sockerr]\n", __func__, error));
+
+        status = pbuf_header(p, iphlen); /* back to IP header */
+        if (RT_UNLIKELY(status != 0)) {
+            pbuf_free(p);
+            return;
+        }
+
+        /* restore original ICMP header */
+        icmph->id = pcb->guest_id;
+
+        switch (error) {
+        case EACCES:
+            icmp6_dest_unreach(p, ICMP6_DUR_PROHIBITED);
+            break;
+
+#ifdef ENONET
+        case ENONET:
+#endif
+        case ENETDOWN:
+        case ENETUNREACH:
+        case EHOSTDOWN:
+        case EHOSTUNREACH:
+            icmp6_dest_unreach(p, ICMP6_DUR_NO_ROUTE);
+            break;
+        }
+    }
+
+    pbuf_free(p);
+}
+
+
+/**
+ * Formatter for %R[ping_pcb].
+ */
+static DECLCALLBACK(size_t)
+pxping_pcb_rtstrfmt(PFNRTSTROUTPUT pfnOutput, void *pvArgOutput,
+                    const char *pszType, const void *pvValue,
+                    int cchWidth, int cchPrecision, unsigned int fFlags,
+                    void *pvUser)
+{
+    const struct ping_pcb *pcb = (const struct ping_pcb *)pvValue;
+    size_t cb = 0;
+
+    NOREF(cchWidth);
+    NOREF(cchPrecision);
+    NOREF(fFlags);
+    NOREF(pvUser);
+
+    AssertReturn(strcmp(pszType, "ping_pcb") == 0, 0);
+
+    if (pcb == NULL) {
+        return RTStrFormat(pfnOutput, pvArgOutput, NULL, NULL, "(null)");
+    }
+
+    /* XXX: %RTnaipv4 takes the value, but %RTnaipv6 takes the pointer */
+    if (pcb->is_ipv6) {
+        cb += RTStrFormat(pfnOutput, pvArgOutput, NULL, NULL,
+                          "%RTnaipv6 -> %RTnaipv6", &pcb->src, &pcb->dst);
+        if (pcb->is_mapped) {
+            cb += RTStrFormat(pfnOutput, pvArgOutput, NULL, NULL,
+                              " (%RTnaipv6)", &pcb->peer.sin6.sin6_addr);
+        }
+    }
+    else {
+        cb += RTStrFormat(pfnOutput, pvArgOutput, NULL, NULL,
+                          "%RTnaipv4 -> %RTnaipv4",
+                          ip4_addr_get_u32(ipX_2_ip(&pcb->src)),
+                          ip4_addr_get_u32(ipX_2_ip(&pcb->dst)));
+        if (pcb->is_mapped) {
+            cb += RTStrFormat(pfnOutput, pvArgOutput, NULL, NULL,
+                              " (%RTnaipv4)", pcb->peer.sin.sin_addr.s_addr);
+        }
+    }
+
+    cb += RTStrFormat(pfnOutput, pvArgOutput, NULL, NULL,
+                      " id %04x->%04x", ntohs(pcb->guest_id), ntohs(pcb->host_id));
+
+    return cb;
+}
+
+
+static struct ping_pcb *
+pxping_pcb_allocate(struct pxping *pxping)
+{
+    struct ping_pcb *pcb;
+
+    if (pxping->npcbs >= PXPING_MAX_PCBS) {
+        return NULL;
+    }
+
+    pcb = (struct ping_pcb *)malloc(sizeof(*pcb));
+    if (pcb == NULL) {
+        return NULL;
+    }
+
+    ++pxping->npcbs;
+    return pcb;
+}
+
+
+static void
+pxping_pcb_delete(struct pxping *pxping, struct ping_pcb *pcb)
+{
+    LWIP_ASSERT1(pxping->npcbs > 0);
+    LWIP_ASSERT1(pcb->next == NULL);
+    LWIP_ASSERT1(pcb->pprev_timeout == NULL);
+
+    DPRINTF(("%s: ping %p\n", __func__, (void *)pcb));
+
+    --pxping->npcbs;
+    free(pcb);
+}
+
+
+static void
+pxping_timeout_add(struct pxping *pxping, struct ping_pcb *pcb)
+{
+    struct ping_pcb **chain;
+
+    LWIP_ASSERT1(pcb->pprev_timeout == NULL);
+
+    chain = &pxping->timeout_list[pcb->timeout_slot];
+    if ((pcb->next_timeout = *chain) != NULL) {
+        (*chain)->pprev_timeout = &pcb->next_timeout;
+    }
+    *chain = pcb;
+    pcb->pprev_timeout = chain;
+}
+
+
+static void
+pxping_timeout_del(struct pxping *pxping, struct ping_pcb *pcb)
+{
+    LWIP_UNUSED_ARG(pxping);
+
+    LWIP_ASSERT1(pcb->pprev_timeout != NULL);
+    if (pcb->next_timeout != NULL) {
+        pcb->next_timeout->pprev_timeout = pcb->pprev_timeout;
+    }
+    *pcb->pprev_timeout = pcb->next_timeout;
+    pcb->pprev_timeout = NULL;
+    pcb->next_timeout = NULL;
+}
+
+
+static void
+pxping_pcb_register(struct pxping *pxping, struct ping_pcb *pcb)
+{
+    pcb->next = pxping->pcbs;
+    pxping->pcbs = pcb;
+
+    pxping_timeout_add(pxping, pcb);
+}
+
+
+static void
+pxping_pcb_deregister(struct pxping *pxping, struct ping_pcb *pcb)
+{
+    struct ping_pcb **p;
+
+    for (p = &pxping->pcbs; *p != NULL; p = &(*p)->next) {
+        if (*p == pcb) {
+            *p = pcb->next;
+            pcb->next = NULL;
+            break;
+        }
+    }
+
+    pxping_timeout_del(pxping, pcb);
+}
+
+
+static struct ping_pcb *
+pxping_pcb_for_request(struct pxping *pxping,
+                       int is_ipv6, ipX_addr_t *src, ipX_addr_t *dst,
+                       u16_t guest_id)
+{
+    struct ping_pcb *pcb;
+
+    /* on lwip thread, so no concurrent updates */
+    for (pcb = pxping->pcbs; pcb != NULL; pcb = pcb->next) {
+        if (pcb->guest_id == guest_id
+            && pcb->is_ipv6 == is_ipv6
+            && ipX_addr_cmp(is_ipv6, &pcb->dst, dst)
+            && ipX_addr_cmp(is_ipv6, &pcb->src, src))
+        {
+            break;
+        }
+    }
+
+    if (pcb == NULL) {
+        int mapped;
+
+        pcb = pxping_pcb_allocate(pxping);
+        if (pcb == NULL) {
+            return NULL;
+        }
+
+        pcb->is_ipv6 = is_ipv6;
+        ipX_addr_copy(is_ipv6, pcb->src, *src);
+        ipX_addr_copy(is_ipv6, pcb->dst, *dst);
+
+        pcb->guest_id = guest_id;
+#ifdef RT_OS_WINDOWS
+# define random() (rand())
+#endif
+        pcb->host_id = random() & 0xffffUL;
+
+        pcb->pprev_timeout = NULL;
+        pcb->next_timeout = NULL;
+
+        if (is_ipv6) {
+            pcb->peer.sin6.sin6_family = AF_INET6;
+#if HAVE_SA_LEN
+            pcb->peer.sin6.sin6_len = sizeof(pcb->peer.sin6);
+#endif
+            pcb->peer.sin6.sin6_port = htons(IPPROTO_ICMPV6);
+            pcb->peer.sin6.sin6_flowinfo = 0;
+            mapped = pxremap_outbound_ip6((ip6_addr_t *)&pcb->peer.sin6.sin6_addr,
+                                          ipX_2_ip6(&pcb->dst));
+        }
+        else {
+            pcb->peer.sin.sin_family = AF_INET;
+#if HAVE_SA_LEN
+            pcb->peer.sin.sin_len = sizeof(pcb->peer.sin);
+#endif
+            pcb->peer.sin.sin_port = htons(IPPROTO_ICMP);
+            mapped = pxremap_outbound_ip4((ip_addr_t *)&pcb->peer.sin.sin_addr,
+                                          ipX_2_ip(&pcb->dst));
+        }
+
+        if (mapped == PXREMAP_FAILED) {
+            free(pcb);
+            return NULL;
+        }
+        else {
+            pcb->is_mapped = (mapped == PXREMAP_MAPPED);
+        }
+
+        pcb->timeout_slot = pxping->timeout_slot;
+
+        sys_mutex_lock(&pxping->lock);
+        pxping_pcb_register(pxping, pcb);
+        sys_mutex_unlock(&pxping->lock);
+
+        DPRINTF(("ping %p: %R[ping_pcb] - created\n", pcb, pcb));
+
+        pxping_timer_needed(pxping);
+    }
+    else {
+        /* just bump up expiration timeout lazily */
+        DPRINTF(("ping %p: %R[ping_pcb] - slot %d -> %d\n",
+                 pcb, pcb,
+                 (unsigned int)pcb->timeout_slot,
+                 (unsigned int)pxping->timeout_slot));
+        pcb->timeout_slot = pxping->timeout_slot;
+    }
+
+    return pcb;
+}
+
+
+/* GCC 12.2.1 complains that array subscript is partly outside
+ * of array bounds in expansion of ipX_addr_cmp. */
+#if RT_GNUC_PREREQ(12, 0)
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Warray-bounds"
+#endif
+/**
+ * Called on pollmgr thread.  Caller must do the locking since caller
+ * is going to use the returned pcb, which needs to be protected from
+ * being expired by pxping_timer() on lwip thread.
+ */
+static struct ping_pcb *
+pxping_pcb_for_reply(struct pxping *pxping,
+                     int is_ipv6, ipX_addr_t *dst, u16_t host_id)
+{
+    struct ping_pcb *pcb;
+
+    for (pcb = pxping->pcbs; pcb != NULL; pcb = pcb->next) {
+        if (pcb->host_id == host_id
+            && pcb->is_ipv6 == is_ipv6
+            /* XXX: allow broadcast pings? */
+            && ipX_addr_cmp(is_ipv6, &pcb->dst, dst))
+        {
+            return pcb;
+        }
+    }
+
+    return NULL;
+}
+#if RT_GNUC_PREREQ(12, 0)
+# pragma GCC diagnostic pop
+#endif
+
+
+static void
+pxping_timer(void *arg)
+{
+    struct pxping *pxping = (struct pxping *)arg;
+    struct ping_pcb **chain, *pcb;
+
+    pxping->timer_active = 0;
+
+    /*
+     * New slot points to the list of pcbs to check for expiration.
+     */
+    LWIP_ASSERT1(pxping->timeout_slot < TIMEOUT);
+    if (++pxping->timeout_slot == TIMEOUT) {
+        pxping->timeout_slot = 0;
+    }
+
+    chain = &pxping->timeout_list[pxping->timeout_slot];
+    pcb = *chain;
+
+    /* protect from pollmgr concurrent reads */
+    sys_mutex_lock(&pxping->lock);
+
+    while (pcb != NULL) {
+        struct ping_pcb *xpcb = pcb;
+        pcb = pcb->next_timeout;
+
+        if (xpcb->timeout_slot == pxping->timeout_slot) {
+            /* expired */
+            pxping_pcb_deregister(pxping, xpcb);
+            pxping_pcb_delete(pxping, xpcb);
+        }
+        else {
+            /*
+             * If there was another request, we updated timeout_slot
+             * but delayed actually moving the pcb until now.
+             */
+            pxping_timeout_del(pxping, xpcb); /* from current slot */
+            pxping_timeout_add(pxping, xpcb); /* to new slot */
+        }
+    }
+
+    sys_mutex_unlock(&pxping->lock);
+    pxping_timer_needed(pxping);
+}
+
+
+static void
+pxping_timer_needed(struct pxping *pxping)
+{
+    if (!pxping->timer_active && pxping->pcbs != NULL) {
+        pxping->timer_active = 1;
+        sys_timeout(1 * 1000, pxping_timer, pxping);
+    }
+}
+
+
+static int
+pxping_pmgr_pump(struct pollmgr_handler *handler, SOCKET fd, int revents)
+{
+    struct pxping *pxping;
+
+    pxping = (struct pxping *)handler->data;
+    LWIP_ASSERT1(fd == pxping->sock4 || fd == pxping->sock6);
+
+    if (revents & ~(POLLIN|POLLERR)) {
+        DPRINTF0(("%s: unexpected revents 0x%x\n", __func__, revents));
+        return POLLIN;
+    }
+
+    if (revents & POLLERR) {
+        int sockerr = -1;
+        socklen_t optlen = (socklen_t)sizeof(sockerr);
+        int status;
+
+        status = getsockopt(fd, SOL_SOCKET,
+                            SO_ERROR, (char *)&sockerr, &optlen);
+        if (status < 0) {
+            DPRINTF(("%s: sock %d: SO_ERROR failed: %R[sockerr]\n",
+                     __func__, fd, SOCKERRNO()));
+        }
+        else {
+            DPRINTF(("%s: sock %d: %R[sockerr]\n",
+                     __func__, fd, sockerr));
+        }
+    }
+
+    if ((revents & POLLIN) == 0) {
+        return POLLIN;
+    }
+
+    if (fd == pxping->sock4) {
+        pxping_pmgr_icmp4(pxping);
+    }
+    else /* fd == pxping->sock6 */ {
+        pxping_pmgr_icmp6(pxping);
+    }
+
+    return POLLIN;
+}
+
+
+/**
+ * Process incoming ICMP message for the host.
+ * NB: we will get a lot of spam here and have to sift through it.
+ */
+static void
+pxping_pmgr_icmp4(struct pxping *pxping)
+{
+    struct sockaddr_in sin;
+    socklen_t salen = sizeof(sin);
+    ssize_t nread;
+    struct ip_hdr *iph;
+    struct icmp_echo_hdr *icmph;
+    u16_t iplen, ipoff;
+
+    memset(&sin, 0, sizeof(sin));
+
+    /*
+     * Reads from raw IPv4 sockets deliver complete IP datagrams with
+     * IP header included.
+     */
+    nread = recvfrom(pxping->sock4, pollmgr_udpbuf, sizeof(pollmgr_udpbuf), 0,
+                     (struct sockaddr *)&sin, &salen);
+    if (nread < 0) {
+        DPRINTF(("%s: %R[sockerr]\n", __func__, SOCKERRNO()));
+        return;
+    }
+
+    if (nread < IP_HLEN) {
+        DPRINTF2(("%s: read %d bytes, IP header truncated\n",
+                  __func__, (unsigned int)nread));
+        return;
+    }
+
+    iph = (struct ip_hdr *)pollmgr_udpbuf;
+
+    /* match version */
+    if (IPH_V(iph) != 4) {
+        DPRINTF2(("%s: unexpected IP version %d\n", __func__, IPH_V(iph)));
+        return;
+    }
+
+    /* no fragmentation */
+    ipoff = IPH_OFFSET(iph);
+#if defined(RT_OS_DARWIN)
+    /* darwin reports IPH_OFFSET in host byte order */
+    ipoff = htons(ipoff);
+    IPH_OFFSET_SET(iph, ipoff);
+#endif
+    if ((ipoff & PP_HTONS(IP_OFFMASK | IP_MF)) != 0) {
+        DPRINTF2(("%s: dropping fragmented datagram (0x%04x)\n",
+                  __func__, ntohs(ipoff)));
+        return;
+    }
+
+    /* no options */
+    if (IPH_HL(iph) * 4 != IP_HLEN) {
+        DPRINTF2(("%s: dropping datagram with options (IP header length %d)\n",
+                  __func__, IPH_HL(iph) * 4));
+        return;
+    }
+
+    if (IPH_PROTO(iph) != IP_PROTO_ICMP) {
+        DPRINTF2(("%s: unexpected protocol %d\n", __func__, IPH_PROTO(iph)));
+        return;
+    }
+
+    iplen = IPH_LEN(iph);
+#if !defined(RT_OS_DARWIN)
+    /* darwin reports IPH_LEN in host byte order */
+    iplen = ntohs(iplen);
+#endif
+#if defined(RT_OS_DARWIN) || defined(RT_OS_SOLARIS)
+    /* darwin and solaris change IPH_LEN to payload length only */
+    iplen += IP_HLEN;           /* we verified there are no options */
+    IPH_LEN_SET(iph, htons(iplen));
+#endif
+    if (nread < iplen) {
+        DPRINTF2(("%s: read %d bytes but total length is %d bytes\n",
+                  __func__, (unsigned int)nread, (unsigned int)iplen));
+        return;
+    }
+
+    if (iplen < IP_HLEN + ICMP_HLEN) {
+        DPRINTF2(("%s: IP length %d bytes, ICMP header truncated\n",
+                  __func__, iplen));
+        return;
+    }
+
+    icmph = (struct icmp_echo_hdr *)(pollmgr_udpbuf + IP_HLEN);
+    if (ICMPH_TYPE(icmph) == ICMP_ER) {
+        pxping_pmgr_icmp4_echo(pxping, iplen, &sin);
+    }
+    else if (ICMPH_TYPE(icmph) == ICMP_DUR || ICMPH_TYPE(icmph) == ICMP_TE) {
+        pxping_pmgr_icmp4_error(pxping, iplen, &sin);
+    }
+#if 1
+    else {
+        DPRINTF2(("%s: ignoring ICMP type %d\n", __func__, ICMPH_TYPE(icmph)));
+    }
+#endif
+}
+
+
+/**
+ * Check if this incoming ICMP echo reply is for one of our pings and
+ * forward it to the guest.
+ */
+static void
+pxping_pmgr_icmp4_echo(struct pxping *pxping,
+                       u16_t iplen, struct sockaddr_in *peer)
+{
+    struct ip_hdr *iph;
+    struct icmp_echo_hdr *icmph;
+    u16_t id, seq;
+    ip_addr_t guest_ip, target_ip;
+    int mapped;
+    struct ping_pcb *pcb;
+    u16_t guest_id;
+    u16_t oipsum;
+    u32_t sum;
+    RT_NOREF(peer);
+
+    iph = (struct ip_hdr *)pollmgr_udpbuf;
+    icmph = (struct icmp_echo_hdr *)(pollmgr_udpbuf + IP_HLEN);
+
+    id  = icmph->id;
+    seq = icmph->seqno;
+
+    DPRINTF(("<--- PING %RTnaipv4 id 0x%x seq %d\n",
+             peer->sin_addr.s_addr, ntohs(id), ntohs(seq)));
+
+    /*
+     * Is this a reply to one of our pings?
+     */
+
+    ip_addr_copy(target_ip, iph->src);
+    mapped = pxremap_inbound_ip4(&target_ip, &target_ip);
+    if (mapped == PXREMAP_FAILED) {
+        return;
+    }
+    if (mapped == PXREMAP_ASIS && IPH_TTL(iph) == 1) {
+        DPRINTF2(("%s: dropping packet with ttl 1\n", __func__));
+        return;
+    }
+
+    sys_mutex_lock(&pxping->lock);
+    pcb = pxping_pcb_for_reply(pxping, 0, ip_2_ipX(&target_ip), id);
+    if (pcb == NULL) {
+        sys_mutex_unlock(&pxping->lock);
+        DPRINTF2(("%s: no match\n", __func__));
+        return;
+    }
+
+    DPRINTF2(("%s: pcb %p\n", __func__, (void *)pcb));
+
+    /* save info before unlocking since pcb may expire */
+    ip_addr_copy(guest_ip, *ipX_2_ip(&pcb->src));
+    guest_id = pcb->guest_id;
+
+    sys_mutex_unlock(&pxping->lock);
+
+
+    /*
+     * Rewrite headers and forward to guest.
+     */
+
+    /* rewrite ICMP echo header */
+    sum = (u16_t)~icmph->chksum;
+    sum += chksum_update_16(&icmph->id, guest_id);
+    sum = FOLD_U32T(sum);
+    icmph->chksum = ~sum;
+
+    /* rewrite IP header */
+    oipsum = IPH_CHKSUM(iph);
+    if (oipsum == 0) {
+        /* Solaris doesn't compute checksum for local replies */
+        ip_addr_copy(iph->dest, guest_ip);
+        if (mapped == PXREMAP_MAPPED) {
+            ip_addr_copy(iph->src, target_ip);
+        }
+        else {
+            IPH_TTL_SET(iph, IPH_TTL(iph) - 1);
+        }
+        IPH_CHKSUM_SET(iph, inet_chksum(iph, ntohs(IPH_LEN(iph))));
+    }
+    else {
+        sum = (u16_t)~oipsum;
+        sum += chksum_update_32((u32_t *)&iph->dest,
+                                ip4_addr_get_u32(&guest_ip));
+        if (mapped == PXREMAP_MAPPED) {
+            sum += chksum_update_32((u32_t *)&iph->src,
+                                    ip4_addr_get_u32(&target_ip));
+        }
+        else {
+            IPH_TTL_SET(iph, IPH_TTL(iph) - 1);
+            sum += PP_NTOHS(~0x0100);
+        }
+        sum = FOLD_U32T(sum);
+        IPH_CHKSUM_SET(iph, ~sum);
+    }
+
+    pxping_pmgr_forward_inbound(pxping, iplen);
+}
+
+
+/**
+ * Check if this incoming ICMP error (destination unreachable or time
+ * exceeded) is about one of our pings and forward it to the guest.
+ */
+static void
+pxping_pmgr_icmp4_error(struct pxping *pxping,
+                        u16_t iplen, struct sockaddr_in *peer)
+{
+    struct ip_hdr *iph, *oiph;
+    struct icmp_echo_hdr *icmph, *oicmph;
+    u16_t oipoff, oiphlen, oiplen;
+    u16_t id, seq;
+    ip_addr_t guest_ip, target_ip, error_ip;
+    int target_mapped, error_mapped;
+    struct ping_pcb *pcb;
+    u16_t guest_id;
+    u32_t sum;
+    RT_NOREF(peer);
+
+    iph = (struct ip_hdr *)pollmgr_udpbuf;
+    icmph = (struct icmp_echo_hdr *)(pollmgr_udpbuf + IP_HLEN);
+
+    /*
+     * Inner IP datagram is not checked by the kernel and may be
+     * anything, possibly malicious.
+     */
+
+    oipoff = IP_HLEN + ICMP_HLEN;
+    oiplen = iplen - oipoff; /* NB: truncated length, not IPH_LEN(oiph) */
+    if (oiplen < IP_HLEN) {
+        DPRINTF2(("%s: original datagram truncated to %d bytes\n",
+                  __func__, oiplen));
+    }
+
+    /* IP header of the original message */
+    oiph = (struct ip_hdr *)(pollmgr_udpbuf + oipoff);
+
+    /* match version */
+    if (IPH_V(oiph) != 4) {
+        DPRINTF2(("%s: unexpected IP version %d\n", __func__, IPH_V(oiph)));
+        return;
+    }
+
+    /* can't match fragments except the first one */
+    if ((IPH_OFFSET(oiph) & PP_HTONS(IP_OFFMASK)) != 0) {
+        DPRINTF2(("%s: ignoring fragment with offset %d\n",
+                  __func__, ntohs(IPH_OFFSET(oiph) & PP_HTONS(IP_OFFMASK))));
+        return;
+    }
+
+    if (IPH_PROTO(oiph) != IP_PROTO_ICMP) {
+#if 0
+        /* don't spam with every "destination unreachable" in the system */
+        DPRINTF2(("%s: ignoring protocol %d\n", __func__, IPH_PROTO(oiph)));
+#endif
+        return;
+    }
+
+    oiphlen = IPH_HL(oiph) * 4;
+    if (oiplen < oiphlen + ICMP_HLEN) {
+        DPRINTF2(("%s: original datagram truncated to %d bytes\n",
+                  __func__, oiplen));
+        return;
+    }
+
+    oicmph = (struct icmp_echo_hdr *)(pollmgr_udpbuf + oipoff + oiphlen);
+    if (ICMPH_TYPE(oicmph) != ICMP_ECHO) {
+        DPRINTF2(("%s: ignoring ICMP error for original ICMP type %d\n",
+                  __func__, ICMPH_TYPE(oicmph)));
+        return;
+    }
+
+    id  = oicmph->id;
+    seq = oicmph->seqno;
+
+    DPRINTF2(("%s: ping %RTnaipv4 id 0x%x seq %d",
+              __func__, ip4_addr_get_u32(&oiph->dest), ntohs(id), ntohs(seq)));
+    if (ICMPH_TYPE(icmph) == ICMP_DUR) {
+        DPRINTF2((" unreachable (code %d)\n", ICMPH_CODE(icmph)));
+    }
+    else {
+        DPRINTF2((" time exceeded\n"));
+    }
+
+
+    /*
+     * Is the inner (failed) datagram one of our pings?
+     */
+
+    ip_addr_copy(target_ip, oiph->dest); /* inner (failed) */
+    target_mapped = pxremap_inbound_ip4(&target_ip, &target_ip);
+    if (target_mapped == PXREMAP_FAILED) {
+        return;
+    }
+
+    sys_mutex_lock(&pxping->lock);
+    pcb = pxping_pcb_for_reply(pxping, 0, ip_2_ipX(&target_ip), id);
+    if (pcb == NULL) {
+        sys_mutex_unlock(&pxping->lock);
+        DPRINTF2(("%s: no match\n", __func__));
+        return;
+    }
+
+    DPRINTF2(("%s: pcb %p\n", __func__, (void *)pcb));
+
+    /* save info before unlocking since pcb may expire */
+    ip_addr_copy(guest_ip, *ipX_2_ip(&pcb->src));
+    guest_id = pcb->guest_id;
+
+    sys_mutex_unlock(&pxping->lock);
+
+
+    /*
+     * Rewrite both inner and outer headers and forward to guest.
+     * Note that the checksum of the outer ICMP error message is
+     * preserved by the changes we do to inner headers.
+     */
+
+    ip_addr_copy(error_ip, iph->src); /* node that reports the error */
+    error_mapped = pxremap_inbound_ip4(&error_ip, &error_ip);
+    if (error_mapped == PXREMAP_FAILED) {
+        return;
+    }
+    if (error_mapped == PXREMAP_ASIS && IPH_TTL(iph) == 1) {
+        DPRINTF2(("%s: dropping packet with ttl 1\n", __func__));
+        return;
+    }
+
+    /* rewrite inner ICMP echo header */
+    sum = (u16_t)~oicmph->chksum;
+    sum += chksum_update_16(&oicmph->id, guest_id);
+    sum = FOLD_U32T(sum);
+    oicmph->chksum = ~sum;
+
+    /* rewrite inner IP header */
+#if defined(RT_OS_DARWIN)
+    /* darwin converts inner length to host byte order too */
+    IPH_LEN_SET(oiph, htons(IPH_LEN(oiph)));
+#endif
+    sum = (u16_t)~IPH_CHKSUM(oiph);
+    sum += chksum_update_32((u32_t *)&oiph->src, ip4_addr_get_u32(&guest_ip));
+    if (target_mapped == PXREMAP_MAPPED) {
+        sum += chksum_update_32((u32_t *)&oiph->dest, ip4_addr_get_u32(&target_ip));
+    }
+    sum = FOLD_U32T(sum);
+    IPH_CHKSUM_SET(oiph, ~sum);
+
+    /* rewrite outer IP header */
+    sum = (u16_t)~IPH_CHKSUM(iph);
+    sum += chksum_update_32((u32_t *)&iph->dest, ip4_addr_get_u32(&guest_ip));
+    if (error_mapped == PXREMAP_MAPPED) {
+        sum += chksum_update_32((u32_t *)&iph->src, ip4_addr_get_u32(&error_ip));
+    }
+    else {
+        IPH_TTL_SET(iph, IPH_TTL(iph) - 1);
+        sum += PP_NTOHS(~0x0100);
+    }
+    sum = FOLD_U32T(sum);
+    IPH_CHKSUM_SET(iph, ~sum);
+
+    pxping_pmgr_forward_inbound(pxping, iplen);
+}
+
+
+/**
+ * Process incoming ICMPv6 message for the host.
+ * NB: we will get a lot of spam here and have to sift through it.
+ */
+static void
+pxping_pmgr_icmp6(struct pxping *pxping)
+{
+#ifndef RT_OS_WINDOWS
+    struct msghdr mh;
+    ssize_t nread;
+#else
+    WSAMSG mh;
+    DWORD nread;
+#endif
+    IOVEC iov[1];
+    static u8_t cmsgbuf[128];
+    struct cmsghdr *cmh;
+    struct sockaddr_in6 sin6;
+    /* socklen_t salen = sizeof(sin6); - unused */
+    struct icmp6_echo_hdr *icmph;
+    struct in6_pktinfo *pktinfo;
+    int hopl, tclass;
+#ifdef RT_OS_WINDOWS
+    int status;
+#endif
+
+    /*
+     * Reads from raw IPv6 sockets deliver only the payload.  Full
+     * headers are available via recvmsg(2)/cmsg(3).
+     */
+    IOVEC_SET_BASE(iov[0], pollmgr_udpbuf);
+    IOVEC_SET_LEN(iov[0], sizeof(pollmgr_udpbuf));
+
+    memset(&mh, 0, sizeof(mh));
+#ifndef RT_OS_WINDOWS
+    mh.msg_name = &sin6;
+    mh.msg_namelen = sizeof(sin6);
+    mh.msg_iov = iov;
+    mh.msg_iovlen = 1;
+    mh.msg_control = cmsgbuf;
+    mh.msg_controllen = sizeof(cmsgbuf);
+    mh.msg_flags = 0;
+
+    nread = recvmsg(pxping->sock6, &mh, 0);
+    if (nread < 0) {
+        DPRINTF(("%s: %R[sockerr]\n", __func__, SOCKERRNO()));
+        return;
+    }
+#else  /* RT_OS_WINDOWS */
+    mh.name = (LPSOCKADDR)&sin6;
+    mh.namelen = sizeof(sin6);
+    mh.lpBuffers = iov;
+    mh.dwBufferCount = 1;
+    mh.Control.buf = cmsgbuf;
+    mh.Control.len = sizeof(cmsgbuf);
+    mh.dwFlags = 0;
+
+    status = (*pxping->pfWSARecvMsg6)(pxping->sock6, &mh, &nread, NULL, NULL);
+    if (status == SOCKET_ERROR) {
+        DPRINTF2(("%s: error %d\n", __func__, WSAGetLastError()));
+        return;
+    }
+#endif
+
+    icmph = (struct icmp6_echo_hdr *)pollmgr_udpbuf;
+
+    DPRINTF2(("%s: %RTnaipv6 ICMPv6: ", __func__, &sin6.sin6_addr));
+
+    if (icmph->type == ICMP6_TYPE_EREP) {
+        DPRINTF2(("echo reply %04x %u\n",
+                  (unsigned int)icmph->id, (unsigned int)icmph->seqno));
+    }
+    else { /* XXX */
+        if (icmph->type == ICMP6_TYPE_EREQ) {
+            DPRINTF2(("echo request %04x %u\n",
+                      (unsigned int)icmph->id, (unsigned int)icmph->seqno));
+        }
+        else if (icmph->type == ICMP6_TYPE_DUR) {
+            DPRINTF2(("destination unreachable\n"));
+        }
+        else if (icmph->type == ICMP6_TYPE_PTB) {
+            DPRINTF2(("packet too big\n"));
+        }
+        else if (icmph->type == ICMP6_TYPE_TE) {
+            DPRINTF2(("time exceeded\n"));
+        }
+        else if (icmph->type == ICMP6_TYPE_PP) {
+            DPRINTF2(("parameter problem\n"));
+        }
+        else {
+            DPRINTF2(("type %d len %u\n", icmph->type, (unsigned int)nread));
+        }
+
+        if (icmph->type >= ICMP6_TYPE_EREQ) {
+            return;             /* informational message */
+        }
+    }
+
+    pktinfo = NULL;
+    hopl = -1;
+    tclass = -1;
+    for (cmh = CMSG_FIRSTHDR(&mh); cmh != NULL; cmh = CMSG_NXTHDR(&mh, cmh)) {
+        if (cmh->cmsg_len == 0)
+            break;
+
+        if (cmh->cmsg_level == IPPROTO_IPV6
+            && cmh->cmsg_type == IPV6_HOPLIMIT
+            && cmh->cmsg_len == CMSG_LEN(sizeof(int)))
+        {
+            hopl = *(int *)CMSG_DATA(cmh);
+            DPRINTF2(("hoplimit = %d\n", hopl));
+        }
+
+        if (cmh->cmsg_level == IPPROTO_IPV6
+            && cmh->cmsg_type == IPV6_PKTINFO
+            && cmh->cmsg_len == CMSG_LEN(sizeof(struct in6_pktinfo)))
+        {
+            pktinfo = (struct in6_pktinfo *)CMSG_DATA(cmh);
+            DPRINTF2(("pktinfo found\n"));
+        }
+    }
+
+    if (pktinfo == NULL) {
+        /*
+         * ip6_output_if() doesn't do checksum for us so we need to
+         * manually recompute it - for this we must know the
+         * destination address of the pseudo-header that we will
+         * rewrite with guest's address.  (TODO: yeah, yeah, we can
+         * compute it from scratch...)
+         */
+        DPRINTF2(("%s: unable to get pktinfo\n", __func__));
+        return;
+    }
+
+    if (hopl < 0) {
+        hopl = LWIP_ICMP6_HL;
+    }
+
+    if (icmph->type == ICMP6_TYPE_EREP) {
+        pxping_pmgr_icmp6_echo(pxping,
+                               (ip6_addr_t *)&sin6.sin6_addr,
+                               (ip6_addr_t *)&pktinfo->ipi6_addr,
+                               hopl, tclass, (u16_t)nread);
+    }
+    else if (icmph->type < ICMP6_TYPE_EREQ) {
+        pxping_pmgr_icmp6_error(pxping,
+                                (ip6_addr_t *)&sin6.sin6_addr,
+                                (ip6_addr_t *)&pktinfo->ipi6_addr,
+                                hopl, tclass, (u16_t)nread);
+    }
+}
+
+
+/**
+ * Check if this incoming ICMPv6 echo reply is for one of our pings
+ * and forward it to the guest.
+ */
+static void
+pxping_pmgr_icmp6_echo(struct pxping *pxping,
+                       ip6_addr_t *src, ip6_addr_t *dst,
+                       int hopl, int tclass, u16_t icmplen)
+{
+    struct icmp6_echo_hdr *icmph;
+    ip6_addr_t guest_ip, target_ip;
+    int mapped;
+    struct ping_pcb *pcb;
+    u16_t id, guest_id;
+    u32_t sum;
+
+    ip6_addr_copy(target_ip, *src);
+    mapped = pxremap_inbound_ip6(&target_ip, &target_ip);
+    if (mapped == PXREMAP_FAILED) {
+        return;
+    }
+    else if (mapped == PXREMAP_ASIS) {
+        if (hopl == 1) {
+            DPRINTF2(("%s: dropping packet with ttl 1\n", __func__));
+            return;
+        }
+        --hopl;
+    }
+
+    icmph = (struct icmp6_echo_hdr *)pollmgr_udpbuf;
+    id = icmph->id;
+
+    sys_mutex_lock(&pxping->lock);
+    pcb = pxping_pcb_for_reply(pxping, 1, ip6_2_ipX(&target_ip), id);
+    if (pcb == NULL) {
+        sys_mutex_unlock(&pxping->lock);
+        DPRINTF2(("%s: no match\n", __func__));
+        return;
+    }
+
+    DPRINTF2(("%s: pcb %p\n", __func__, (void *)pcb));
+
+    /* save info before unlocking since pcb may expire */
+    ip6_addr_copy(guest_ip, *ipX_2_ip6(&pcb->src));
+    guest_id = pcb->guest_id;
+
+    sys_mutex_unlock(&pxping->lock);
+
+    /* rewrite ICMPv6 echo header */
+    sum = (u16_t)~icmph->chksum;
+    sum += chksum_update_16(&icmph->id, guest_id);
+    sum += chksum_delta_ipv6(dst, &guest_ip); /* pseudo */
+    if (mapped) {
+        sum += chksum_delta_ipv6(src, &target_ip); /* pseudo */
+    }
+    sum = FOLD_U32T(sum);
+    icmph->chksum = ~sum;
+
+    pxping_pmgr_forward_inbound6(pxping,
+                                 &target_ip, /* echo reply src */
+                                 &guest_ip, /* echo reply dst */
+                                 hopl, tclass, icmplen);
+}
+
+
+/**
+ * Check if this incoming ICMPv6 error is about one of our pings and
+ * forward it to the guest.
+ */
+static void
+pxping_pmgr_icmp6_error(struct pxping *pxping,
+                        ip6_addr_t *src, ip6_addr_t *dst,
+                        int hopl, int tclass, u16_t icmplen)
+{
+    struct icmp6_hdr *icmph;
+    u8_t *bufptr;
+    size_t buflen, hlen;
+    int proto;
+    struct ip6_hdr *oiph;
+    struct icmp6_echo_hdr *oicmph;
+    struct ping_pcb *pcb;
+    ip6_addr_t guest_ip, target_ip, error_ip;
+    int target_mapped, error_mapped;
+    u16_t guest_id;
+    u32_t sum;
+
+    icmph = (struct icmp6_hdr *)pollmgr_udpbuf;
+
+    /*
+     * Inner IP datagram is not checked by the kernel and may be
+     * anything, possibly malicious.
+     */
+    oiph = NULL;
+    oicmph = NULL;
+
+    bufptr = pollmgr_udpbuf;
+    buflen = icmplen;
+
+    hlen = sizeof(*icmph);
+    proto = IP6_NEXTH_ENCAPS; /* i.e. IPv6, lwIP's name is unfortuate */
+    for (;;) {
+        if (hlen > buflen) {
+            DPRINTF2(("truncated datagram inside ICMPv6 error message is too short\n"));
+            return;
+        }
+        buflen -= hlen;
+        bufptr += hlen;
+
+        if (proto == IP6_NEXTH_ENCAPS && oiph == NULL) { /* outermost IPv6 */
+            oiph = (struct ip6_hdr *)bufptr;
+            if (IP6H_V(oiph) != 6) {
+                DPRINTF2(("%s: unexpected IP version %d\n", __func__, IP6H_V(oiph)));
+                return;
+            }
+
+            proto = IP6H_NEXTH(oiph);
+            hlen = IP6_HLEN;
+        }
+        else if (proto == IP6_NEXTH_ICMP6) {
+            oicmph = (struct icmp6_echo_hdr *)bufptr;
+            break;
+        }
+        else if (proto == IP6_NEXTH_ROUTING
+                 || proto == IP6_NEXTH_HOPBYHOP
+                 || proto == IP6_NEXTH_DESTOPTS)
+        {
+            proto = bufptr[0];
+            hlen = (bufptr[1] + 1) * 8;
+        }
+        else {
+            DPRINTF2(("%s: stopping at protocol %d\n", __func__, proto));
+            break;
+        }
+    }
+
+    if (oiph == NULL || oicmph == NULL) {
+        return;
+    }
+
+    if (buflen < sizeof(*oicmph)) {
+        DPRINTF2(("%s: original ICMPv6 is truncated too short\n", __func__));
+        return;
+    }
+
+    if (oicmph->type != ICMP6_TYPE_EREQ) {
+        DPRINTF2(("%s: ignoring original ICMPv6 type %d\n", __func__, oicmph->type));
+        return;
+    }
+
+    ip6_addr_copy(target_ip, oiph->dest); /* inner (failed) */
+    target_mapped = pxremap_inbound_ip6(&target_ip, &target_ip);
+    if (target_mapped == PXREMAP_FAILED) {
+        return;
+    }
+
+    sys_mutex_lock(&pxping->lock);
+    pcb = pxping_pcb_for_reply(pxping, 1, ip6_2_ipX(&target_ip), oicmph->id);
+    if (pcb == NULL) {
+        sys_mutex_unlock(&pxping->lock);
+        DPRINTF2(("%s: no match\n", __func__));
+        return;
+    }
+
+    DPRINTF2(("%s: pcb %p\n", __func__, (void *)pcb));
+
+    /* save info before unlocking since pcb may expire */
+    ip6_addr_copy(guest_ip, *ipX_2_ip6(&pcb->src));
+    guest_id = pcb->guest_id;
+
+    sys_mutex_unlock(&pxping->lock);
+
+
+    /*
+     * Rewrite inner and outer headers and forward to guest.  Note
+     * that IPv6 has no IP header checksum, but uses pseudo-header for
+     * ICMPv6, so we update both in one go, adjusting ICMPv6 checksum
+     * as we rewrite IP header.
+     */
+
+    ip6_addr_copy(error_ip, *src); /* node that reports the error */
+    error_mapped = pxremap_inbound_ip6(&error_ip, &error_ip);
+    if (error_mapped == PXREMAP_FAILED) {
+        return;
+    }
+    if (error_mapped == PXREMAP_ASIS && hopl == 1) {
+        DPRINTF2(("%s: dropping packet with ttl 1\n", __func__));
+        return;
+    }
+
+    /* rewrite inner ICMPv6 echo header and inner IPv6 header */
+    sum = (u16_t)~oicmph->chksum;
+    sum += chksum_update_16(&oicmph->id, guest_id);
+    sum += chksum_update_ipv6((ip6_addr_t *)&oiph->src, &guest_ip);
+    if (target_mapped) {
+        sum += chksum_delta_ipv6((ip6_addr_t *)&oiph->dest, &target_ip);
+    }
+    sum = FOLD_U32T(sum);
+    oicmph->chksum = ~sum;
+
+    /* rewrite outer ICMPv6 error header */
+    sum = (u16_t)~icmph->chksum;
+    sum += chksum_delta_ipv6(dst, &guest_ip); /* pseudo */
+    if (error_mapped) {
+        sum += chksum_delta_ipv6(src, &error_ip); /* pseudo */
+    }
+    sum = FOLD_U32T(sum);
+    icmph->chksum = ~sum;
+
+    pxping_pmgr_forward_inbound6(pxping,
+                                 &error_ip, /* error src */
+                                 &guest_ip, /* error dst */
+                                 hopl, tclass, icmplen);
+}
+
+
+/**
+ * Hand off ICMP datagram to the lwip thread where it will be
+ * forwarded to the guest.
+ *
+ * We no longer need ping_pcb.  The pcb may get expired on the lwip
+ * thread, but we have already patched necessary information into the
+ * datagram.
+ */
+static void
+pxping_pmgr_forward_inbound(struct pxping *pxping, u16_t iplen)
+{
+    struct pbuf *p;
+    struct ping_msg *msg;
+    err_t error;
+
+    p = pbuf_alloc(PBUF_LINK, iplen, PBUF_RAM);
+    if (p == NULL) {
+        DPRINTF(("%s: pbuf_alloc(%d) failed\n",
+                 __func__, (unsigned int)iplen));
+        return;
+    }
+
+    error = pbuf_take(p, pollmgr_udpbuf, iplen);
+    if (error != ERR_OK) {
+        DPRINTF(("%s: pbuf_take(%d) failed\n",
+                 __func__, (unsigned int)iplen));
+        pbuf_free(p);
+        return;
+    }
+
+    msg = (struct ping_msg *)malloc(sizeof(*msg));
+    if (msg == NULL) {
+        pbuf_free(p);
+        return;
+    }
+
+    msg->msg.type = TCPIP_MSG_CALLBACK_STATIC;
+    msg->msg.sem = NULL;
+    msg->msg.msg.cb.function = pxping_pcb_forward_inbound;
+    msg->msg.msg.cb.ctx = (void *)msg;
+
+    msg->pxping = pxping;
+    msg->p = p;
+
+    proxy_lwip_post(&msg->msg);
+}
+
+
+static void
+pxping_pcb_forward_inbound(void *arg)
+{
+    struct ping_msg *msg = (struct ping_msg *)arg;
+    err_t error;
+
+    LWIP_ASSERT1(msg != NULL);
+    LWIP_ASSERT1(msg->pxping != NULL);
+    LWIP_ASSERT1(msg->p != NULL);
+
+    error = ip_raw_output_if(msg->p, msg->pxping->netif);
+    if (error != ERR_OK) {
+        DPRINTF(("%s: ip_output_if: %s\n",
+                 __func__, proxy_lwip_strerr(error)));
+    }
+    pbuf_free(msg->p);
+    free(msg);
+}
+
+
+static void
+pxping_pmgr_forward_inbound6(struct pxping *pxping,
+                             ip6_addr_t *src, ip6_addr_t *dst,
+                             u8_t hopl, u8_t tclass,
+                             u16_t icmplen)
+{
+    struct pbuf *p;
+    struct ping6_msg *msg;
+
+    err_t error;
+
+    p = pbuf_alloc(PBUF_IP, icmplen, PBUF_RAM);
+    if (p == NULL) {
+        DPRINTF(("%s: pbuf_alloc(%d) failed\n",
+                 __func__, (unsigned int)icmplen));
+        return;
+    }
+
+    error = pbuf_take(p, pollmgr_udpbuf, icmplen);
+    if (error != ERR_OK) {
+        DPRINTF(("%s: pbuf_take(%d) failed\n",
+                 __func__, (unsigned int)icmplen));
+        pbuf_free(p);
+        return;
+    }
+
+    msg = (struct ping6_msg *)malloc(sizeof(*msg));
+    if (msg == NULL) {
+        pbuf_free(p);
+        return;
+    }
+
+    msg->msg.type = TCPIP_MSG_CALLBACK_STATIC;
+    msg->msg.sem = NULL;
+    msg->msg.msg.cb.function = pxping_pcb_forward_inbound6;
+    msg->msg.msg.cb.ctx = (void *)msg;
+
+    msg->pxping = pxping;
+    msg->p = p;
+    ip6_addr_copy(msg->src, *src);
+    ip6_addr_copy(msg->dst, *dst);
+    msg->hopl = hopl;
+    msg->tclass = tclass;
+
+    proxy_lwip_post(&msg->msg);
+}
+
+
+static void
+pxping_pcb_forward_inbound6(void *arg)
+{
+    struct ping6_msg *msg = (struct ping6_msg *)arg;
+    err_t error;
+
+    LWIP_ASSERT1(msg != NULL);
+    LWIP_ASSERT1(msg->pxping != NULL);
+    LWIP_ASSERT1(msg->p != NULL);
+
+    error = ip6_output_if(msg->p,
+                          &msg->src, &msg->dst, msg->hopl, msg->tclass,
+                          IP6_NEXTH_ICMP6, msg->pxping->netif);
+    if (error != ERR_OK) {
+        DPRINTF(("%s: ip6_output_if: %s\n",
+                 __func__, proxy_lwip_strerr(error)));
+    }
+    pbuf_free(msg->p);
+    free(msg);
+}
diff --git a/src/VBox/NetworkServices/NAT/pxping_win.c b/src/VBox/NetworkServices/NAT/pxping_win.c
new file mode 100644
index 00000000..2c6da8fd
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/pxping_win.c
@@ -0,0 +1,672 @@
+/* $Id: pxping_win.c $ */
+/** @file
+ * NAT Network - ping proxy, Windows ICMP API version.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#define LOG_GROUP LOG_GROUP_NAT_SERVICE
+
+#include "winutils.h"
+#include "proxy.h"
+#include "pxremap.h"
+
+#include "lwip/ip.h"
+#include "lwip/icmp.h"
+#include "lwip/inet_chksum.h"
+
+/* XXX: lwIP names conflict with winsock <iphlpapi.h> */
+#undef IP_STATS
+#undef ICMP_STATS
+#undef TCP_STATS
+#undef UDP_STATS
+#undef IP6_STATS
+
+#include <winternl.h>           /* for PIO_APC_ROUTINE &c */
+#ifndef PIO_APC_ROUTINE_DEFINED
+# define PIO_APC_ROUTINE_DEFINED 1
+#endif
+#include <iprt/win/iphlpapi.h>
+#include <icmpapi.h>
+
+#include <stdio.h>
+
+
+struct pxping {
+    /*
+     * We use single ICMP handle for all pings.  This means that all
+     * proxied pings will have the same id and share single sequence
+     * of sequence numbers.
+     */
+    HANDLE hdl4;
+    HANDLE hdl6;
+
+    struct netif *netif;
+
+    /*
+     * On Windows XP and Windows Server 2003 IcmpSendEcho2() callback
+     * is FARPROC, but starting from Vista it's PIO_APC_ROUTINE with
+     * two extra arguments.  Callbacks use WINAPI (stdcall) calling
+     * convention with callee responsible for popping the arguments,
+     * so to avoid stack corruption we check windows version at run
+     * time and provide correct callback.
+     */
+    PIO_APC_ROUTINE pfnCallback4;
+    PIO_APC_ROUTINE pfnCallback6;
+};
+
+
+struct pong4 {
+    struct netif *netif;
+
+    struct ip_hdr reqiph;
+    struct icmp_echo_hdr reqicmph;
+
+    size_t bufsize;
+    u8_t buf[1];
+};
+
+
+struct pong6 {
+    struct netif *netif;
+
+    ip6_addr_t reqsrc;
+    struct icmp6_echo_hdr reqicmph;
+    size_t reqsize;
+
+    size_t bufsize;
+    u8_t buf[1];
+};
+
+
+static void pxping_recv4(void *arg, struct pbuf *p);
+static void pxping_recv6(void *arg, struct pbuf *p);
+
+static VOID WINAPI pxping_icmp4_callback_old(void *);
+static VOID WINAPI pxping_icmp4_callback_apc(void *, PIO_STATUS_BLOCK, ULONG);
+static void pxping_icmp4_callback(struct pong4 *pong);
+
+static VOID WINAPI pxping_icmp6_callback_old(void *);
+static VOID WINAPI pxping_icmp6_callback_apc(void *, PIO_STATUS_BLOCK, ULONG);
+static void pxping_icmp6_callback(struct pong6 *pong);
+
+
+struct pxping g_pxping;
+
+
+err_t
+pxping_init(struct netif *netif, SOCKET sock4, SOCKET sock6)
+{
+    OSVERSIONINFO osvi;
+    int status;
+
+    LWIP_UNUSED_ARG(sock4);
+    LWIP_UNUSED_ARG(sock6);
+
+    ZeroMemory(&osvi, sizeof(OSVERSIONINFO));
+    osvi.dwOSVersionInfoSize = sizeof(OSVERSIONINFO);
+    status = GetVersionEx(&osvi);
+    if (status == 0) {
+        return ERR_ARG;
+    }
+
+    if (osvi.dwMajorVersion >= 6) {
+        g_pxping.pfnCallback4 = pxping_icmp4_callback_apc;
+        g_pxping.pfnCallback6 = pxping_icmp6_callback_apc;
+    }
+    else {
+        g_pxping.pfnCallback4 = (PIO_APC_ROUTINE)pxping_icmp4_callback_old;
+        g_pxping.pfnCallback6 = (PIO_APC_ROUTINE)pxping_icmp6_callback_old;
+    }
+
+
+    g_pxping.hdl4 = IcmpCreateFile();
+    if (g_pxping.hdl4 != INVALID_HANDLE_VALUE) {
+        ping_proxy_accept(pxping_recv4, &g_pxping);
+    }
+    else {
+        DPRINTF(("IcmpCreateFile: error %d\n", GetLastError()));
+    }
+
+    g_pxping.hdl6 = Icmp6CreateFile();
+    if (g_pxping.hdl6 != INVALID_HANDLE_VALUE) {
+        ping6_proxy_accept(pxping_recv6, &g_pxping);
+    }
+    else {
+        DPRINTF(("Icmp6CreateFile: error %d\n", GetLastError()));
+    }
+
+    if (g_pxping.hdl4 == INVALID_HANDLE_VALUE
+        && g_pxping.hdl6 == INVALID_HANDLE_VALUE)
+    {
+        return ERR_ARG;
+    }
+
+    g_pxping.netif = netif;
+
+    return ERR_OK;
+}
+
+
+/**
+ * ICMP Echo Request in pbuf "p" is to be proxied.
+ */
+static void
+pxping_recv4(void *arg, struct pbuf *p)
+{
+    struct pxping *pxping = (struct pxping *)arg;
+    const struct ip_hdr *iph;
+    const struct icmp_echo_hdr *icmph;
+    u16_t iphlen;
+    size_t bufsize;
+    struct pong4 *pong;
+    IPAddr dst;
+    int mapped;
+    int ttl;
+    IP_OPTION_INFORMATION opts;
+    void *reqdata;
+    size_t reqsize;
+    int status;
+
+    pong = NULL;
+
+    iphlen = ip_current_header_tot_len();
+    if (RT_UNLIKELY(iphlen != IP_HLEN)) { /* we don't do options */
+        goto out;
+    }
+
+    iph = (const struct ip_hdr *)ip_current_header();
+    icmph = (const struct icmp_echo_hdr *)p->payload;
+
+    mapped = pxremap_outbound_ip4((ip_addr_t *)&dst, (ip_addr_t *)&iph->dest);
+    if (RT_UNLIKELY(mapped == PXREMAP_FAILED)) {
+        goto out;
+    }
+
+    ttl = IPH_TTL(iph);
+    if (mapped == PXREMAP_ASIS) {
+        if (RT_UNLIKELY(ttl == 1)) {
+            status = pbuf_header(p, iphlen); /* back to IP header */
+            if (RT_LIKELY(status == 0)) {
+                icmp_time_exceeded(p, ICMP_TE_TTL);
+            }
+            goto out;
+        }
+        --ttl;
+    }
+
+    status = pbuf_header(p, -(u16_t)sizeof(*icmph)); /* to ping payload */
+    if (RT_UNLIKELY(status != 0)) {
+        goto out;
+    }
+
+    bufsize = sizeof(ICMP_ECHO_REPLY);
+    if (p->tot_len < sizeof(IO_STATUS_BLOCK) + sizeof(struct icmp_echo_hdr))
+        bufsize += sizeof(IO_STATUS_BLOCK) + sizeof(struct icmp_echo_hdr);
+    else
+        bufsize += p->tot_len;
+    bufsize += 16; /* whatever that is; empirically at least XP needs it */
+
+    pong = (struct pong4 *)malloc(RT_UOFFSETOF(struct pong4, buf) + bufsize);
+    if (RT_UNLIKELY(pong == NULL)) {
+        goto out;
+    }
+    pong->bufsize = bufsize;
+    pong->netif = pxping->netif;
+
+    memcpy(&pong->reqiph, iph, sizeof(*iph));
+    memcpy(&pong->reqicmph, icmph, sizeof(*icmph));
+
+    reqsize = p->tot_len;
+    if (p->next == NULL) {
+        /* single pbuf can be directly used as request data source */
+        reqdata = p->payload;
+    }
+    else {
+        /* data from pbuf chain must be concatenated */
+        pbuf_copy_partial(p, pong->buf, p->tot_len, 0);
+        reqdata = pong->buf;
+    }
+
+    opts.Ttl = ttl;
+    opts.Tos = IPH_TOS(iph); /* affected by DisableUserTOSSetting key */
+    opts.Flags = (IPH_OFFSET(iph) & PP_HTONS(IP_DF)) != 0 ? IP_FLAG_DF : 0;
+    opts.OptionsSize = 0;
+    opts.OptionsData = 0;
+
+    status = IcmpSendEcho2(pxping->hdl4, NULL,
+                           pxping->pfnCallback4, pong,
+                           dst, reqdata, (WORD)reqsize, &opts,
+                           pong->buf, (DWORD)pong->bufsize,
+                           5 * 1000 /* ms */);
+
+    if (RT_UNLIKELY(status != 0)) {
+        DPRINTF(("IcmpSendEcho2: unexpected status %d\n", status));
+        goto out;
+    }
+    if ((status = GetLastError()) != ERROR_IO_PENDING) {
+        int code;
+
+        DPRINTF(("IcmpSendEcho2: error %d\n", status));
+        switch (status) {
+        case ERROR_NETWORK_UNREACHABLE:
+            code = ICMP_DUR_NET;
+            break;
+        case ERROR_HOST_UNREACHABLE:
+            code = ICMP_DUR_HOST;
+            break;
+        default:
+            code = -1;
+            break;
+        }
+
+        if (code != -1) {
+            /* move payload back to IP header */
+            status = pbuf_header(p, (u16_t)(sizeof(*icmph) + iphlen));
+            if (RT_LIKELY(status == 0)) {
+                icmp_dest_unreach(p, code);
+            }
+        }
+        goto out;
+    }
+
+    pong = NULL;                /* callback owns it now */
+  out:
+    if (pong != NULL) {
+        free(pong);
+    }
+    pbuf_free(p);
+}
+
+
+static VOID WINAPI
+pxping_icmp4_callback_apc(void *ctx, PIO_STATUS_BLOCK iob, ULONG reserved)
+{
+    struct pong4 *pong = (struct pong4 *)ctx;
+    LWIP_UNUSED_ARG(iob);
+    LWIP_UNUSED_ARG(reserved);
+
+    if (pong != NULL) {
+        pxping_icmp4_callback(pong);
+        free(pong);
+    }
+}
+
+
+static VOID WINAPI
+pxping_icmp4_callback_old(void *ctx)
+{
+    struct pong4 *pong = (struct pong4 *)ctx;
+
+    if (pong != NULL) {
+        pxping_icmp4_callback(pong);
+        free(pong);
+    }
+}
+
+
+static void
+pxping_icmp4_callback(struct pong4 *pong)
+{
+    ICMP_ECHO_REPLY *reply;
+    DWORD nreplies;
+    size_t icmplen;
+    struct pbuf *p;
+    struct icmp_echo_hdr *icmph;
+    ip_addr_t src;
+    int mapped;
+
+    nreplies = IcmpParseReplies(pong->buf, (DWORD)pong->bufsize);
+    if (nreplies == 0) {
+        DWORD error = GetLastError();
+        if (error == IP_REQ_TIMED_OUT) {
+            DPRINTF2(("pong4: %p timed out\n", (void *)pong));
+        }
+        else {
+            DPRINTF(("pong4: %p: IcmpParseReplies: error %d\n",
+                     (void *)pong, error));
+        }
+        return;
+    }
+
+    reply = (ICMP_ECHO_REPLY *)pong->buf;
+
+    if (reply->Options.OptionsSize != 0) { /* don't do options */
+        return;
+    }
+
+    mapped = pxremap_inbound_ip4(&src, (ip_addr_t *)&reply->Address);
+    if (mapped == PXREMAP_FAILED) {
+        return;
+    }
+    if (mapped == PXREMAP_ASIS) {
+        if (reply->Options.Ttl == 1) {
+            return;
+        }
+        --reply->Options.Ttl;
+    }
+
+    if (reply->Status == IP_SUCCESS) {
+        icmplen = sizeof(struct icmp_echo_hdr) + reply->DataSize;
+        if ((reply->Options.Flags & IP_FLAG_DF) != 0
+            && IP_HLEN + icmplen > pong->netif->mtu)
+        {
+            return;
+        }
+
+        p = pbuf_alloc(PBUF_IP, (u16_t)icmplen, PBUF_RAM);
+        if (RT_UNLIKELY(p == NULL)) {
+            return;
+        }
+
+        icmph = (struct icmp_echo_hdr *)p->payload;
+        icmph->type = ICMP_ER;
+        icmph->code = 0;
+        icmph->chksum = 0;
+        icmph->id = pong->reqicmph.id;
+        icmph->seqno = pong->reqicmph.seqno;
+
+        memcpy((u8_t *)p->payload + sizeof(*icmph),
+               reply->Data, reply->DataSize);
+    }
+    else {
+        u8_t type, code;
+
+        switch (reply->Status) {
+        case IP_DEST_NET_UNREACHABLE:
+            type = ICMP_DUR; code = ICMP_DUR_NET;
+            break;
+        case IP_DEST_HOST_UNREACHABLE:
+            type = ICMP_DUR; code = ICMP_DUR_HOST;
+            break;
+        case IP_DEST_PROT_UNREACHABLE:
+            type = ICMP_DUR; code = ICMP_DUR_PROTO;
+            break;
+        case IP_PACKET_TOO_BIG:
+            type = ICMP_DUR; code = ICMP_DUR_FRAG;
+            break;
+        case IP_SOURCE_QUENCH:
+            type = ICMP_SQ; code = 0;
+            break;
+        case IP_TTL_EXPIRED_TRANSIT:
+            type = ICMP_TE; code = ICMP_TE_TTL;
+            break;
+        case IP_TTL_EXPIRED_REASSEM:
+            type = ICMP_TE; code = ICMP_TE_FRAG;
+            break;
+        default:
+            DPRINTF(("pong4: reply status %d, dropped\n", reply->Status));
+            return;
+        }
+
+        DPRINTF(("pong4: reply status %d -> type %d/code %d\n",
+                 reply->Status, type, code));
+
+        icmplen = sizeof(*icmph) + sizeof(pong->reqiph) + sizeof(pong->reqicmph);
+
+        p = pbuf_alloc(PBUF_IP, (u16_t)icmplen, PBUF_RAM);
+        if (RT_UNLIKELY(p == NULL)) {
+            return;
+        }
+
+        icmph = (struct icmp_echo_hdr *)p->payload;
+        icmph->type = type;
+        icmph->code = code;
+        icmph->chksum = 0;
+        icmph->id = 0;
+        icmph->seqno = 0;
+
+        /*
+         * XXX: we don't know the TTL of the request at the time this
+         * ICMP error was generated (we can guess it was 1 for ttl
+         * exceeded, but don't bother faking it).
+         */
+        memcpy((u8_t *)p->payload + sizeof(*icmph),
+               &pong->reqiph, sizeof(pong->reqiph));
+
+        memcpy((u8_t *)p->payload + sizeof(*icmph) + sizeof(pong->reqiph),
+               &pong->reqicmph, sizeof(pong->reqicmph));
+    }
+
+    icmph->chksum = inet_chksum(p->payload, (u16_t)icmplen);
+    ip_output_if(p, &src,
+                 (ip_addr_t *)&pong->reqiph.src, /* dst */
+                 reply->Options.Ttl,
+                 reply->Options.Tos,
+                 IPPROTO_ICMP,
+                 pong->netif);
+    pbuf_free(p);
+}
+
+
+static void
+pxping_recv6(void *arg, struct pbuf *p)
+{
+    struct pxping *pxping = (struct pxping *)arg;
+    struct icmp6_echo_hdr *icmph;
+    size_t bufsize;
+    struct pong6 *pong;
+    int mapped;
+    void *reqdata;
+    size_t reqsize;
+    struct sockaddr_in6 src, dst;
+    int hopl;
+    IP_OPTION_INFORMATION opts;
+    int status;
+
+    pong = NULL;
+
+    icmph = (struct icmp6_echo_hdr *)p->payload;
+
+    memset(&dst, 0, sizeof(dst));
+    dst.sin6_family = AF_INET6;
+    mapped = pxremap_outbound_ip6((ip6_addr_t *)&dst.sin6_addr,
+                                  ip6_current_dest_addr());
+    if (RT_UNLIKELY(mapped == PXREMAP_FAILED)) {
+        goto out;
+    }
+
+    hopl = IP6H_HOPLIM(ip6_current_header());
+    if (mapped == PXREMAP_ASIS) {
+        if (RT_UNLIKELY(hopl == 1)) {
+            status = pbuf_header(p, ip_current_header_tot_len());
+            if (RT_LIKELY(status == 0)) {
+                icmp6_time_exceeded(p, ICMP6_TE_HL);
+            }
+            goto out;
+        }
+        --hopl;
+    }
+
+    status = pbuf_header(p, -(u16_t)sizeof(*icmph)); /* to ping payload */
+    if (RT_UNLIKELY(status != 0)) {
+        goto out;
+    }
+
+    /* XXX: parrotted from IPv4 version, not tested all os version/bitness */
+    bufsize = sizeof(ICMPV6_ECHO_REPLY);
+    if (p->tot_len < sizeof(IO_STATUS_BLOCK) + sizeof(struct icmp6_echo_hdr))
+        bufsize += sizeof(IO_STATUS_BLOCK) + sizeof(struct icmp6_echo_hdr);
+    else
+        bufsize += p->tot_len;
+    bufsize += 16;
+
+    pong = (struct pong6 *)malloc(RT_UOFFSETOF(struct pong6, buf) + bufsize);
+    if (RT_UNLIKELY(pong == NULL)) {
+        goto out;
+    }
+    pong->bufsize = bufsize;
+    pong->netif = pxping->netif;
+
+    ip6_addr_copy(pong->reqsrc, *ip6_current_src_addr());
+    memcpy(&pong->reqicmph, icmph, sizeof(*icmph));
+
+    memset(pong->buf, 0xa5, pong->bufsize);
+
+    pong->reqsize = reqsize = p->tot_len;
+    if (p->next == NULL) {
+        /* single pbuf can be directly used as request data source */
+        reqdata = p->payload;
+    }
+    else {
+        /* data from pbuf chain must be concatenated */
+        pbuf_copy_partial(p, pong->buf, p->tot_len, 0);
+        reqdata = pong->buf;
+    }
+
+    memset(&src, 0, sizeof(src));
+    src.sin6_family = AF_INET6;
+    src.sin6_addr = in6addr_any; /* let the OS select host source address */
+
+    memset(&opts, 0, sizeof(opts));
+    opts.Ttl = hopl;
+
+    status = Icmp6SendEcho2(pxping->hdl6, NULL,
+                            pxping->pfnCallback6, pong,
+                            &src, &dst, reqdata, (WORD)reqsize, &opts,
+                            pong->buf, (DWORD)pong->bufsize,
+                            5 * 1000 /* ms */);
+
+    if (RT_UNLIKELY(status != 0)) {
+        DPRINTF(("Icmp6SendEcho2: unexpected status %d\n", status));
+        goto out;
+    }
+    if ((status = GetLastError()) != ERROR_IO_PENDING) {
+        int code;
+
+        DPRINTF(("Icmp6SendEcho2: error %d\n", status));
+        switch (status) {
+        case ERROR_NETWORK_UNREACHABLE:
+        case ERROR_HOST_UNREACHABLE:
+            code = ICMP6_DUR_NO_ROUTE;
+            break;
+        default:
+            code = -1;
+            break;
+        }
+
+        if (code != -1) {
+            /* move payload back to IP header */
+            status = pbuf_header(p, (u16_t)(sizeof(*icmph)
+                                            + ip_current_header_tot_len()));
+            if (RT_LIKELY(status == 0)) {
+                icmp6_dest_unreach(p, code);
+            }
+        }
+        goto out;
+    }
+
+    pong = NULL;                /* callback owns it now */
+  out:
+    if (pong != NULL) {
+        free(pong);
+    }
+    pbuf_free(p);
+}
+
+
+static VOID WINAPI
+pxping_icmp6_callback_apc(void *ctx, PIO_STATUS_BLOCK iob, ULONG reserved)
+{
+    struct pong6 *pong = (struct pong6 *)ctx;
+    LWIP_UNUSED_ARG(iob);
+    LWIP_UNUSED_ARG(reserved);
+
+    if (pong != NULL) {
+        pxping_icmp6_callback(pong);
+        free(pong);
+    }
+}
+
+
+static VOID WINAPI
+pxping_icmp6_callback_old(void *ctx)
+{
+    struct pong6 *pong = (struct pong6 *)ctx;
+
+    if (pong != NULL) {
+        pxping_icmp6_callback(pong);
+        free(pong);
+    }
+}
+
+
+static void
+pxping_icmp6_callback(struct pong6 *pong)
+{
+    DWORD nreplies;
+    ICMPV6_ECHO_REPLY *reply;
+    struct pbuf *p;
+    struct icmp6_echo_hdr *icmph;
+    size_t icmplen;
+    ip6_addr_t src;
+    int mapped;
+
+    nreplies = Icmp6ParseReplies(pong->buf, (DWORD)pong->bufsize);
+    if (nreplies == 0) {
+        DWORD error = GetLastError();
+        if (error == IP_REQ_TIMED_OUT) {
+            DPRINTF2(("pong6: %p timed out\n", (void *)pong));
+        }
+        else {
+            DPRINTF(("pong6: %p: Icmp6ParseReplies: error %d\n",
+                     (void *)pong, error));
+        }
+        return;
+    }
+
+    reply = (ICMPV6_ECHO_REPLY *)pong->buf;
+
+    mapped = pxremap_inbound_ip6(&src, (ip6_addr_t *)reply->Address.sin6_addr);
+    if (mapped == PXREMAP_FAILED) {
+        return;
+    }
+
+    /*
+     * Reply data follows ICMPV6_ECHO_REPLY structure in memory, but
+     * it doesn't tell us its size.  Assume it's equal the size of the
+     * request.
+     */
+    icmplen = sizeof(*icmph) + pong->reqsize;
+    p = pbuf_alloc(PBUF_IP, (u16_t)icmplen, PBUF_RAM);
+    if (RT_UNLIKELY(p == NULL)) {
+        return;
+    }
+
+    icmph = (struct icmp6_echo_hdr *)p->payload;
+    icmph->type = ICMP6_TYPE_EREP;
+    icmph->code = 0;
+    icmph->chksum = 0;
+    icmph->id = pong->reqicmph.id;
+    icmph->seqno = pong->reqicmph.seqno;
+
+    memcpy((u8_t *)p->payload + sizeof(*icmph),
+           pong->buf + sizeof(*reply), pong->reqsize);
+
+    icmph->chksum = ip6_chksum_pseudo(p, IP6_NEXTH_ICMP6, p->tot_len,
+                                      &src, &pong->reqsrc);
+    ip6_output_if(p, /* :src */ &src, /* :dst */ &pong->reqsrc,
+                  LWIP_ICMP6_HL, 0, IP6_NEXTH_ICMP6,
+                  pong->netif);
+    pbuf_free(p);
+}
diff --git a/src/VBox/NetworkServices/NAT/pxremap.c b/src/VBox/NetworkServices/NAT/pxremap.c
new file mode 100644
index 00000000..04d96591
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/pxremap.c
@@ -0,0 +1,333 @@
+/* $Id: pxremap.c $ */
+/** @file
+ * NAT Network - Loopback remapping.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+/*
+ * This file contains functions pertinent to magic address remapping.
+ *
+ * We want to expose host's loopback interfaces to the guest by
+ * mapping them to the addresses from the same prefix/subnet, so if,
+ * for example proxy interface is 10.0.2.1, we redirect traffic to
+ * 10.0.2.2 to host's 127.0.0.1 loopback.  If need be, we may extend
+ * this to provide additional mappings, e.g. 127.0.1.1 loopback
+ * address is used on Ubuntu 12.10+ for NetworkManager's dnsmasq.
+ *
+ * Ditto for IPv6, except that IPv6 only has one loopback address.
+ */
+#define LOG_GROUP LOG_GROUP_NAT_SERVICE
+
+#include "winutils.h"
+#include "pxremap.h"
+#include "proxy.h"
+
+#include "lwip/netif.h"
+#include "netif/etharp.h"       /* proxy arp hook */
+
+#include "lwip/ip4.h"           /* IPv4 divert hook */
+#include "lwip/ip6.h"           /* IPv6 divert hook */
+
+#include <string.h>
+
+
+/**
+ * Check if "dst" is an IPv4 address that proxy remaps to host's
+ * loopback.
+ */
+static int
+proxy_ip4_is_mapped_loopback(struct netif *netif, const ip_addr_t *dst, ip_addr_t *lo)
+{
+    u32_t off;
+    const struct ip4_lomap *lomap;
+    size_t i;
+
+    LWIP_ASSERT1(dst != NULL);
+
+    if (g_proxy_options->lomap_desc == NULL) {
+        return 0;
+    }
+
+    if (!ip_addr_netcmp(dst, &netif->ip_addr, &netif->netmask)) {
+        return 0;
+    }
+
+    /* XXX: TODO: check netif is a proxying netif! */
+
+    off = ntohl(ip4_addr_get_u32(dst) & ~ip4_addr_get_u32(&netif->netmask));
+    lomap = g_proxy_options->lomap_desc->lomap;
+    for (i = 0; i < g_proxy_options->lomap_desc->num_lomap; ++i) {
+        if (off == lomap[i].off) {
+            if (lo != NULL) {
+                ip_addr_copy(*lo, lomap[i].loaddr);
+            }
+            return 1;
+        }
+    }
+    return 0;
+}
+
+
+#if ARP_PROXY
+/**
+ * Hook function for etharp_arp_input() - returns true to cause proxy
+ * ARP reply to be generated for "dst".
+ */
+int
+pxremap_proxy_arp(struct netif *netif, ip_addr_t *dst)
+{
+    return proxy_ip4_is_mapped_loopback(netif, dst, NULL);
+}
+#endif /* ARP_PROXY */
+
+
+/**
+ * Hook function for ip_forward() - returns true to divert packets to
+ * "dst" to proxy (instead of forwarding them via "netif" or dropping).
+ */
+int
+pxremap_ip4_divert(struct netif *netif, ip_addr_t *dst)
+{
+    return proxy_ip4_is_mapped_loopback(netif, dst, NULL);
+}
+
+
+/**
+ * Mapping from local network to loopback for outbound connections.
+ *
+ * Copy "src" to "dst" with ip_addr_set(dst, src), but if "src" is a
+ * local network address that maps host's loopback address, copy
+ * loopback address to "dst".
+ */
+int
+pxremap_outbound_ip4(ip_addr_t *dst, ip_addr_t *src)
+{
+    struct netif *netif;
+
+    LWIP_ASSERT1(dst != NULL);
+    LWIP_ASSERT1(src != NULL);
+
+    for (netif = netif_list; netif != NULL; netif = netif->next) {
+        if (netif_is_up(netif) /* && this is a proxy netif */) {
+            if (proxy_ip4_is_mapped_loopback(netif, src, dst)) {
+                return PXREMAP_MAPPED;
+            }
+        }
+    }
+
+    /* not remapped, just copy src */
+    ip_addr_set(dst, src);
+    return PXREMAP_ASIS;
+}
+
+
+/**
+ * Mapping from loopback to local network for inbound (port-forwarded)
+ * connections.
+ *
+ * Copy "src" to "dst" with ip_addr_set(dst, src), but if "src" is a
+ * host's loopback address, copy local network address that maps it to
+ * "dst".
+ */
+int
+pxremap_inbound_ip4(ip_addr_t *dst, ip_addr_t *src)
+{
+    struct netif *netif;
+    const struct ip4_lomap *lomap;
+    unsigned int i;
+
+    if (ip4_addr1(src) != IP_LOOPBACKNET) {
+        ip_addr_set(dst, src);
+        return PXREMAP_ASIS;
+    }
+
+    if (g_proxy_options->lomap_desc == NULL) {
+        return PXREMAP_FAILED;
+    }
+
+#if 0 /* ?TODO: with multiple interfaces we need to consider fwspec::dst */
+    netif = ip_route(target);
+    if (netif == NULL) {
+        return PXREMAP_FAILED;
+    }
+#else
+    netif = netif_list;
+    LWIP_ASSERT1(netif != NULL);
+    LWIP_ASSERT1(netif->next == NULL);
+#endif
+
+    lomap = g_proxy_options->lomap_desc->lomap;
+    for (i = 0; i < g_proxy_options->lomap_desc->num_lomap; ++i) {
+        if (ip_addr_cmp(src, &lomap[i].loaddr)) {
+            ip_addr_t net;
+
+            ip_addr_get_network(&net, &netif->ip_addr, &netif->netmask);
+            ip4_addr_set_u32(dst,
+                             htonl(ntohl(ip4_addr_get_u32(&net))
+                                   + lomap[i].off));
+            return PXREMAP_MAPPED;
+        }
+    }
+
+    return PXREMAP_FAILED;
+}
+
+
+static int
+proxy_ip6_is_mapped_loopback(struct netif *netif, ip6_addr_t *dst)
+{
+    int i;
+
+    /* XXX: TODO: check netif is a proxying netif! */
+
+    LWIP_ASSERT1(dst != NULL);
+
+    for (i = 0; i < LWIP_IPV6_NUM_ADDRESSES; ++i) {
+        if (ip6_addr_ispreferred(netif_ip6_addr_state(netif, i))
+            && ip6_addr_isuniquelocal(netif_ip6_addr(netif, i)))
+        {
+            ip6_addr_t *ifaddr = netif_ip6_addr(netif, i);
+            if (memcmp(dst, ifaddr, sizeof(ip6_addr_t) - 1) == 0
+                && ((IP6_ADDR_BLOCK8(dst) & 0xff)
+                    == (IP6_ADDR_BLOCK8(ifaddr) & 0xff) + 1))
+            {
+                return 1;
+            }
+        }
+    }
+
+    return 0;
+}
+
+
+/**
+ * Hook function for nd6_input() - returns true to cause proxy NA
+ * reply to be generated for "dst".
+ */
+int
+pxremap_proxy_na(struct netif *netif, ip6_addr_t *dst)
+{
+    return proxy_ip6_is_mapped_loopback(netif, dst);
+}
+
+
+/**
+ * Hook function for ip6_forward() - returns true to divert packets to
+ * "dst" to proxy (instead of forwarding them via "netif" or dropping).
+ */
+int
+pxremap_ip6_divert(struct netif *netif, ip6_addr_t *dst)
+{
+    return proxy_ip6_is_mapped_loopback(netif, dst);
+}
+
+
+/**
+ * Mapping from local network to loopback for outbound connections.
+ *
+ * Copy "src" to "dst" with ip6_addr_set(dst, src), but if "src" is a
+ * local network address that maps host's loopback address, copy IPv6
+ * loopback address to "dst".
+ */
+int
+pxremap_outbound_ip6(ip6_addr_t *dst, ip6_addr_t *src)
+{
+    struct netif *netif;
+    int i;
+
+    LWIP_ASSERT1(dst != NULL);
+    LWIP_ASSERT1(src != NULL);
+
+    for (netif = netif_list; netif != NULL; netif = netif->next) {
+        if (!netif_is_up(netif) /* || this is not a proxy netif */) {
+            continue;
+        }
+
+        for (i = 0; i < LWIP_IPV6_NUM_ADDRESSES; ++i) {
+            if (ip6_addr_ispreferred(netif_ip6_addr_state(netif, i))
+                && ip6_addr_isuniquelocal(netif_ip6_addr(netif, i)))
+            {
+                ip6_addr_t *ifaddr = netif_ip6_addr(netif, i);
+                if (memcmp(src, ifaddr, sizeof(ip6_addr_t) - 1) == 0
+                    && ((IP6_ADDR_BLOCK8(src) & 0xff)
+                        == (IP6_ADDR_BLOCK8(ifaddr) & 0xff) + 1))
+                {
+                    ip6_addr_set_loopback(dst);
+                    return PXREMAP_MAPPED;
+                }
+            }
+        }
+    }
+
+    /* not remapped, just copy src */
+    ip6_addr_set(dst, src);
+    return PXREMAP_ASIS;
+}
+
+
+/**
+ * Mapping from loopback to local network for inbound (port-forwarded)
+ * connections.
+ *
+ * Copy "src" to "dst" with ip6_addr_set(dst, src), but if "src" is a
+ * host's loopback address, copy local network address that maps it to
+ * "dst".
+ */
+int
+pxremap_inbound_ip6(ip6_addr_t *dst, ip6_addr_t *src)
+{
+    ip6_addr_t loopback;
+    struct netif *netif;
+    int i;
+
+    ip6_addr_set_loopback(&loopback);
+    if (!ip6_addr_cmp(src, &loopback)) {
+        ip6_addr_set(dst, src);
+        return PXREMAP_ASIS;
+    }
+
+#if 0  /* ?TODO: with multiple interfaces we need to consider fwspec::dst */
+    netif = ip6_route_fwd(target);
+    if (netif == NULL) {
+        return PXREMAP_FAILED;
+    }
+#else
+    netif = netif_list;
+    LWIP_ASSERT1(netif != NULL);
+    LWIP_ASSERT1(netif->next == NULL);
+#endif
+
+    for (i = 0; i < LWIP_IPV6_NUM_ADDRESSES; ++i) {
+        ip6_addr_t *ifaddr = netif_ip6_addr(netif, i);
+        if (ip6_addr_ispreferred(netif_ip6_addr_state(netif, i))
+            && ip6_addr_isuniquelocal(ifaddr))
+        {
+            ip6_addr_set(dst, ifaddr);
+            ++((u8_t *)&dst->addr[3])[3];
+            return PXREMAP_MAPPED;
+        }
+    }
+
+    return PXREMAP_FAILED;
+}
diff --git a/src/VBox/NetworkServices/NAT/pxremap.h b/src/VBox/NetworkServices/NAT/pxremap.h
new file mode 100644
index 00000000..b99d8111
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/pxremap.h
@@ -0,0 +1,62 @@
+/* $Id: pxremap.h $ */
+/** @file
+ * NAT Network - Loopback remapping, declarations and definitions.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#ifndef VBOX_INCLUDED_SRC_NAT_pxremap_h
+#define VBOX_INCLUDED_SRC_NAT_pxremap_h
+#ifndef RT_WITHOUT_PRAGMA_ONCE
+# pragma once
+#endif
+
+#include "lwip/err.h"
+#include "lwip/ip_addr.h"
+
+struct netif;
+
+
+#define PXREMAP_FAILED (-1)
+#define PXREMAP_ASIS   0
+#define PXREMAP_MAPPED 1
+
+/* IPv4 */
+#if ARP_PROXY
+int pxremap_proxy_arp(struct netif *netif, ip_addr_t *dst);
+#endif
+int pxremap_ip4_divert(struct netif *netif, ip_addr_t *dst);
+int pxremap_outbound_ip4(ip_addr_t *dst, ip_addr_t *src);
+int pxremap_inbound_ip4(ip_addr_t *dst, ip_addr_t *src);
+
+/* IPv6 */
+int pxremap_proxy_na(struct netif *netif, ip6_addr_t *dst);
+int pxremap_ip6_divert(struct netif *netif, ip6_addr_t *dst);
+int pxremap_outbound_ip6(ip6_addr_t *dst, ip6_addr_t *src);
+int pxremap_inbound_ip6(ip6_addr_t *dst, ip6_addr_t *src);
+
+#define pxremap_outbound_ipX(is_ipv6, dst, src)                         \
+    ((is_ipv6) ? pxremap_outbound_ip6(&(dst)->ip6, &(src)->ip6)         \
+               : pxremap_outbound_ip4(&(dst)->ip4, &(src)->ip4))
+
+#endif /* !VBOX_INCLUDED_SRC_NAT_pxremap_h */
diff --git a/src/VBox/NetworkServices/NAT/pxtcp.c b/src/VBox/NetworkServices/NAT/pxtcp.c
new file mode 100644
index 00000000..716e9aff
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/pxtcp.c
@@ -0,0 +1,2524 @@
+/* $Id: pxtcp.c $ */
+/** @file
+ * NAT Network - TCP proxy.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#define LOG_GROUP LOG_GROUP_NAT_SERVICE
+
+#include "winutils.h"
+
+#include "pxtcp.h"
+
+#include "proxy.h"
+#include "proxy_pollmgr.h"
+#include "pxremap.h"
+#include "portfwd.h"            /* fwspec */
+
+#ifndef RT_OS_WINDOWS
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <sys/ioctl.h>
+#ifdef RT_OS_SOLARIS
+#include <sys/filio.h>          /* FIONREAD is BSD'ism */
+#endif
+#include <stdlib.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+#include <poll.h>
+
+#include <err.h>                /* BSD'ism */
+#else
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+
+#include <iprt/stdint.h>
+#include "winpoll.h"
+#endif
+
+#include "lwip/opt.h"
+
+#include "lwip/sys.h"
+#include "lwip/tcpip.h"
+#include "lwip/netif.h"
+#include "lwip/tcp_impl.h"      /* XXX: to access tcp_abandon() */
+#include "lwip/icmp.h"
+#include "lwip/icmp6.h"
+
+/*
+ * Different OSes have different quirks in reporting POLLHUP for TCP
+ * sockets.
+ *
+ * Using shutdown(2) "how" values here would be more readable, but
+ * since SHUT_RD is 0, we can't use 0 for "none", unfortunately.
+ */
+#if defined(RT_OS_NETBSD) || defined(RT_OS_SOLARIS)
+# define HAVE_TCP_POLLHUP 0                     /* not reported */
+#elif defined(RT_OS_DARWIN) || defined(RT_OS_WINDOWS)
+# define HAVE_TCP_POLLHUP POLLIN                /* reported when remote closes */
+#else
+# define HAVE_TCP_POLLHUP (POLLIN|POLLOUT)      /* reported when both directions are closed */
+#endif
+
+
+/**
+ * Ring buffer for inbound data.  Filled with data from the host
+ * socket on poll manager thread.  Data consumed by scheduling
+ * tcp_write() to the pcb on the lwip thread.
+ *
+ * NB: There is actually third party present, the lwip stack itself.
+ * Thus the buffer doesn't have dual free vs. data split, but rather
+ * three-way free / send and unACKed data / unsent data split.
+ */
+struct ringbuf {
+    char *buf;
+    size_t bufsize;
+
+    /*
+     * Start of free space, producer writes here (up till "unacked").
+     */
+    volatile size_t vacant;
+
+    /*
+     * Start of sent but unacknowledged data.  The data are "owned" by
+     * the stack as it may need to retransmit.  This is the free space
+     * limit for producer.
+     */
+    volatile size_t unacked;
+
+    /*
+     * Start of unsent data, consumer reads/sends from here (up till
+     * "vacant").  Not declared volatile since it's only accessed from
+     * the consumer thread.
+     */
+    size_t unsent;
+};
+
+
+/**
+ */
+struct pxtcp {
+    /**
+     * Our poll manager handler.  Must be first, strong/weak
+     * references depend on this "inheritance".
+     */
+    struct pollmgr_handler pmhdl;
+
+    /**
+     * lwIP (internal/guest) side of the proxied connection.
+     */
+    struct tcp_pcb *pcb;
+
+    /**
+     * Host (external) side of the proxied connection.
+     */
+    SOCKET sock;
+
+    /**
+     * Socket events we are currently polling for.
+     */
+    int events;
+
+    /**
+     * Socket error.  Currently used to save connect(2) errors so that
+     * we can decide if we need to send ICMP error.
+     */
+    int sockerr;
+
+    /**
+     * Interface that we have got the SYN from.  Needed to send ICMP
+     * with correct source address.
+     */
+    struct netif *netif;
+
+    /**
+     * For tentatively accepted connections for which we are in
+     * process of connecting to the real destination this is the
+     * initial pbuf that we might need to build ICMP error.
+     *
+     * When connection is established this is used to hold outbound
+     * pbuf chain received by pxtcp_pcb_recv() but not yet completely
+     * forwarded over the socket.  We cannot "return" it to lwIP since
+     * the head of the chain is already sent and freed.
+     */
+    struct pbuf *unsent;
+
+    /**
+     * Guest has closed its side. Reported to pxtcp_pcb_recv() only
+     * once and we might not be able to forward it immediately if we
+     * have unsent pbuf.
+     */
+    int outbound_close;
+
+    /**
+     * Outbound half-close has been done on the socket.
+     */
+    int outbound_close_done;
+
+    /**
+     * External has closed its side.  We might not be able to forward
+     * it immediately if we have unforwarded data.
+     */
+    int inbound_close;
+
+    /**
+     * Inbound half-close has been done on the pcb.
+     */
+    int inbound_close_done;
+
+    /**
+     * On systems that report POLLHUP as soon as the final FIN is
+     * received on a socket we cannot continue polling for the rest of
+     * input, so we have to read (pull) last data from the socket on
+     * the lwIP thread instead of polling/pushing it from the poll
+     * manager thread.  See comment in pxtcp_pmgr_pump() POLLHUP case.
+     */
+    int inbound_pull;
+
+
+    /**
+     * When poll manager schedules delete we may not be able to delete
+     * a pxtcp immediately if not all inbound data has been acked by
+     * the guest: lwIP may need to resend and the data are in pxtcp's
+     * inbuf::buf.  We defer delete until all data are acked to
+     * pxtcp_pcb_sent().
+     */
+    int deferred_delete;
+
+    /**
+     * Ring-buffer for inbound data.
+     */
+    struct ringbuf inbuf;
+
+    /**
+     * lwIP thread's strong reference to us.
+     */
+    struct pollmgr_refptr *rp;
+
+
+    /*
+     * We use static messages to call functions on the lwIP thread to
+     * void malloc/free overhead.
+     */
+    struct tcpip_msg msg_delete;   /* delete pxtcp */
+    struct tcpip_msg msg_reset;    /* reset connection and delete pxtcp */
+    struct tcpip_msg msg_accept;   /* confirm accept of proxied connection */
+    struct tcpip_msg msg_outbound; /* trigger send of outbound data */
+    struct tcpip_msg msg_inbound;  /* trigger send of inbound data */
+#if HAVE_TCP_POLLHUP
+    struct tcpip_msg msg_inpull;   /* trigger pull of last inbound data */
+#endif
+};
+
+
+
+static struct pxtcp *pxtcp_allocate(void);
+static void pxtcp_free(struct pxtcp *);
+
+static void pxtcp_pcb_associate(struct pxtcp *, struct tcp_pcb *);
+static void pxtcp_pcb_dissociate(struct pxtcp *);
+
+/* poll manager callbacks for pxtcp related channels */
+static int pxtcp_pmgr_chan_add(struct pollmgr_handler *, SOCKET, int);
+static int pxtcp_pmgr_chan_pollout(struct pollmgr_handler *, SOCKET, int);
+static int pxtcp_pmgr_chan_pollin(struct pollmgr_handler *, SOCKET, int);
+#if !(HAVE_TCP_POLLHUP & POLLOUT)
+static int pxtcp_pmgr_chan_del(struct pollmgr_handler *, SOCKET, int);
+#endif
+static int pxtcp_pmgr_chan_reset(struct pollmgr_handler *, SOCKET, int);
+
+/* helper functions for sending/receiving pxtcp over poll manager channels */
+static ssize_t pxtcp_chan_send(enum pollmgr_slot_t, struct pxtcp *);
+static ssize_t pxtcp_chan_send_weak(enum pollmgr_slot_t, struct pxtcp *);
+static struct pxtcp *pxtcp_chan_recv(struct pollmgr_handler *, SOCKET, int);
+static struct pxtcp *pxtcp_chan_recv_strong(struct pollmgr_handler *, SOCKET, int);
+
+/* poll manager callbacks for individual sockets */
+static int pxtcp_pmgr_connect(struct pollmgr_handler *, SOCKET, int);
+static int pxtcp_pmgr_pump(struct pollmgr_handler *, SOCKET, int);
+
+/* get incoming traffic into ring buffer */
+static ssize_t pxtcp_sock_read(struct pxtcp *, int *);
+static ssize_t pxtcp_sock_recv(struct pxtcp *, IOVEC *, size_t); /* default */
+
+/* convenience functions for poll manager callbacks */
+static int pxtcp_schedule_delete(struct pxtcp *);
+static int pxtcp_schedule_reset(struct pxtcp *);
+static int pxtcp_schedule_reject(struct pxtcp *);
+
+/* lwip thread callbacks called via proxy_lwip_post() */
+static void pxtcp_pcb_delete_pxtcp(void *);
+static void pxtcp_pcb_reset_pxtcp(void *);
+static void pxtcp_pcb_accept_refuse(void *);
+static void pxtcp_pcb_accept_confirm(void *);
+static void pxtcp_pcb_write_outbound(void *);
+static void pxtcp_pcb_write_inbound(void *);
+#if HAVE_TCP_POLLHUP
+static void pxtcp_pcb_pull_inbound(void *);
+#endif
+
+/* tcp pcb callbacks */
+static err_t pxtcp_pcb_heard(void *, struct tcp_pcb *, struct pbuf *); /* global */
+static err_t pxtcp_pcb_accept(void *, struct tcp_pcb *, err_t);
+static err_t pxtcp_pcb_connected(void *, struct tcp_pcb *, err_t);
+static err_t pxtcp_pcb_recv(void *, struct tcp_pcb *, struct pbuf *, err_t);
+static err_t pxtcp_pcb_sent(void *, struct tcp_pcb *, u16_t);
+static err_t pxtcp_pcb_poll(void *, struct tcp_pcb *);
+static void pxtcp_pcb_err(void *, err_t);
+
+static err_t pxtcp_pcb_forward_outbound(struct pxtcp *, struct pbuf *);
+static void pxtcp_pcb_forward_outbound_close(struct pxtcp *);
+
+static ssize_t pxtcp_sock_send(struct pxtcp *, IOVEC *, size_t);
+
+static void pxtcp_pcb_forward_inbound(struct pxtcp *);
+static void pxtcp_pcb_forward_inbound_close(struct pxtcp *);
+DECLINLINE(int) pxtcp_pcb_forward_inbound_done(const struct pxtcp *);
+static void pxtcp_pcb_schedule_poll(struct pxtcp *);
+static void pxtcp_pcb_cancel_poll(struct pxtcp *);
+
+static void pxtcp_pcb_reject(struct tcp_pcb *, int, struct netif *, struct pbuf *);
+DECLINLINE(void) pxtcp_pcb_maybe_deferred_delete(struct pxtcp *);
+
+/* poll manager handlers for pxtcp channels */
+static struct pollmgr_handler pxtcp_pmgr_chan_add_hdl;
+static struct pollmgr_handler pxtcp_pmgr_chan_pollout_hdl;
+static struct pollmgr_handler pxtcp_pmgr_chan_pollin_hdl;
+#if !(HAVE_TCP_POLLHUP & POLLOUT)
+static struct pollmgr_handler pxtcp_pmgr_chan_del_hdl;
+#endif
+static struct pollmgr_handler pxtcp_pmgr_chan_reset_hdl;
+
+
+/**
+ * Init PXTCP - must be run when neither lwIP tcpip thread, nor poll
+ * manager threads haven't been created yet.
+ */
+void
+pxtcp_init(void)
+{
+    /*
+     * Create channels.
+     */
+#define CHANNEL(SLOT, NAME) do {                \
+        NAME##_hdl.callback = NAME;             \
+        NAME##_hdl.data = NULL;                 \
+        NAME##_hdl.slot = -1;                   \
+        pollmgr_add_chan(SLOT, &NAME##_hdl);    \
+    } while (0)
+
+    CHANNEL(POLLMGR_CHAN_PXTCP_ADD,     pxtcp_pmgr_chan_add);
+    CHANNEL(POLLMGR_CHAN_PXTCP_POLLIN,  pxtcp_pmgr_chan_pollin);
+    CHANNEL(POLLMGR_CHAN_PXTCP_POLLOUT, pxtcp_pmgr_chan_pollout);
+#if !(HAVE_TCP_POLLHUP & POLLOUT)
+    CHANNEL(POLLMGR_CHAN_PXTCP_DEL,     pxtcp_pmgr_chan_del);
+#endif
+    CHANNEL(POLLMGR_CHAN_PXTCP_RESET,   pxtcp_pmgr_chan_reset);
+
+#undef CHANNEL
+
+    /*
+     * Listen to outgoing connection from guest(s).
+     */
+    tcp_proxy_accept(pxtcp_pcb_heard);
+}
+
+
+/**
+ * Syntactic sugar for sending pxtcp pointer over poll manager
+ * channel.  Used by lwip thread functions.
+ */
+static ssize_t
+pxtcp_chan_send(enum pollmgr_slot_t slot, struct pxtcp *pxtcp)
+{
+    return pollmgr_chan_send(slot, &pxtcp, sizeof(pxtcp));
+}
+
+
+/**
+ * Syntactic sugar for sending weak reference to pxtcp over poll
+ * manager channel.  Used by lwip thread functions.
+ */
+static ssize_t
+pxtcp_chan_send_weak(enum pollmgr_slot_t slot, struct pxtcp *pxtcp)
+{
+    pollmgr_refptr_weak_ref(pxtcp->rp);
+    return pollmgr_chan_send(slot, &pxtcp->rp, sizeof(pxtcp->rp));
+}
+
+
+/**
+ * Counterpart of pxtcp_chan_send().
+ */
+static struct pxtcp *
+pxtcp_chan_recv(struct pollmgr_handler *handler, SOCKET fd, int revents)
+{
+    struct pxtcp *pxtcp;
+
+    pxtcp = (struct pxtcp *)pollmgr_chan_recv_ptr(handler, fd, revents);
+    return pxtcp;
+}
+
+
+/**
+ * Counterpart of pxtcp_chan_send_weak().
+ */
+static struct pxtcp *
+pxtcp_chan_recv_strong(struct pollmgr_handler *handler, SOCKET fd, int revents)
+{
+    struct pollmgr_refptr *rp;
+    struct pollmgr_handler *base;
+    struct pxtcp *pxtcp;
+
+    rp = (struct pollmgr_refptr *)pollmgr_chan_recv_ptr(handler, fd, revents);
+    base = (struct pollmgr_handler *)pollmgr_refptr_get(rp);
+    pxtcp = (struct pxtcp *)base;
+
+    return pxtcp;
+}
+
+
+/**
+ * Register pxtcp with poll manager.
+ *
+ * Used for POLLMGR_CHAN_PXTCP_ADD and by port-forwarding.  Since
+ * error handling is different in these two cases, we leave it up to
+ * the caller.
+ */
+int
+pxtcp_pmgr_add(struct pxtcp *pxtcp)
+{
+    int status;
+
+    LWIP_ASSERT1(pxtcp != NULL);
+#ifdef RT_OS_WINDOWS
+    LWIP_ASSERT1(pxtcp->sock != INVALID_SOCKET);
+#else
+    LWIP_ASSERT1(pxtcp->sock >= 0);
+#endif
+    LWIP_ASSERT1(pxtcp->pmhdl.callback != NULL);
+    LWIP_ASSERT1(pxtcp->pmhdl.data == (void *)pxtcp);
+    LWIP_ASSERT1(pxtcp->pmhdl.slot < 0);
+
+    status = pollmgr_add(&pxtcp->pmhdl, pxtcp->sock, pxtcp->events);
+    return status;
+}
+
+
+/**
+ * Unregister pxtcp with poll manager.
+ *
+ * Used for POLLMGR_CHAN_PXTCP_RESET and by port-forwarding (on error
+ * leg).
+ */
+void
+pxtcp_pmgr_del(struct pxtcp *pxtcp)
+{
+    LWIP_ASSERT1(pxtcp != NULL);
+
+    pollmgr_del_slot(pxtcp->pmhdl.slot);
+}
+
+
+/**
+ * POLLMGR_CHAN_PXTCP_ADD handler.
+ *
+ * Get new pxtcp from lwip thread and start polling its socket.
+ */
+static int
+pxtcp_pmgr_chan_add(struct pollmgr_handler *handler, SOCKET fd, int revents)
+{
+    struct pxtcp *pxtcp;
+    int status;
+
+    pxtcp = pxtcp_chan_recv(handler, fd, revents);
+    DPRINTF0(("pxtcp_add: new pxtcp %p; pcb %p; sock %d\n",
+              (void *)pxtcp, (void *)pxtcp->pcb, pxtcp->sock));
+
+    status = pxtcp_pmgr_add(pxtcp);
+    if (status < 0) {
+        (void) pxtcp_schedule_reset(pxtcp);
+    }
+
+    return POLLIN;
+}
+
+
+/**
+ * POLLMGR_CHAN_PXTCP_POLLOUT handler.
+ *
+ * pxtcp_pcb_forward_outbound() on the lwIP thread tried to send data
+ * and failed, it now requests us to poll the socket for POLLOUT and
+ * schedule pxtcp_pcb_forward_outbound() when sock is writable again.
+ */
+static int
+pxtcp_pmgr_chan_pollout(struct pollmgr_handler *handler, SOCKET fd, int revents)
+{
+    struct pxtcp *pxtcp;
+
+    pxtcp = pxtcp_chan_recv_strong(handler, fd, revents);
+    DPRINTF0(("pxtcp_pollout: pxtcp %p\n", (void *)pxtcp));
+
+    if (pxtcp == NULL) {
+        return POLLIN;
+    }
+
+    LWIP_ASSERT1(pxtcp->pmhdl.data == (void *)pxtcp);
+    LWIP_ASSERT1(pxtcp->pmhdl.slot > 0);
+
+    pxtcp->events |= POLLOUT;
+    pollmgr_update_events(pxtcp->pmhdl.slot, pxtcp->events);
+
+    return POLLIN;
+}
+
+
+/**
+ * POLLMGR_CHAN_PXTCP_POLLIN handler.
+ */
+static int
+pxtcp_pmgr_chan_pollin(struct pollmgr_handler *handler, SOCKET fd, int revents)
+{
+    struct pxtcp *pxtcp;
+
+    pxtcp = pxtcp_chan_recv_strong(handler, fd, revents);
+    DPRINTF2(("pxtcp_pollin: pxtcp %p\n", (void *)pxtcp));
+
+    if (pxtcp == NULL) {
+        return POLLIN;
+    }
+
+    LWIP_ASSERT1(pxtcp->pmhdl.data == (void *)pxtcp);
+    LWIP_ASSERT1(pxtcp->pmhdl.slot > 0);
+
+    if (pxtcp->inbound_close) {
+        return POLLIN;
+    }
+
+    pxtcp->events |= POLLIN;
+    pollmgr_update_events(pxtcp->pmhdl.slot, pxtcp->events);
+
+    return POLLIN;
+}
+
+
+#if !(HAVE_TCP_POLLHUP & POLLOUT)
+/**
+ * POLLMGR_CHAN_PXTCP_DEL handler.
+ *
+ * Schedule pxtcp deletion.  We only need this if host system doesn't
+ * report POLLHUP for fully closed tcp sockets.
+ */
+static int
+pxtcp_pmgr_chan_del(struct pollmgr_handler *handler, SOCKET fd, int revents)
+{
+    struct pxtcp *pxtcp;
+
+    pxtcp = pxtcp_chan_recv_strong(handler, fd, revents);
+    if (pxtcp == NULL) {
+        return POLLIN;
+    }
+
+    DPRINTF(("PXTCP_DEL: pxtcp %p; pcb %p; sock %d\n",
+             (void *)pxtcp, (void *)pxtcp->pcb, pxtcp->sock));
+
+    LWIP_ASSERT1(pxtcp->pmhdl.callback != NULL);
+    LWIP_ASSERT1(pxtcp->pmhdl.data == (void *)pxtcp);
+
+    LWIP_ASSERT1(pxtcp->inbound_close);       /* EOF read */
+    LWIP_ASSERT1(pxtcp->outbound_close_done); /* EOF sent */
+
+    pxtcp_pmgr_del(pxtcp);
+    (void) pxtcp_schedule_delete(pxtcp);
+
+    return POLLIN;
+}
+#endif  /* !(HAVE_TCP_POLLHUP & POLLOUT)  */
+
+
+/**
+ * POLLMGR_CHAN_PXTCP_RESET handler.
+ *
+ * Close the socket with RST and delete pxtcp.
+ */
+static int
+pxtcp_pmgr_chan_reset(struct pollmgr_handler *handler, SOCKET fd, int revents)
+{
+    struct pxtcp *pxtcp;
+
+    pxtcp = pxtcp_chan_recv_strong(handler, fd, revents);
+    if (pxtcp == NULL) {
+        return POLLIN;
+    }
+
+    DPRINTF0(("PXTCP_RESET: pxtcp %p; pcb %p; sock %d\n",
+              (void *)pxtcp, (void *)pxtcp->pcb, pxtcp->sock));
+
+    LWIP_ASSERT1(pxtcp->pmhdl.callback != NULL);
+    LWIP_ASSERT1(pxtcp->pmhdl.data == (void *)pxtcp);
+
+    pxtcp_pmgr_del(pxtcp);
+
+    proxy_reset_socket(pxtcp->sock);
+    pxtcp->sock = INVALID_SOCKET;
+
+    (void) pxtcp_schedule_reset(pxtcp);
+
+    return POLLIN;
+}
+
+
+static struct pxtcp *
+pxtcp_allocate(void)
+{
+    struct pxtcp *pxtcp;
+
+    pxtcp = (struct pxtcp *)malloc(sizeof(*pxtcp));
+    if (pxtcp == NULL) {
+        return NULL;
+    }
+
+    pxtcp->pmhdl.callback = NULL;
+    pxtcp->pmhdl.data = (void *)pxtcp;
+    pxtcp->pmhdl.slot = -1;
+
+    pxtcp->pcb = NULL;
+    pxtcp->sock = INVALID_SOCKET;
+    pxtcp->events = 0;
+    pxtcp->sockerr = 0;
+    pxtcp->netif = NULL;
+    pxtcp->unsent = NULL;
+    pxtcp->outbound_close = 0;
+    pxtcp->outbound_close_done = 0;
+    pxtcp->inbound_close = 0;
+    pxtcp->inbound_close_done = 0;
+    pxtcp->inbound_pull = 0;
+    pxtcp->deferred_delete = 0;
+
+    pxtcp->inbuf.bufsize = 64 * 1024;
+    pxtcp->inbuf.buf = (char *)malloc(pxtcp->inbuf.bufsize);
+    if (pxtcp->inbuf.buf == NULL) {
+        free(pxtcp);
+        return NULL;
+    }
+    pxtcp->inbuf.vacant = 0;
+    pxtcp->inbuf.unacked = 0;
+    pxtcp->inbuf.unsent = 0;
+
+    pxtcp->rp = pollmgr_refptr_create(&pxtcp->pmhdl);
+    if (pxtcp->rp == NULL) {
+        free(pxtcp->inbuf.buf);
+        free(pxtcp);
+        return NULL;
+    }
+
+#define CALLBACK_MSG(MSG, FUNC)                         \
+    do {                                                \
+        pxtcp->MSG.type = TCPIP_MSG_CALLBACK_STATIC;    \
+        pxtcp->MSG.sem = NULL;                          \
+        pxtcp->MSG.msg.cb.function = FUNC;              \
+        pxtcp->MSG.msg.cb.ctx = (void *)pxtcp;          \
+    } while (0)
+
+    CALLBACK_MSG(msg_delete, pxtcp_pcb_delete_pxtcp);
+    CALLBACK_MSG(msg_reset, pxtcp_pcb_reset_pxtcp);
+    CALLBACK_MSG(msg_accept, pxtcp_pcb_accept_confirm);
+    CALLBACK_MSG(msg_outbound, pxtcp_pcb_write_outbound);
+    CALLBACK_MSG(msg_inbound, pxtcp_pcb_write_inbound);
+#if HAVE_TCP_POLLHUP
+    CALLBACK_MSG(msg_inpull, pxtcp_pcb_pull_inbound);
+#endif
+
+#undef CALLBACK_MSG
+
+    return pxtcp;
+}
+
+
+/**
+ * Exported to fwtcp to create pxtcp for incoming port-forwarded
+ * connections.  Completed with pcb in pxtcp_pcb_connect().
+ */
+struct pxtcp *
+pxtcp_create_forwarded(SOCKET sock)
+{
+    struct pxtcp *pxtcp;
+
+    pxtcp = pxtcp_allocate();
+    if (pxtcp == NULL) {
+        return NULL;
+    }
+
+    pxtcp->sock = sock;
+    pxtcp->pmhdl.callback = pxtcp_pmgr_pump;
+    pxtcp->events = 0;
+
+    return pxtcp;
+}
+
+
+static void
+pxtcp_pcb_associate(struct pxtcp *pxtcp, struct tcp_pcb *pcb)
+{
+    LWIP_ASSERT1(pxtcp != NULL);
+    LWIP_ASSERT1(pcb != NULL);
+
+    pxtcp->pcb = pcb;
+
+    tcp_arg(pcb, pxtcp);
+
+    tcp_recv(pcb, pxtcp_pcb_recv);
+    tcp_sent(pcb, pxtcp_pcb_sent);
+    tcp_poll(pcb, NULL, 255);
+    tcp_err(pcb, pxtcp_pcb_err);
+}
+
+
+static void
+pxtcp_free(struct pxtcp *pxtcp)
+{
+    if (pxtcp->unsent != NULL) {
+        pbuf_free(pxtcp->unsent);
+    }
+    if (pxtcp->inbuf.buf != NULL) {
+        free(pxtcp->inbuf.buf);
+    }
+    free(pxtcp);
+}
+
+
+/**
+ * Counterpart to pxtcp_create_forwarded() to destruct pxtcp that
+ * fwtcp failed to register with poll manager to post to lwip thread
+ * for doing connect.
+ */
+void
+pxtcp_cancel_forwarded(struct pxtcp *pxtcp)
+{
+    LWIP_ASSERT1(pxtcp->pcb == NULL);
+    pxtcp_pcb_reset_pxtcp(pxtcp);
+}
+
+
+static void
+pxtcp_pcb_dissociate(struct pxtcp *pxtcp)
+{
+    if (pxtcp == NULL || pxtcp->pcb == NULL) {
+        return;
+    }
+
+    DPRINTF(("%s: pxtcp %p <-> pcb %p\n",
+             __func__, (void *)pxtcp, (void *)pxtcp->pcb));
+
+    /*
+     * We must have dissociated from a fully closed pcb immediately
+     * since lwip recycles them and we don't wan't to mess with what
+     * would be someone else's pcb that we happen to have a stale
+     * pointer to.
+     */
+    LWIP_ASSERT1(pxtcp->pcb->callback_arg == pxtcp);
+
+    tcp_recv(pxtcp->pcb, NULL);
+    tcp_sent(pxtcp->pcb, NULL);
+    tcp_poll(pxtcp->pcb, NULL, 255);
+    tcp_err(pxtcp->pcb, NULL);
+    tcp_arg(pxtcp->pcb, NULL);
+    pxtcp->pcb = NULL;
+}
+
+
+/**
+ * Lwip thread callback invoked via pxtcp::msg_delete
+ *
+ * Since we use static messages to communicate to the lwip thread, we
+ * cannot delete pxtcp without making sure there are no unprocessed
+ * messages in the lwip thread mailbox.
+ *
+ * The easiest way to ensure that is to send this "delete" message as
+ * the last one and when it's processed we know there are no more and
+ * it's safe to delete pxtcp.
+ *
+ * Poll manager handlers should use pxtcp_schedule_delete()
+ * convenience function.
+ */
+static void
+pxtcp_pcb_delete_pxtcp(void *ctx)
+{
+    struct pxtcp *pxtcp = (struct pxtcp *)ctx;
+
+    DPRINTF(("%s: pxtcp %p, pcb %p, sock %d%s\n",
+             __func__, (void *)pxtcp, (void *)pxtcp->pcb, pxtcp->sock,
+             (pxtcp->deferred_delete && !pxtcp->inbound_pull
+                  ? " (was deferred)" : "")));
+
+    LWIP_ASSERT1(pxtcp != NULL);
+    LWIP_ASSERT1(pxtcp->pmhdl.slot < 0);
+    LWIP_ASSERT1(pxtcp->outbound_close_done);
+    LWIP_ASSERT1(pxtcp->inbound_close); /* not necessarily done */
+
+
+    /*
+     * pxtcp is no longer registered with poll manager, so it's safe
+     * to close the socket.
+     */
+    if (pxtcp->sock != INVALID_SOCKET) {
+        closesocket(pxtcp->sock);
+        pxtcp->sock = INVALID_SOCKET;
+    }
+
+    /*
+     * We might have already dissociated from a fully closed pcb, or
+     * guest might have sent us a reset while msg_delete was in
+     * transit.  If there's no pcb, we are done.
+     */
+    if (pxtcp->pcb == NULL) {
+        pollmgr_refptr_unref(pxtcp->rp);
+        pxtcp_free(pxtcp);
+        return;
+    }
+
+    /*
+     * Have we completely forwarded all inbound traffic to the guest?
+     *
+     * We may still be waiting for ACKs.  We may have failed to send
+     * some of the data (tcp_write() failed with ERR_MEM).  We may
+     * have failed to send the FIN (tcp_shutdown() failed with
+     * ERR_MEM).
+     */
+    if (pxtcp_pcb_forward_inbound_done(pxtcp)) {
+        pxtcp_pcb_dissociate(pxtcp);
+        pollmgr_refptr_unref(pxtcp->rp);
+        pxtcp_free(pxtcp);
+    }
+    else {
+        DPRINTF2(("delete: pxtcp %p; pcb %p:"
+                  " unacked %d, unsent %d, vacant %d, %s - DEFER!\n",
+                  (void *)pxtcp, (void *)pxtcp->pcb,
+                  (int)pxtcp->inbuf.unacked,
+                  (int)pxtcp->inbuf.unsent,
+                  (int)pxtcp->inbuf.vacant,
+                  pxtcp->inbound_close_done ? "FIN sent" : "FIN is NOT sent"));
+
+        LWIP_ASSERT1(!pxtcp->deferred_delete);
+        pxtcp->deferred_delete = 1;
+    }
+}
+
+
+/**
+ * If we couldn't delete pxtcp right away in the msg_delete callback
+ * from the poll manager thread, we repeat the check at the end of
+ * relevant pcb callbacks.
+ */
+DECLINLINE(void)
+pxtcp_pcb_maybe_deferred_delete(struct pxtcp *pxtcp)
+{
+    if (pxtcp->deferred_delete && pxtcp_pcb_forward_inbound_done(pxtcp)) {
+        pxtcp_pcb_delete_pxtcp(pxtcp);
+    }
+}
+
+
+/**
+ * Poll manager callbacks should use this convenience wrapper to
+ * schedule pxtcp deletion on the lwip thread and to deregister from
+ * the poll manager.
+ */
+static int
+pxtcp_schedule_delete(struct pxtcp *pxtcp)
+{
+    /*
+     * If pollmgr_refptr_get() is called by any channel before
+     * scheduled deletion happens, let them know we are gone.
+     */
+    pxtcp->pmhdl.slot = -1;
+
+    /*
+     * Schedule deletion.  Since poll manager thread may be pre-empted
+     * right after we send the message, the deletion may actually
+     * happen on the lwip thread before we return from this function,
+     * so it's not safe to refer to pxtcp after this call.
+     */
+    proxy_lwip_post(&pxtcp->msg_delete);
+
+    /* tell poll manager to deregister us */
+    return -1;
+}
+
+
+/**
+ * Lwip thread callback invoked via pxtcp::msg_reset
+ *
+ * Like pxtcp_pcb_delete(), but sends RST to the guest before
+ * deleting this pxtcp.
+ */
+static void
+pxtcp_pcb_reset_pxtcp(void *ctx)
+{
+    struct pxtcp *pxtcp = (struct pxtcp *)ctx;
+    LWIP_ASSERT1(pxtcp != NULL);
+
+    DPRINTF0(("%s: pxtcp %p, pcb %p, sock %d\n",
+              __func__, (void *)pxtcp, (void *)pxtcp->pcb, pxtcp->sock));
+
+    if (pxtcp->sock != INVALID_SOCKET) {
+        proxy_reset_socket(pxtcp->sock);
+        pxtcp->sock = INVALID_SOCKET;
+    }
+
+    if (pxtcp->pcb != NULL) {
+        struct tcp_pcb *pcb = pxtcp->pcb;
+        pxtcp_pcb_dissociate(pxtcp);
+        tcp_abort(pcb);
+    }
+
+    pollmgr_refptr_unref(pxtcp->rp);
+    pxtcp_free(pxtcp);
+}
+
+
+
+/**
+ * Poll manager callbacks should use this convenience wrapper to
+ * schedule pxtcp reset and deletion on the lwip thread and to
+ * deregister from the poll manager.
+ *
+ * See pxtcp_schedule_delete() for additional comments.
+ */
+static int
+pxtcp_schedule_reset(struct pxtcp *pxtcp)
+{
+    pxtcp->pmhdl.slot = -1;
+    proxy_lwip_post(&pxtcp->msg_reset);
+    return -1;
+}
+
+
+/**
+ * Reject proxy connection attempt.  Depending on the cause (sockerr)
+ * we may just drop the pcb silently, generate an ICMP datagram or
+ * send TCP reset.
+ */
+static void
+pxtcp_pcb_reject(struct tcp_pcb *pcb, int sockerr,
+                 struct netif *netif,  struct pbuf *p)
+{
+    int reset = 0;
+
+    if (sockerr == ECONNREFUSED) {
+        reset = 1;
+    }
+    else if (p != NULL) {
+        struct netif *oif;
+
+        LWIP_ASSERT1(netif != NULL);
+
+        oif = ip_current_netif();
+        ip_current_netif() = netif;
+
+        if (PCB_ISIPV6(pcb)) {
+            if (sockerr == EHOSTDOWN) {
+                icmp6_dest_unreach(p, ICMP6_DUR_ADDRESS); /* XXX: ??? */
+            }
+            else if (sockerr == EHOSTUNREACH
+                     || sockerr == ENETDOWN
+                     || sockerr == ENETUNREACH)
+            {
+                icmp6_dest_unreach(p, ICMP6_DUR_NO_ROUTE);
+            }
+        }
+        else {
+            if (sockerr == EHOSTDOWN
+                || sockerr == EHOSTUNREACH
+                || sockerr == ENETDOWN
+                || sockerr == ENETUNREACH)
+            {
+                icmp_dest_unreach(p, ICMP_DUR_HOST);
+            }
+        }
+
+        ip_current_netif() = oif;
+    }
+
+    tcp_abandon(pcb, reset);
+}
+
+
+/**
+ * Called from poll manager thread via pxtcp::msg_accept when proxy
+ * failed to connect to the destination.  Also called when we failed
+ * to register pxtcp with poll manager.
+ *
+ * This is like pxtcp_pcb_reset_pxtcp() but is more discriminate in
+ * how this unestablished connection is terminated.
+ */
+static void
+pxtcp_pcb_accept_refuse(void *ctx)
+{
+    struct pxtcp *pxtcp = (struct pxtcp *)ctx;
+
+    DPRINTF0(("%s: pxtcp %p, pcb %p, sock %d: %R[sockerr]\n",
+              __func__, (void *)pxtcp, (void *)pxtcp->pcb,
+              pxtcp->sock, pxtcp->sockerr));
+
+    LWIP_ASSERT1(pxtcp != NULL);
+    LWIP_ASSERT1(pxtcp->sock == INVALID_SOCKET);
+
+    if (pxtcp->pcb != NULL) {
+        struct tcp_pcb *pcb = pxtcp->pcb;
+        pxtcp_pcb_dissociate(pxtcp);
+        pxtcp_pcb_reject(pcb,  pxtcp->sockerr, pxtcp->netif, pxtcp->unsent);
+    }
+
+    pollmgr_refptr_unref(pxtcp->rp);
+    pxtcp_free(pxtcp);
+}
+
+
+/**
+ * Convenience wrapper for poll manager connect callback to reject
+ * connection attempt.
+ *
+ * Like pxtcp_schedule_reset(), but the callback is more discriminate
+ * in how this unestablished connection is terminated.
+ */
+static int
+pxtcp_schedule_reject(struct pxtcp *pxtcp)
+{
+    pxtcp->msg_accept.msg.cb.function = pxtcp_pcb_accept_refuse;
+    pxtcp->pmhdl.slot = -1;
+    proxy_lwip_post(&pxtcp->msg_accept);
+    return -1;
+}
+
+
+/**
+ * Global tcp_proxy_accept() callback for proxied outgoing TCP
+ * connections from guest(s).
+ */
+static err_t
+pxtcp_pcb_heard(void *arg, struct tcp_pcb *newpcb, struct pbuf *syn)
+{
+    LWIP_UNUSED_ARG(arg);
+
+    return pxtcp_pcb_accept_outbound(newpcb, syn,
+               PCB_ISIPV6(newpcb), &newpcb->local_ip, newpcb->local_port);
+}
+
+
+err_t
+pxtcp_pcb_accept_outbound(struct tcp_pcb *newpcb, struct pbuf *p,
+                          int is_ipv6, ipX_addr_t *dst_addr, u16_t dst_port)
+{
+    struct pxtcp *pxtcp;
+    ipX_addr_t mapped_dst_addr;
+    int sdom;
+    SOCKET sock;
+    ssize_t nsent;
+    int sockerr = 0;
+
+    /*
+     * TCP first calls accept callback when it receives the first SYN
+     * and "tentatively accepts" new proxied connection attempt.  When
+     * proxy "confirms" the SYN and sends SYN|ACK and the guest
+     * replies with ACK the accept callback is called again, this time
+     * with the established connection.
+     */
+    LWIP_ASSERT1(newpcb->state == SYN_RCVD_0);
+    tcp_accept(newpcb, pxtcp_pcb_accept);
+    tcp_arg(newpcb, NULL);
+
+    tcp_setprio(newpcb, TCP_PRIO_MAX);
+
+    pxremap_outbound_ipX(is_ipv6, &mapped_dst_addr, dst_addr);
+
+    sdom = is_ipv6 ? PF_INET6 : PF_INET;
+    sock = proxy_connected_socket(sdom, SOCK_STREAM,
+                                  &mapped_dst_addr, dst_port);
+    if (sock == INVALID_SOCKET) {
+        sockerr = SOCKERRNO();
+        goto abort;
+    }
+
+    pxtcp = pxtcp_allocate();
+    if (pxtcp == NULL) {
+        proxy_reset_socket(sock);
+        goto abort;
+    }
+
+    /* save initial datagram in case we need to reply with ICMP */
+    if (p != NULL) {
+        pbuf_ref(p);
+        pxtcp->unsent = p;
+        pxtcp->netif = ip_current_netif();
+    }
+
+    pxtcp_pcb_associate(pxtcp, newpcb);
+    pxtcp->sock = sock;
+
+    pxtcp->pmhdl.callback = pxtcp_pmgr_connect;
+    pxtcp->events = POLLOUT;
+
+    nsent = pxtcp_chan_send(POLLMGR_CHAN_PXTCP_ADD, pxtcp);
+    if (nsent < 0) {
+        pxtcp->sock = INVALID_SOCKET;
+        proxy_reset_socket(sock);
+        pxtcp_pcb_accept_refuse(pxtcp);
+        return ERR_ABRT;
+    }
+
+    return ERR_OK;
+
+  abort:
+    DPRINTF0(("%s: pcb %p, sock %d: %R[sockerr]\n",
+              __func__, (void *)newpcb, sock, sockerr));
+    pxtcp_pcb_reject(newpcb, sockerr, ip_current_netif(), p);
+    return ERR_ABRT;
+}
+
+
+/**
+ * tcp_proxy_accept() callback for accepted proxied outgoing TCP
+ * connections from guest(s).  This is "real" accept with three-way
+ * handshake completed.
+ */
+static err_t
+pxtcp_pcb_accept(void *arg, struct tcp_pcb *pcb, err_t error)
+{
+    struct pxtcp *pxtcp = (struct pxtcp *)arg;
+
+    LWIP_UNUSED_ARG(pcb);       /* used only in asserts */
+    LWIP_UNUSED_ARG(error);     /* always ERR_OK */
+
+    LWIP_ASSERT1(pxtcp != NULL);
+    LWIP_ASSERT1(pxtcp->pcb = pcb);
+    LWIP_ASSERT1(pcb->callback_arg == pxtcp);
+
+    /* send any inbound data that are already queued */
+    pxtcp_pcb_forward_inbound(pxtcp);
+    return ERR_OK;
+}
+
+
+/**
+ * Initial poll manager callback for proxied outgoing TCP connections.
+ * pxtcp_pcb_accept() sets pxtcp::pmhdl::callback to this.
+ *
+ * Waits for connect(2) to the destination to complete.  On success
+ * replaces itself with pxtcp_pmgr_pump() callback common to all
+ * established TCP connections.
+ */
+static int
+pxtcp_pmgr_connect(struct pollmgr_handler *handler, SOCKET fd, int revents)
+{
+    struct pxtcp *pxtcp;
+    RT_NOREF(fd);
+
+    pxtcp = (struct pxtcp *)handler->data;
+    LWIP_ASSERT1(handler == &pxtcp->pmhdl);
+    LWIP_ASSERT1(fd == pxtcp->sock);
+    LWIP_ASSERT1(pxtcp->sockerr == 0);
+
+    if (revents & POLLNVAL) {
+        pxtcp->sock = INVALID_SOCKET;
+        pxtcp->sockerr = ETIMEDOUT;
+        return pxtcp_schedule_reject(pxtcp);
+    }
+
+    /*
+     * Solaris and NetBSD don't report either POLLERR or POLLHUP when
+     * connect(2) fails, just POLLOUT.  In that case we always need to
+     * check SO_ERROR.
+     */
+#if defined(RT_OS_SOLARIS) || defined(RT_OS_NETBSD)
+# define CONNECT_CHECK_ERROR POLLOUT
+#else
+# define CONNECT_CHECK_ERROR (POLLERR | POLLHUP)
+#endif
+
+    /*
+     * Check the cause of the failure so that pxtcp_pcb_reject() may
+     * behave accordingly.
+     */
+    if (revents & CONNECT_CHECK_ERROR) {
+        socklen_t optlen = (socklen_t)sizeof(pxtcp->sockerr);
+        int status;
+        SOCKET s;
+
+        status = getsockopt(pxtcp->sock, SOL_SOCKET, SO_ERROR,
+                            (char *)&pxtcp->sockerr, &optlen);
+        if (RT_UNLIKELY(status == SOCKET_ERROR)) { /* should not happen */
+            DPRINTF(("%s: sock %d: SO_ERROR failed: %R[sockerr]\n",
+                     __func__, fd, SOCKERRNO()));
+            pxtcp->sockerr = ETIMEDOUT;
+        }
+        else {
+            /* don't spam this log on successful connect(2) */
+            if ((revents & (POLLERR | POLLHUP)) /* we were told it's failed */
+                || pxtcp->sockerr != 0)         /* we determined it's failed */
+            {
+                DPRINTF(("%s: sock %d: connect: %R[sockerr]\n",
+                         __func__, fd, pxtcp->sockerr));
+            }
+
+            if ((revents & (POLLERR | POLLHUP))
+                && RT_UNLIKELY(pxtcp->sockerr == 0))
+            {
+                /* if we're told it's failed, make sure it's marked as such */
+                pxtcp->sockerr = ETIMEDOUT;
+            }
+        }
+
+        if (pxtcp->sockerr != 0) {
+            s = pxtcp->sock;
+            pxtcp->sock = INVALID_SOCKET;
+            closesocket(s);
+            return pxtcp_schedule_reject(pxtcp);
+        }
+    }
+
+    if (revents & POLLOUT) { /* connect is successful */
+        /* confirm accept to the guest */
+        proxy_lwip_post(&pxtcp->msg_accept);
+
+        /*
+         * Switch to common callback used for all established proxied
+         * connections.
+         */
+        pxtcp->pmhdl.callback = pxtcp_pmgr_pump;
+
+        /*
+         * Initially we poll for incoming traffic only.  Outgoing
+         * traffic is fast-forwarded by pxtcp_pcb_recv(); if it fails
+         * it will ask us to poll for POLLOUT too.
+         */
+        pxtcp->events = POLLIN;
+        return pxtcp->events;
+    }
+
+    /* should never get here */
+    DPRINTF0(("%s: pxtcp %p, sock %d: unexpected revents 0x%x\n",
+              __func__, (void *)pxtcp, fd, revents));
+    return pxtcp_schedule_reset(pxtcp);
+}
+
+
+/**
+ * Called from poll manager thread via pxtcp::msg_accept when proxy
+ * connected to the destination.  Finalize accept by sending SYN|ACK
+ * to the guest.
+ */
+static void
+pxtcp_pcb_accept_confirm(void *ctx)
+{
+    struct pxtcp *pxtcp = (struct pxtcp *)ctx;
+    err_t error;
+
+    LWIP_ASSERT1(pxtcp != NULL);
+    if (pxtcp->pcb == NULL) {
+        return;
+    }
+
+    /* we are not going to reply with ICMP, so we can drop initial pbuf */
+    if (pxtcp->unsent != NULL) {
+        pbuf_free(pxtcp->unsent);
+        pxtcp->unsent = NULL;
+    }
+
+    error = tcp_proxy_accept_confirm(pxtcp->pcb);
+
+    /*
+     * If lwIP failed to enqueue SYN|ACK because it's out of pbufs it
+     * abandons the pcb.  Retrying that is not very easy, since it
+     * would require keeping "fractional state".  From guest's point
+     * of view there is no reply to its SYN so it will either resend
+     * the SYN (effetively triggering full connection retry for us),
+     * or it will eventually time out.
+     */
+    if (error == ERR_ABRT) {
+        pxtcp->pcb = NULL;      /* pcb is gone */
+        pxtcp_chan_send_weak(POLLMGR_CHAN_PXTCP_RESET, pxtcp);
+    }
+
+    /*
+     * else if (error != ERR_OK): even if tcp_output() failed with
+     * ERR_MEM - don't give up, that SYN|ACK is enqueued and will be
+     * retransmitted eventually.
+     */
+}
+
+
+/**
+ * Entry point for port-forwarding.
+ *
+ * fwtcp accepts new incoming connection, creates pxtcp for the socket
+ * (with no pcb yet) and adds it to the poll manager (polling for
+ * errors only).  Then it calls this function to construct the pcb and
+ * perform connection to the guest.
+ */
+void
+pxtcp_pcb_connect(struct pxtcp *pxtcp, const struct fwspec *fwspec)
+{
+    struct sockaddr_storage ss;
+    socklen_t sslen;
+    struct tcp_pcb *pcb;
+    ipX_addr_t src_addr, dst_addr;
+    u16_t src_port, dst_port;
+    int status;
+    err_t error;
+
+    LWIP_ASSERT1(pxtcp != NULL);
+    LWIP_ASSERT1(pxtcp->pcb == NULL);
+    LWIP_ASSERT1(fwspec->stype == SOCK_STREAM);
+
+    pcb = tcp_new();
+    if (pcb == NULL) {
+        goto reset;
+    }
+
+    tcp_setprio(pcb, TCP_PRIO_MAX);
+    pxtcp_pcb_associate(pxtcp, pcb);
+
+    sslen = sizeof(ss);
+    status = getpeername(pxtcp->sock, (struct sockaddr *)&ss, &sslen);
+    if (status  == SOCKET_ERROR) {
+        goto reset;
+    }
+
+    /* nit: compares PF and AF, but they are the same everywhere */
+    LWIP_ASSERT1(ss.ss_family == fwspec->sdom);
+
+    status = fwany_ipX_addr_set_src(&src_addr, (const struct sockaddr *)&ss);
+    if (status == PXREMAP_FAILED) {
+        goto reset;
+    }
+
+    if (ss.ss_family == PF_INET) {
+        const struct sockaddr_in *peer4 = (const struct sockaddr_in *)&ss;
+
+        src_port = peer4->sin_port;
+
+        memcpy(&dst_addr.ip4, &fwspec->dst.sin.sin_addr, sizeof(ip_addr_t));
+        dst_port = fwspec->dst.sin.sin_port;
+    }
+    else { /* PF_INET6 */
+        const struct sockaddr_in6 *peer6 = (const struct sockaddr_in6 *)&ss;
+        ip_set_v6(pcb, 1);
+
+        src_port = peer6->sin6_port;
+
+        memcpy(&dst_addr.ip6, &fwspec->dst.sin6.sin6_addr, sizeof(ip6_addr_t));
+        dst_port = fwspec->dst.sin6.sin6_port;
+    }
+
+    /* lwip port arguments are in host order */
+    src_port = ntohs(src_port);
+    dst_port = ntohs(dst_port);
+
+    error = tcp_proxy_bind(pcb, ipX_2_ip(&src_addr), src_port);
+    if (error != ERR_OK) {
+        goto reset;
+    }
+
+    error = tcp_connect(pcb, ipX_2_ip(&dst_addr), dst_port,
+                        /* callback: */ pxtcp_pcb_connected);
+    if (error != ERR_OK) {
+        goto reset;
+    }
+
+    return;
+
+  reset:
+    pxtcp_chan_send_weak(POLLMGR_CHAN_PXTCP_RESET, pxtcp);
+}
+
+
+/**
+ * Port-forwarded connection to guest is successful, pump data.
+ */
+static err_t
+pxtcp_pcb_connected(void *arg, struct tcp_pcb *pcb, err_t error)
+{
+    struct pxtcp *pxtcp = (struct pxtcp *)arg;
+
+    LWIP_ASSERT1(error == ERR_OK); /* always called with ERR_OK */
+    LWIP_UNUSED_ARG(error);
+
+    LWIP_ASSERT1(pxtcp != NULL);
+    LWIP_ASSERT1(pxtcp->pcb == pcb);
+    LWIP_ASSERT1(pcb->callback_arg == pxtcp);
+    LWIP_UNUSED_ARG(pcb);
+
+    DPRINTF0(("%s: new pxtcp %p; pcb %p; sock %d\n",
+              __func__, (void *)pxtcp, (void *)pxtcp->pcb, pxtcp->sock));
+
+    /* ACK on connection is like ACK on data in pxtcp_pcb_sent() */
+    pxtcp_chan_send_weak(POLLMGR_CHAN_PXTCP_POLLIN, pxtcp);
+
+    return ERR_OK;
+}
+
+
+/**
+ * tcp_recv() callback.
+ */
+static err_t
+pxtcp_pcb_recv(void *arg, struct tcp_pcb *pcb, struct pbuf *p, err_t error)
+{
+    struct pxtcp *pxtcp = (struct pxtcp *)arg;
+
+    LWIP_ASSERT1(error == ERR_OK); /* always called with ERR_OK */
+    LWIP_UNUSED_ARG(error);
+
+    LWIP_ASSERT1(pxtcp != NULL);
+    LWIP_ASSERT1(pxtcp->pcb == pcb);
+    LWIP_ASSERT1(pcb->callback_arg == pxtcp);
+    LWIP_UNUSED_ARG(pcb);
+
+
+    /*
+     * Have we done sending previous batch?
+     */
+    if (pxtcp->unsent != NULL) {
+        if (p != NULL) {
+            /*
+             * Return an error to tell TCP to hold onto that pbuf.
+             * It will be presented to us later from tcp_fasttmr().
+             */
+            return ERR_WOULDBLOCK;
+        }
+        else {
+            /*
+             * Unlike data, p == NULL indicating orderly shutdown is
+             * NOT presented to us again
+             */
+            pxtcp->outbound_close = 1;
+            return ERR_OK;
+        }
+    }
+
+
+    /*
+     * Guest closed?
+     */
+    if (p == NULL) {
+        pxtcp->outbound_close = 1;
+        pxtcp_pcb_forward_outbound_close(pxtcp);
+        return ERR_OK;
+    }
+
+
+    /*
+     * Got data, send what we can without blocking.
+     */
+    return pxtcp_pcb_forward_outbound(pxtcp, p);
+}
+
+
+/**
+ * Guest half-closed its TX side of the connection.
+ *
+ * Called either immediately from pxtcp_pcb_recv() when it gets NULL,
+ * or from pxtcp_pcb_forward_outbound() when it finishes forwarding
+ * previously unsent data and sees pxtcp::outbound_close flag saved by
+ * pxtcp_pcb_recv().
+ */
+static void
+pxtcp_pcb_forward_outbound_close(struct pxtcp *pxtcp)
+{
+    struct tcp_pcb *pcb;
+
+    LWIP_ASSERT1(pxtcp != NULL);
+    LWIP_ASSERT1(pxtcp->outbound_close);
+    LWIP_ASSERT1(!pxtcp->outbound_close_done);
+
+    pcb = pxtcp->pcb;
+    LWIP_ASSERT1(pcb != NULL);
+
+    DPRINTF(("outbound_close: pxtcp %p; pcb %p %s\n",
+             (void *)pxtcp, (void *)pcb, tcp_debug_state_str(pcb->state)));
+
+
+    /* set the flag first, since shutdown() may trigger POLLHUP */
+    pxtcp->outbound_close_done = 1;
+    shutdown(pxtcp->sock, SHUT_WR); /* half-close the socket */
+
+#if !(HAVE_TCP_POLLHUP & POLLOUT)
+    /*
+     * We need to nudge poll manager manually, since OS will not
+     * report POLLHUP.
+     */
+    if (pxtcp->inbound_close) {
+        pxtcp_chan_send_weak(POLLMGR_CHAN_PXTCP_DEL, pxtcp);
+    }
+#endif
+
+
+    /* no more outbound data coming to us */
+    tcp_recv(pcb, NULL);
+
+    /*
+     * If we have already done inbound close previously (active close
+     * on the pcb), then we must not hold onto a pcb in TIME_WAIT
+     * state since those will be recycled by lwip when it runs out of
+     * free pcbs in the pool.
+     *
+     * The test is true also for a pcb in CLOSING state that waits
+     * just for the ACK of its FIN (to transition to TIME_WAIT).
+     */
+    if (pxtcp_pcb_forward_inbound_done(pxtcp)) {
+        pxtcp_pcb_dissociate(pxtcp);
+    }
+}
+
+
+/**
+ * Forward outbound data from pcb to socket.
+ *
+ * Called by pxtcp_pcb_recv() to forward new data and by callout
+ * triggered by POLLOUT on the socket to send previously unsent data.
+ *
+ * (Re)scehdules one-time callout if not all data are sent.
+ */
+static err_t
+pxtcp_pcb_forward_outbound(struct pxtcp *pxtcp, struct pbuf *p)
+{
+    struct pbuf *qs, *q;
+    size_t qoff;
+    size_t forwarded;
+    int sockerr;
+
+    LWIP_ASSERT1(pxtcp->unsent == NULL || pxtcp->unsent == p);
+
+    forwarded = 0;
+    sockerr = 0;
+
+    q = NULL;
+    qoff = 0;
+
+    qs = p;
+    while (qs != NULL) {
+        IOVEC iov[8];
+        const size_t iovsize = sizeof(iov)/sizeof(iov[0]);
+        size_t fwd1;
+        ssize_t nsent;
+        size_t i;
+
+        fwd1 = 0;
+        for (i = 0, q = qs; i < iovsize && q != NULL; ++i, q = q->next) {
+            LWIP_ASSERT1(q->len > 0);
+            IOVEC_SET_BASE(iov[i], q->payload);
+            IOVEC_SET_LEN(iov[i], q->len);
+            fwd1 += q->len;
+        }
+
+        /*
+         * TODO: This is where application-level proxy can hook into
+         * to process outbound traffic.
+         */
+        nsent = pxtcp_sock_send(pxtcp, iov, i);
+
+        if (nsent == (ssize_t)fwd1) {
+            /* successfully sent this chain fragment completely */
+            forwarded += nsent;
+            qs = q;
+        }
+        else if (nsent >= 0) {
+            /* successfully sent only some data */
+            forwarded += nsent;
+
+            /* find the first pbuf that was not completely forwarded */
+            qoff = nsent;
+            for (i = 0, q = qs; i < iovsize && q != NULL; ++i, q = q->next) {
+                if (qoff < q->len) {
+                    break;
+                }
+                qoff -= q->len;
+            }
+            LWIP_ASSERT1(q != NULL);
+            LWIP_ASSERT1(qoff < q->len);
+            break;
+        }
+        else {
+            sockerr = -nsent;
+
+            /*
+             * Some errors are really not errors - if we get them,
+             * it's not different from getting nsent == 0, so filter
+             * them out here.
+             */
+            if (proxy_error_is_transient(sockerr)) {
+                sockerr = 0;
+            }
+            q = qs;
+            qoff = 0;
+            break;
+        }
+    }
+
+    if (forwarded > 0) {
+        DPRINTF2(("forward_outbound: pxtcp %p, pcb %p: sent %d bytes\n",
+                  (void *)pxtcp, (void *)pxtcp->pcb, (int)forwarded));
+        tcp_recved(pxtcp->pcb, (u16_t)forwarded);
+    }
+
+    if (q == NULL) { /* everything is forwarded? */
+        LWIP_ASSERT1(sockerr == 0);
+        LWIP_ASSERT1(forwarded == p->tot_len);
+
+        pxtcp->unsent = NULL;
+        pbuf_free(p);
+        if (pxtcp->outbound_close) {
+            pxtcp_pcb_forward_outbound_close(pxtcp);
+        }
+    }
+    else {
+        if (q != p) {
+            /* free forwarded pbufs at the beginning of the chain */
+            pbuf_ref(q);
+            pbuf_free(p);
+        }
+        if (qoff > 0) {
+            /* advance payload pointer past the forwarded part */
+            pbuf_header(q, -(s16_t)qoff);
+        }
+        pxtcp->unsent = q;
+        DPRINTF2(("forward_outbound: pxtcp %p, pcb %p: kept %d bytes\n",
+                  (void *)pxtcp, (void *)pxtcp->pcb, (int)q->tot_len));
+
+        /*
+         * Have sendmsg() failed?
+         *
+         * Connection reset will be detected by poll and
+         * pxtcp_schedule_reset() will be called.
+         *
+         * Otherwise something *really* unexpected must have happened,
+         * so we'd better abort.
+         */
+        if (sockerr != 0 && sockerr != ECONNRESET) {
+            struct tcp_pcb *pcb = pxtcp->pcb;
+            DPRINTF2(("forward_outbound: pxtcp %p, pcb %p: %R[sockerr]\n",
+                      (void *)pxtcp, (void *)pcb, sockerr));
+
+            pxtcp_pcb_dissociate(pxtcp);
+
+            tcp_abort(pcb);
+
+            /* call error callback manually since we've already dissociated */
+            pxtcp_pcb_err((void *)pxtcp, ERR_ABRT);
+            return ERR_ABRT;
+        }
+
+        /* schedule one-shot POLLOUT on the socket */
+        pxtcp_chan_send_weak(POLLMGR_CHAN_PXTCP_POLLOUT, pxtcp);
+    }
+    return ERR_OK;
+}
+
+
+#if !defined(RT_OS_WINDOWS)
+static ssize_t
+pxtcp_sock_send(struct pxtcp *pxtcp, IOVEC *iov, size_t iovlen)
+{
+    struct msghdr mh;
+    ssize_t nsent;
+
+#ifdef MSG_NOSIGNAL
+    const int send_flags = MSG_NOSIGNAL;
+#else
+    const int send_flags = 0;
+#endif
+
+    memset(&mh, 0, sizeof(mh));
+
+    mh.msg_iov = iov;
+    mh.msg_iovlen = iovlen;
+
+    nsent = sendmsg(pxtcp->sock, &mh, send_flags);
+    if (nsent < 0) {
+        nsent = -SOCKERRNO();
+    }
+
+    return nsent;
+}
+#else /* RT_OS_WINDOWS */
+static ssize_t
+pxtcp_sock_send(struct pxtcp *pxtcp, IOVEC *iov, size_t iovlen)
+{
+    DWORD nsent;
+    int status;
+
+    status = WSASend(pxtcp->sock, iov, (DWORD)iovlen, &nsent,
+                     0, NULL, NULL);
+    if (status == SOCKET_ERROR) {
+        return -SOCKERRNO();
+    }
+
+    return nsent;
+}
+#endif /* RT_OS_WINDOWS */
+
+
+/**
+ * Callback from poll manager (on POLLOUT) to send data from
+ * pxtcp::unsent pbuf to socket.
+ */
+static void
+pxtcp_pcb_write_outbound(void *ctx)
+{
+    struct pxtcp *pxtcp = (struct pxtcp *)ctx;
+    LWIP_ASSERT1(pxtcp != NULL);
+
+    if (pxtcp->pcb == NULL) {
+        return;
+    }
+
+    pxtcp_pcb_forward_outbound(pxtcp, pxtcp->unsent);
+}
+
+
+/**
+ * Common poll manager callback used by both outgoing and incoming
+ * (port-forwarded) connections that has connected socket.
+ */
+static int
+pxtcp_pmgr_pump(struct pollmgr_handler *handler, SOCKET fd, int revents)
+{
+    struct pxtcp *pxtcp;
+    int status;
+    int sockerr;
+    RT_NOREF(fd);
+
+    pxtcp = (struct pxtcp *)handler->data;
+    LWIP_ASSERT1(handler == &pxtcp->pmhdl);
+    LWIP_ASSERT1(fd == pxtcp->sock);
+
+    if (revents & POLLNVAL) {
+        pxtcp->sock = INVALID_SOCKET;
+        return pxtcp_schedule_reset(pxtcp);
+    }
+
+    if (revents & POLLERR) {
+        socklen_t optlen = (socklen_t)sizeof(sockerr);
+
+        status = getsockopt(pxtcp->sock, SOL_SOCKET, SO_ERROR,
+                            (char *)&sockerr, &optlen);
+        if (status == SOCKET_ERROR) { /* should not happen */
+            DPRINTF(("sock %d: POLLERR: SO_ERROR failed: %R[sockerr]\n",
+                     fd, SOCKERRNO()));
+        }
+        else {
+            DPRINTF0(("sock %d: POLLERR: %R[sockerr]\n", fd, sockerr));
+        }
+        return pxtcp_schedule_reset(pxtcp);
+    }
+
+    if (revents & POLLOUT) {
+        pxtcp->events &= ~POLLOUT;
+        proxy_lwip_post(&pxtcp->msg_outbound);
+    }
+
+    if (revents & POLLIN) {
+        ssize_t nread;
+        int stop_pollin;
+
+        nread = pxtcp_sock_read(pxtcp, &stop_pollin);
+        if (nread < 0) {
+            sockerr = -(int)nread;
+            DPRINTF0(("sock %d: POLLIN: %R[sockerr]\n", fd, sockerr));
+            return pxtcp_schedule_reset(pxtcp);
+        }
+
+        if (stop_pollin) {
+            pxtcp->events &= ~POLLIN;
+        }
+
+        if (nread > 0) {
+            proxy_lwip_post(&pxtcp->msg_inbound);
+#if !HAVE_TCP_POLLHUP
+            /*
+             * If host does not report POLLHUP for closed sockets
+             * (e.g. NetBSD) we should check for full close manually.
+             */
+            if (pxtcp->inbound_close && pxtcp->outbound_close_done) {
+                LWIP_ASSERT1((revents & POLLHUP) == 0);
+                return pxtcp_schedule_delete(pxtcp);
+            }
+#endif
+        }
+    }
+
+#if !HAVE_TCP_POLLHUP
+    LWIP_ASSERT1((revents & POLLHUP) == 0);
+#else
+    if (revents & POLLHUP) {
+        DPRINTF(("sock %d: HUP\n", fd));
+
+#if HAVE_TCP_POLLHUP == POLLIN
+        /*
+         * XXX: OSX reports POLLHUP once more when inbound is already
+         * half-closed (which has already been reported as a "normal"
+         * POLLHUP, handled below), the socket is polled for POLLOUT
+         * (guest sends a lot of data that we can't push out fast
+         * enough), and remote sends a reset - e.g. an http client
+         * that half-closes after request and then aborts the transfer.
+         *
+         * It really should have been reported as POLLERR, but it
+         * seems OSX never reports POLLERR for sockets.
+         */
+#if defined(RT_OS_DARWIN)
+        {
+            socklen_t optlen = (socklen_t)sizeof(sockerr);
+
+            status = getsockopt(pxtcp->sock, SOL_SOCKET, SO_ERROR,
+                                (char *)&sockerr, &optlen);
+            if (status == SOCKET_ERROR) { /* should not happen */
+                DPRINTF(("sock %d: POLLHUP: SO_ERROR failed: %R[sockerr]\n",
+                         fd, SOCKERRNO()));
+                sockerr = ECONNRESET;
+            }
+            else if (sockerr != 0) {
+                DPRINTF0(("sock %d: POLLHUP: %R[sockerr]\n", fd, sockerr));
+            }
+
+            if (sockerr != 0) { /* XXX: should have been POLLERR */
+                return pxtcp_schedule_reset(pxtcp);
+            }
+        }
+#endif  /* RT_OS_DARWIN */
+
+        /*
+         * Remote closed inbound.
+         */
+        if (!pxtcp->outbound_close_done) {
+            /*
+             * We might still need to poll for POLLOUT, but we can not
+             * poll for POLLIN anymore (even if not all data are read)
+             * because we will be spammed by POLLHUP.
+             */
+            pxtcp->events &= ~POLLIN;
+            if (!pxtcp->inbound_close) {
+                /* the rest of the input has to be pulled */
+                proxy_lwip_post(&pxtcp->msg_inpull);
+            }
+        }
+        else
+#endif
+        /*
+         * Both directions are closed.
+         */
+        {
+            LWIP_ASSERT1(pxtcp->outbound_close_done);
+
+            if (pxtcp->inbound_close) {
+                /* there's no unread data, we are done */
+                return pxtcp_schedule_delete(pxtcp);
+            }
+            else {
+                /* pull the rest of the input first (deferred_delete) */
+                pxtcp->pmhdl.slot = -1;
+                proxy_lwip_post(&pxtcp->msg_inpull);
+                return -1;
+            }
+            /* NOTREACHED */
+        }
+
+    }
+#endif  /* HAVE_TCP_POLLHUP */
+
+    return pxtcp->events;
+}
+
+
+/**
+ * Read data from socket to ringbuf.  This may be used both on lwip
+ * and poll manager threads.
+ *
+ * Flag pointed to by pstop is set when further reading is impossible,
+ * either temporary when buffer is full, or permanently when EOF is
+ * received.
+ *
+ * Returns number of bytes read.  NB: EOF is reported as 1!
+ *
+ * Returns zero if nothing was read, either because buffer is full, or
+ * if no data is available (EWOULDBLOCK, EINTR &c).
+ *
+ * Returns -errno on real socket errors.
+ */
+static ssize_t
+pxtcp_sock_read(struct pxtcp *pxtcp, int *pstop)
+{
+    IOVEC iov[2];
+    size_t iovlen;
+    ssize_t nread;
+
+    const size_t sz = pxtcp->inbuf.bufsize;
+    size_t beg, lim, wrnew;
+
+    *pstop = 0;
+
+    beg = pxtcp->inbuf.vacant;
+    IOVEC_SET_BASE(iov[0], &pxtcp->inbuf.buf[beg]);
+
+    /* lim is the index we can NOT write to */
+    lim = pxtcp->inbuf.unacked;
+    if (lim == 0) {
+        lim = sz - 1;           /* empty slot at the end */
+    }
+    else if (lim == 1 && beg != 0) {
+        lim = sz;               /* empty slot at the beginning */
+    }
+    else {
+        --lim;
+    }
+
+    if (beg == lim) {
+        /*
+         * Buffer is full, stop polling for POLLIN.
+         *
+         * pxtcp_pcb_sent() will re-enable POLLIN when guest ACKs
+         * data, freeing space in the ring buffer.
+         */
+        *pstop = 1;
+        return 0;
+    }
+
+    if (beg < lim) {
+        /* free space in one chunk */
+        iovlen = 1;
+        IOVEC_SET_LEN(iov[0], lim - beg);
+    }
+    else {
+        /* free space in two chunks */
+        iovlen = 2;
+        IOVEC_SET_LEN(iov[0], sz - beg);
+        IOVEC_SET_BASE(iov[1], &pxtcp->inbuf.buf[0]);
+        IOVEC_SET_LEN(iov[1], lim);
+    }
+
+    /*
+     * TODO: This is where application-level proxy can hook into to
+     * process inbound traffic.
+     */
+    nread = pxtcp_sock_recv(pxtcp, iov, iovlen);
+
+    if (nread > 0) {
+        wrnew = beg + nread;
+        if (wrnew >= sz) {
+            wrnew -= sz;
+        }
+        pxtcp->inbuf.vacant = wrnew;
+        DPRINTF2(("pxtcp %p: sock %d read %d bytes\n",
+                  (void *)pxtcp, pxtcp->sock, (int)nread));
+        return nread;
+    }
+    else if (nread == 0) {
+        *pstop = 1;
+        pxtcp->inbound_close = 1;
+        DPRINTF2(("pxtcp %p: sock %d read EOF\n",
+                 (void *)pxtcp, pxtcp->sock));
+        return 1;
+    }
+    else {
+        int sockerr = -nread;
+
+        if (proxy_error_is_transient(sockerr)) {
+            /* haven't read anything, just return */
+            DPRINTF2(("pxtcp %p: sock %d read cancelled\n",
+                      (void *)pxtcp, pxtcp->sock));
+            return 0;
+        }
+        else {
+            /* socket error! */
+            DPRINTF0(("pxtcp %p: sock %d read: %R[sockerr]\n",
+                      (void *)pxtcp, pxtcp->sock, sockerr));
+            return -sockerr;
+        }
+    }
+}
+
+
+#if !defined(RT_OS_WINDOWS)
+static ssize_t
+pxtcp_sock_recv(struct pxtcp *pxtcp, IOVEC *iov, size_t iovlen)
+{
+    struct msghdr mh;
+    ssize_t nread;
+
+    memset(&mh, 0, sizeof(mh));
+
+    mh.msg_iov = iov;
+    mh.msg_iovlen = iovlen;
+
+    nread = recvmsg(pxtcp->sock, &mh, 0);
+    if (nread < 0) {
+        nread = -SOCKERRNO();
+    }
+
+    return nread;
+}
+#else /* RT_OS_WINDOWS */
+static ssize_t
+pxtcp_sock_recv(struct pxtcp *pxtcp, IOVEC *iov, size_t iovlen)
+{
+    DWORD flags;
+    DWORD nread;
+    int status;
+
+    flags = 0;
+    status = WSARecv(pxtcp->sock, iov, (DWORD)iovlen, &nread,
+                     &flags, NULL, NULL);
+    if (status == SOCKET_ERROR) {
+        return -SOCKERRNO();
+    }
+
+    return (ssize_t)nread;
+}
+#endif /* RT_OS_WINDOWS */
+
+
+/**
+ * Callback from poll manager (pxtcp::msg_inbound) to trigger output
+ * from ringbuf to guest.
+ */
+static void
+pxtcp_pcb_write_inbound(void *ctx)
+{
+    struct pxtcp *pxtcp = (struct pxtcp *)ctx;
+    LWIP_ASSERT1(pxtcp != NULL);
+
+    if (pxtcp->pcb == NULL) {
+        return;
+    }
+
+    pxtcp_pcb_forward_inbound(pxtcp);
+}
+
+
+/**
+ * tcp_poll() callback
+ *
+ * We swtich it on when tcp_write() or tcp_shutdown() fail with
+ * ERR_MEM to prevent connection from stalling.  If there are ACKs or
+ * more inbound data then pxtcp_pcb_forward_inbound() will be
+ * triggered again, but if neither happens, tcp_poll() comes to the
+ * rescue.
+ */
+static err_t
+pxtcp_pcb_poll(void *arg, struct tcp_pcb *pcb)
+{
+    struct pxtcp *pxtcp = (struct pxtcp *)arg;
+    LWIP_UNUSED_ARG(pcb);
+
+    DPRINTF2(("%s: pxtcp %p; pcb %p\n",
+              __func__, (void *)pxtcp, (void *)pxtcp->pcb));
+
+    pxtcp_pcb_forward_inbound(pxtcp);
+
+    /*
+     * If the last thing holding up deletion of the pxtcp was failed
+     * tcp_shutdown() and it succeeded, we may be the last callback.
+     */
+    pxtcp_pcb_maybe_deferred_delete(pxtcp);
+
+    return ERR_OK;
+}
+
+
+static void
+pxtcp_pcb_schedule_poll(struct pxtcp *pxtcp)
+{
+    tcp_poll(pxtcp->pcb, pxtcp_pcb_poll, 0);
+}
+
+
+static void
+pxtcp_pcb_cancel_poll(struct pxtcp *pxtcp)
+{
+    tcp_poll(pxtcp->pcb, NULL, 255);
+}
+
+
+/**
+ * Forward inbound data from ring buffer to the guest.
+ *
+ * Scheduled by poll manager thread after it receives more data into
+ * the ring buffer (we have more data to send).
+
+ * Also called from tcp_sent() callback when guest ACKs some data,
+ * increasing pcb->snd_buf (we are permitted to send more data).
+ *
+ * Also called from tcp_poll() callback if previous attempt to forward
+ * inbound data failed with ERR_MEM (we need to try again).
+ */
+static void
+pxtcp_pcb_forward_inbound(struct pxtcp *pxtcp)
+{
+    struct tcp_pcb *pcb;
+    size_t sndbuf;
+    size_t beg, lim, sndlim;
+    size_t toeob, tolim;
+    size_t nsent;
+    err_t error;
+
+    LWIP_ASSERT1(pxtcp != NULL);
+    pcb = pxtcp->pcb;
+    if (pcb == NULL) {
+        return;
+    }
+
+    if (/* __predict_false */ pcb->state < ESTABLISHED) {
+        /*
+         * If we have just confirmed accept of this connection, the
+         * pcb is in SYN_RCVD state and we still haven't received the
+         * ACK of our SYN.  It's only in SYN_RCVD -> ESTABLISHED
+         * transition that lwip decrements pcb->acked so that that ACK
+         * is not reported to pxtcp_pcb_sent().  If we send something
+         * now and immediately close (think "daytime", e.g.)  while
+         * still in SYN_RCVD state, we will move directly to
+         * FIN_WAIT_1 and when our confirming SYN is ACK'ed lwip will
+         * report it to pxtcp_pcb_sent().
+         */
+        DPRINTF2(("forward_inbound: pxtcp %p; pcb %p %s - later...\n",
+                  (void *)pxtcp, (void *)pcb, tcp_debug_state_str(pcb->state)));
+        return;
+    }
+
+
+    beg = pxtcp->inbuf.unsent;  /* private to lwip thread */
+    lim = pxtcp->inbuf.vacant;
+
+    if (beg == lim) {
+        if (pxtcp->inbound_close && !pxtcp->inbound_close_done) {
+            pxtcp_pcb_forward_inbound_close(pxtcp);
+            tcp_output(pcb);
+            return;
+        }
+
+        /*
+         * Else, there's no data to send.
+         *
+         * If there is free space in the buffer, producer will
+         * reschedule us as it receives more data and vacant (lim)
+         * advances.
+         *
+         * If buffer is full when all data have been passed to
+         * tcp_write() but not yet acknowledged, we will advance
+         * unacked on ACK, freeing some space for producer to write to
+         * (then see above).
+         */
+        return;
+    }
+
+    sndbuf = tcp_sndbuf(pcb);
+    if (sndbuf == 0) {
+        /*
+         * Can't send anything now.  As guest ACKs some data, TCP will
+         * call pxtcp_pcb_sent() callback and we will come here again.
+         */
+        return;
+    }
+
+    nsent = 0;
+
+    /*
+     * We have three limits to consider:
+     * - how much data we have in the ringbuf
+     * - how much data we are allowed to send
+     * - ringbuf size
+     */
+    toeob = pxtcp->inbuf.bufsize - beg;
+    if (lim < beg) {            /* lim wrapped */
+        if (sndbuf < toeob) {   /* but we are limited by sndbuf */
+            /* so beg is not going to wrap, treat sndbuf as lim */
+            lim = beg + sndbuf; /* ... and proceed to the simple case */
+        }
+        else { /* we are limited by the end of the buffer, beg will wrap */
+            u8_t maybemore;
+            if (toeob == sndbuf || lim == 0) {
+                maybemore = 0;
+            }
+            else {
+                maybemore = TCP_WRITE_FLAG_MORE;
+            }
+
+            Assert(toeob == (u16_t)toeob);
+            error = tcp_write(pcb, &pxtcp->inbuf.buf[beg], (u16_t)toeob, maybemore);
+            if (error != ERR_OK) {
+                goto writeerr;
+            }
+            nsent += toeob;
+            pxtcp->inbuf.unsent = 0; /* wrap */
+
+            if (maybemore) {
+                beg = 0;
+                sndbuf -= toeob;
+            }
+            else {
+                /* we are done sending, but ... */
+                goto check_inbound_close;
+            }
+        }
+    }
+
+    LWIP_ASSERT1(beg < lim);
+    sndlim = beg + sndbuf;
+    if (lim > sndlim) {
+        lim = sndlim;
+    }
+    tolim = lim - beg;
+    if (tolim > 0) {
+        error = tcp_write(pcb, &pxtcp->inbuf.buf[beg], (u16_t)tolim, 0);
+        if (error != ERR_OK) {
+            goto writeerr;
+        }
+        nsent += tolim;
+        pxtcp->inbuf.unsent = lim;
+    }
+
+  check_inbound_close:
+    if (pxtcp->inbound_close && pxtcp->inbuf.unsent == pxtcp->inbuf.vacant) {
+        pxtcp_pcb_forward_inbound_close(pxtcp);
+    }
+
+    DPRINTF2(("forward_inbound: pxtcp %p, pcb %p: sent %d bytes\n",
+              (void *)pxtcp, (void *)pcb, (int)nsent));
+    tcp_output(pcb);
+    pxtcp_pcb_cancel_poll(pxtcp);
+    return;
+
+  writeerr:
+    if (error == ERR_MEM) {
+        if (nsent > 0) {    /* first write succeeded, second failed */
+            DPRINTF2(("forward_inbound: pxtcp %p, pcb %p: sent %d bytes only\n",
+                      (void *)pxtcp, (void *)pcb, (int)nsent));
+            tcp_output(pcb);
+        }
+        DPRINTF(("forward_inbound: pxtcp %p, pcb %p: ERR_MEM\n",
+                 (void *)pxtcp, (void *)pcb));
+        pxtcp_pcb_schedule_poll(pxtcp);
+    }
+    else {
+        DPRINTF(("forward_inbound: pxtcp %p, pcb %p: %s\n",
+                 (void *)pxtcp, (void *)pcb, proxy_lwip_strerr(error)));
+
+        /* XXX: We shouldn't get ERR_ARG.  Check ERR_CONN conditions early? */
+        LWIP_ASSERT1(error == ERR_MEM);
+    }
+}
+
+
+static void
+pxtcp_pcb_forward_inbound_close(struct pxtcp *pxtcp)
+{
+    struct tcp_pcb *pcb;
+    err_t error;
+
+    LWIP_ASSERT1(pxtcp != NULL);
+    LWIP_ASSERT1(pxtcp->inbound_close);
+    LWIP_ASSERT1(!pxtcp->inbound_close_done);
+    LWIP_ASSERT1(pxtcp->inbuf.unsent == pxtcp->inbuf.vacant);
+
+    pcb = pxtcp->pcb;
+    LWIP_ASSERT1(pcb != NULL);
+
+    DPRINTF(("inbound_close: pxtcp %p; pcb %p: %s\n",
+             (void *)pxtcp, (void *)pcb, tcp_debug_state_str(pcb->state)));
+
+    error = tcp_shutdown(pcb, /*RX*/ 0, /*TX*/ 1);
+    if (error != ERR_OK) {
+        DPRINTF(("inbound_close: pxtcp %p; pcb %p:"
+                 " tcp_shutdown: error=%s\n",
+                 (void *)pxtcp, (void *)pcb, proxy_lwip_strerr(error)));
+        pxtcp_pcb_schedule_poll(pxtcp);
+        return;
+    }
+
+    pxtcp_pcb_cancel_poll(pxtcp);
+    pxtcp->inbound_close_done = 1;
+
+
+    /*
+     * If we have already done outbound close previously (passive
+     * close on the pcb), then we must not hold onto a pcb in LAST_ACK
+     * state since those will be deleted by lwip when that last ack
+     * comes from the guest.
+     *
+     * NB: We do NOT check for deferred delete here, even though we
+     * have just set one of its conditions, inbound_close_done.  We
+     * let pcb callbacks that called us do that.  It's simpler and
+     * cleaner that way.
+     */
+    if (pxtcp->outbound_close_done && pxtcp_pcb_forward_inbound_done(pxtcp)) {
+        pxtcp_pcb_dissociate(pxtcp);
+    }
+}
+
+
+/**
+ * Check that all forwarded inbound data is sent and acked, and that
+ * inbound close is scheduled (we aren't called back when it's acked).
+ */
+DECLINLINE(int)
+pxtcp_pcb_forward_inbound_done(const struct pxtcp *pxtcp)
+{
+    return (pxtcp->inbound_close_done /* also implies that all data forwarded */
+            && pxtcp->inbuf.unacked == pxtcp->inbuf.unsent);
+}
+
+
+/**
+ * tcp_sent() callback - guest acknowledged len bytes.
+ *
+ * We can advance inbuf::unacked index, making more free space in the
+ * ringbuf and wake up producer on poll manager thread.
+ *
+ * We can also try to send more data if we have any since pcb->snd_buf
+ * was increased and we are now permitted to send more.
+ */
+static err_t
+pxtcp_pcb_sent(void *arg, struct tcp_pcb *pcb, u16_t len)
+{
+    struct pxtcp *pxtcp = (struct pxtcp *)arg;
+    size_t unacked;
+
+    LWIP_ASSERT1(pxtcp != NULL);
+    LWIP_ASSERT1(pxtcp->pcb == pcb);
+    LWIP_ASSERT1(pcb->callback_arg == pxtcp);
+    LWIP_UNUSED_ARG(pcb);       /* only in assert */
+
+    DPRINTF2(("%s: pxtcp %p; pcb %p: +%d ACKed:"
+              " unacked %d, unsent %d, vacant %d\n",
+              __func__, (void *)pxtcp, (void *)pcb, (int)len,
+              (int)pxtcp->inbuf.unacked,
+              (int)pxtcp->inbuf.unsent,
+              (int)pxtcp->inbuf.vacant));
+
+    if (/* __predict_false */ len == 0) {
+        /* we are notified to start pulling */
+        LWIP_ASSERT1(!pxtcp->inbound_close);
+        LWIP_ASSERT1(pxtcp->inbound_pull);
+
+        unacked = pxtcp->inbuf.unacked;
+    }
+    else {
+        /*
+         * Advance unacked index.  Guest acknowledged the data, so it
+         * won't be needed again for potential retransmits.
+         */
+        unacked = pxtcp->inbuf.unacked + len;
+        if (unacked > pxtcp->inbuf.bufsize) {
+            unacked -= pxtcp->inbuf.bufsize;
+        }
+        pxtcp->inbuf.unacked = unacked;
+    }
+
+    /* arrange for more inbound data */
+    if (!pxtcp->inbound_close) {
+        if (!pxtcp->inbound_pull) {
+            /* wake up producer, in case it has stopped polling for POLLIN */
+            pxtcp_chan_send_weak(POLLMGR_CHAN_PXTCP_POLLIN, pxtcp);
+#ifdef RT_OS_WINDOWS
+            /**
+             * We have't got enought room in ring buffer to read atm,
+             * but we don't want to lose notification from WSAW4ME when
+             * space would be available, so we reset event with empty recv
+             */
+            recv(pxtcp->sock, NULL, 0, 0);
+#endif
+        }
+        else {
+            ssize_t nread;
+            int stop_pollin;    /* ignored */
+
+            nread = pxtcp_sock_read(pxtcp, &stop_pollin);
+
+            if (nread < 0) {
+                int sockerr = -(int)nread;
+                LWIP_UNUSED_ARG(sockerr);
+                DPRINTF0(("%s: sock %d: %R[sockerr]\n",
+                          __func__, pxtcp->sock, sockerr));
+
+#if HAVE_TCP_POLLHUP == POLLIN /* see counterpart in pxtcp_pmgr_pump() */
+                /*
+                 * It may still be registered with poll manager for POLLOUT.
+                 */
+                pxtcp_chan_send_weak(POLLMGR_CHAN_PXTCP_RESET, pxtcp);
+                return ERR_OK;
+#else
+                /*
+                 * It is no longer registered with poll manager so we
+                 * can kill it directly.
+                 */
+                pxtcp_pcb_reset_pxtcp(pxtcp);
+                return ERR_ABRT;
+#endif
+            }
+        }
+    }
+
+    /* forward more data if we can */
+    if (!pxtcp->inbound_close_done) {
+        pxtcp_pcb_forward_inbound(pxtcp);
+
+        /*
+         * NB: we might have dissociated from a pcb that transitioned
+         * to LAST_ACK state, so don't refer to pcb below.
+         */
+    }
+
+
+    /* have we got all the acks? */
+    if (pxtcp->inbound_close                          /* no more new data */
+        && pxtcp->inbuf.unsent == pxtcp->inbuf.vacant /* all data is sent */
+        && unacked == pxtcp->inbuf.unsent)            /* ... and is acked */
+    {
+        char *buf;
+
+        DPRINTF(("%s: pxtcp %p; pcb %p; all data ACKed\n",
+                 __func__, (void *)pxtcp, (void *)pxtcp->pcb));
+
+        /* no more retransmits, so buf is not needed */
+        buf = pxtcp->inbuf.buf;
+        pxtcp->inbuf.buf = NULL;
+        free(buf);
+
+        /* no more acks, so no more callbacks */
+        if (pxtcp->pcb != NULL) {
+            tcp_sent(pxtcp->pcb, NULL);
+        }
+
+        /*
+         * We may be the last callback for this pcb if we have also
+         * successfully forwarded inbound_close.
+         */
+        pxtcp_pcb_maybe_deferred_delete(pxtcp);
+    }
+
+    return ERR_OK;
+}
+
+
+#if HAVE_TCP_POLLHUP
+/**
+ * Callback from poll manager (pxtcp::msg_inpull) to switch
+ * pxtcp_pcb_sent() to actively pull the last bits of input.  See
+ * POLLHUP comment in pxtcp_pmgr_pump().
+ *
+ * pxtcp::sock is deregistered from poll manager after this callback
+ * is scheduled.
+ */
+static void
+pxtcp_pcb_pull_inbound(void *ctx)
+{
+    struct pxtcp *pxtcp = (struct pxtcp *)ctx;
+    LWIP_ASSERT1(pxtcp != NULL);
+
+    if (pxtcp->pcb == NULL) {
+        DPRINTF(("%s: pxtcp %p: PCB IS GONE\n", __func__, (void *)pxtcp));
+        pxtcp_pcb_reset_pxtcp(pxtcp);
+        return;
+    }
+
+    pxtcp->inbound_pull = 1;
+    if (pxtcp->pmhdl.slot < 0) {
+        DPRINTF(("%s: pxtcp %p: pcb %p (deferred delete)\n",
+                 __func__, (void *)pxtcp, (void *)pxtcp->pcb));
+        pxtcp->deferred_delete = 1;
+    }
+    else {
+        DPRINTF(("%s: pxtcp %p: pcb %p\n",
+                 __func__, (void *)pxtcp, (void *)pxtcp->pcb));
+    }
+
+    pxtcp_pcb_sent(pxtcp, pxtcp->pcb, 0);
+}
+#endif  /* HAVE_TCP_POLLHUP */
+
+
+/**
+ * tcp_err() callback.
+ *
+ * pcb is not passed to this callback since it may be already
+ * deallocated by the stack, but we can't do anything useful with it
+ * anyway since connection is gone.
+ */
+static void
+pxtcp_pcb_err(void *arg, err_t error)
+{
+    struct pxtcp *pxtcp = (struct pxtcp *)arg;
+    LWIP_ASSERT1(pxtcp != NULL);
+
+    /*
+     * ERR_CLSD is special - it is reported here when:
+     *
+     * . guest has already half-closed
+     * . we send FIN to guest when external half-closes
+     * . guest acks that FIN
+     *
+     * Since connection is closed but receive has been already closed
+     * lwip can only report this via tcp_err.  At this point the pcb
+     * is still alive, so we can peek at it if need be.
+     *
+     * The interesting twist is when the ACK from guest that akcs our
+     * FIN also acks some data.  In this scenario lwip will NOT call
+     * tcp_sent() callback with the ACK for that last bit of data but
+     * instead will call tcp_err with ERR_CLSD right away.  Since that
+     * ACK also acknowledges all the data, we should run some of
+     * pxtcp_pcb_sent() logic here.
+     */
+    if (error == ERR_CLSD) {
+        struct tcp_pcb *pcb = pxtcp->pcb; /* still alive */
+
+        DPRINTF2(("ERR_CLSD: pxtcp %p; pcb %p:"
+                  " pcb->acked %d;"
+                  " unacked %d, unsent %d, vacant %d\n",
+                  (void *)pxtcp, (void *)pcb,
+                  pcb->acked,
+                  (int)pxtcp->inbuf.unacked,
+                  (int)pxtcp->inbuf.unsent,
+                  (int)pxtcp->inbuf.vacant));
+
+        LWIP_ASSERT1(pxtcp->pcb == pcb);
+        LWIP_ASSERT1(pcb->callback_arg == pxtcp);
+
+        if (pcb->acked > 0) {
+            pxtcp_pcb_sent(pxtcp, pcb, pcb->acked);
+        }
+        return;
+    }
+
+    DPRINTF0(("tcp_err: pxtcp=%p, error=%s\n",
+              (void *)pxtcp, proxy_lwip_strerr(error)));
+
+    pxtcp->pcb = NULL;          /* pcb is gone */
+    if (pxtcp->deferred_delete) {
+        pxtcp_pcb_reset_pxtcp(pxtcp);
+    }
+    else {
+        pxtcp_chan_send_weak(POLLMGR_CHAN_PXTCP_RESET, pxtcp);
+    }
+}
diff --git a/src/VBox/NetworkServices/NAT/pxtcp.h b/src/VBox/NetworkServices/NAT/pxtcp.h
new file mode 100644
index 00000000..6e182411
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/pxtcp.h
@@ -0,0 +1,52 @@
+/* $Id: pxtcp.h $ */
+/** @file
+ * NAT Network - TCP proxy, internal interface declarations.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#ifndef VBOX_INCLUDED_SRC_NAT_pxtcp_h
+#define VBOX_INCLUDED_SRC_NAT_pxtcp_h
+#ifndef RT_WITHOUT_PRAGMA_ONCE
+# pragma once
+#endif
+
+#include "lwip/err.h"
+#include "lwip/ip_addr.h"
+
+struct pbuf;
+struct tcp_pcb;
+struct pxtcp;
+struct fwspec;
+
+err_t pxtcp_pcb_accept_outbound(struct tcp_pcb *, struct pbuf *, int, ipX_addr_t *, u16_t);
+
+struct pxtcp *pxtcp_create_forwarded(SOCKET);
+void pxtcp_cancel_forwarded(struct pxtcp *);
+
+void pxtcp_pcb_connect(struct pxtcp *, const struct fwspec *);
+
+int pxtcp_pmgr_add(struct pxtcp *);
+void pxtcp_pmgr_del(struct pxtcp *);
+
+#endif /* !VBOX_INCLUDED_SRC_NAT_pxtcp_h */
diff --git a/src/VBox/NetworkServices/NAT/pxudp.c b/src/VBox/NetworkServices/NAT/pxudp.c
new file mode 100644
index 00000000..1c8fab12
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/pxudp.c
@@ -0,0 +1,858 @@
+/* $Id: pxudp.c $ */
+/** @file
+ * NAT Network - UDP proxy.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#define LOG_GROUP LOG_GROUP_NAT_SERVICE
+
+#include "winutils.h"
+#include "proxy.h"
+#include "proxy_pollmgr.h"
+#include "pxremap.h"
+
+#ifndef RT_OS_WINDOWS
+#include <sys/types.h>
+#include <sys/socket.h>
+#ifdef RT_OS_DARWIN
+# define __APPLE_USE_RFC_3542
+#endif
+#include <netinet/in.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <poll.h>
+
+#include <err.h>                /* BSD'ism */
+#else
+#include <stdlib.h>
+#include <iprt/stdint.h>
+#include <stdio.h>
+#include "winpoll.h"
+#endif
+
+#include "lwip/opt.h"
+
+#include "lwip/sys.h"
+#include "lwip/tcpip.h"
+#include "lwip/udp.h"
+#include "lwip/icmp.h"
+
+struct pxudp {
+    /**
+     * Our poll manager handler.
+     */
+    struct pollmgr_handler pmhdl;
+
+    /**
+     * lwIP ("internal") side of the proxied connection.
+     */
+    struct udp_pcb *pcb;
+
+    /**
+     * Host ("external") side of the proxied connection.
+     */
+    SOCKET sock;
+
+    /**
+     * Is this pcb a mapped host loopback?
+     */
+    int is_mapped;
+
+    /**
+     * Cached value of TTL socket option.
+     */
+    int ttl;
+
+    /**
+     * Cached value of TOS socket option.
+     */
+    int tos;
+
+    /**
+     * Cached value of "don't fragment" socket option.
+     */
+    int df;
+
+    /**
+     * For some protocols (notably: DNS) we know we are getting just
+     * one reply, so we don't want the pcb and the socket to sit there
+     * waiting to be g/c'ed by timeout.  This field counts request and
+     * replies for them.
+     */
+    int count;
+
+    /**
+     * Mailbox for inbound pbufs.
+     *
+     * XXX: since we have single producer and single consumer we can
+     * use lockless ringbuf like for pxtcp.
+     */
+    sys_mbox_t inmbox;
+
+    /**
+     * lwIP thread's strong reference to us.
+     */
+    struct pollmgr_refptr *rp;
+
+    /*
+     * We use static messages to void malloc/free overhead.
+     */
+    struct tcpip_msg msg_delete;   /* delete pxudp */
+    struct tcpip_msg msg_inbound;  /* trigger send of inbound data */
+};
+
+
+static struct pxudp *pxudp_allocate(void);
+static void pxudp_drain_inmbox(struct pxudp *);
+static void pxudp_free(struct pxudp *);
+
+static struct udp_pcb *pxudp_pcb_dissociate(struct pxudp *);
+
+/* poll manager callbacks for pxudp related channels */
+static int pxudp_pmgr_chan_add(struct pollmgr_handler *, SOCKET, int);
+static int pxudp_pmgr_chan_del(struct pollmgr_handler *, SOCKET, int);
+
+/* helper functions for sending/receiving pxudp over poll manager channels */
+static ssize_t pxudp_chan_send(enum pollmgr_slot_t, struct pxudp *);
+static ssize_t pxudp_chan_send_weak(enum pollmgr_slot_t, struct pxudp *);
+static struct pxudp *pxudp_chan_recv(struct pollmgr_handler *, SOCKET, int);
+static struct pxudp *pxudp_chan_recv_strong(struct pollmgr_handler *, SOCKET, int);
+
+/* poll manager callbacks for individual sockets */
+static int pxudp_pmgr_pump(struct pollmgr_handler *, SOCKET, int);
+
+/* convenience function for poll manager callback */
+static int pxudp_schedule_delete(struct pxudp *);
+
+/* lwip thread callbacks called via proxy_lwip_post() */
+static void pxudp_pcb_delete_pxudp(void *);
+
+/* outbound ttl check */
+static int pxudp_ttl_expired(struct pbuf *);
+
+/* udp pcb callbacks &c */
+static void pxudp_pcb_accept(void *, struct udp_pcb *, struct pbuf *, ip_addr_t *, u16_t);
+static void pxudp_pcb_recv(void *, struct udp_pcb *, struct pbuf *, ip_addr_t *, u16_t);
+static void pxudp_pcb_forward_outbound(struct pxudp *, struct pbuf *, ip_addr_t *, u16_t);
+static void pxudp_pcb_expired(struct pxudp *);
+static void pxudp_pcb_write_inbound(void *);
+static void pxudp_pcb_forward_inbound(struct pxudp *);
+
+/* poll manager handlers for pxudp channels */
+static struct pollmgr_handler pxudp_pmgr_chan_add_hdl;
+static struct pollmgr_handler pxudp_pmgr_chan_del_hdl;
+
+
+void
+pxudp_init(void)
+{
+    /*
+     * Create channels.
+     */
+    pxudp_pmgr_chan_add_hdl.callback = pxudp_pmgr_chan_add;
+    pxudp_pmgr_chan_add_hdl.data = NULL;
+    pxudp_pmgr_chan_add_hdl.slot = -1;
+    pollmgr_add_chan(POLLMGR_CHAN_PXUDP_ADD, &pxudp_pmgr_chan_add_hdl);
+
+    pxudp_pmgr_chan_del_hdl.callback = pxudp_pmgr_chan_del;
+    pxudp_pmgr_chan_del_hdl.data = NULL;
+    pxudp_pmgr_chan_del_hdl.slot = -1;
+    pollmgr_add_chan(POLLMGR_CHAN_PXUDP_DEL, &pxudp_pmgr_chan_del_hdl);
+
+    udp_proxy_accept(pxudp_pcb_accept);
+}
+
+
+/**
+ * Syntactic sugar for sending pxudp pointer over poll manager
+ * channel.  Used by lwip thread functions.
+ */
+static ssize_t
+pxudp_chan_send(enum pollmgr_slot_t chan, struct pxudp *pxudp)
+{
+    return pollmgr_chan_send(chan, &pxudp, sizeof(pxudp));
+}
+
+
+/**
+ * Syntactic sugar for sending weak reference to pxudp over poll
+ * manager channel.  Used by lwip thread functions.
+ */
+static ssize_t
+pxudp_chan_send_weak(enum pollmgr_slot_t chan, struct pxudp *pxudp)
+{
+    pollmgr_refptr_weak_ref(pxudp->rp);
+    return pollmgr_chan_send(chan, &pxudp->rp, sizeof(pxudp->rp));
+}
+
+
+/**
+ * Counterpart of pxudp_chan_send().
+ */
+static struct pxudp *
+pxudp_chan_recv(struct pollmgr_handler *handler, SOCKET fd, int revents)
+{
+    struct pxudp *pxudp;
+
+    pxudp = (struct pxudp *)pollmgr_chan_recv_ptr(handler, fd, revents);
+    return pxudp;
+}
+
+
+/**
+ * Counterpart of pxudp_chan_send_weak().
+ */
+struct pxudp *
+pxudp_chan_recv_strong(struct pollmgr_handler *handler, SOCKET fd, int revents)
+{
+    struct pollmgr_refptr *rp;
+    struct pollmgr_handler *base;
+    struct pxudp *pxudp;
+
+    rp = (struct pollmgr_refptr *)pollmgr_chan_recv_ptr(handler, fd, revents);
+    base = (struct pollmgr_handler *)pollmgr_refptr_get(rp);
+    pxudp = (struct pxudp *)base;
+
+    return pxudp;
+}
+
+
+/**
+ * POLLMGR_CHAN_PXUDP_ADD handler.
+ *
+ * Get new pxudp from lwip thread and start polling its socket.
+ */
+static int
+pxudp_pmgr_chan_add(struct pollmgr_handler *handler, SOCKET fd, int revents)
+{
+    struct pxudp *pxudp;
+    int status;
+
+    pxudp = pxudp_chan_recv(handler, fd, revents);
+    DPRINTF(("pxudp_add: new pxudp %p; pcb %p\n",
+             (void *)pxudp, (void *)pxudp->pcb));
+
+    LWIP_ASSERT1(pxudp != NULL);
+    LWIP_ASSERT1(pxudp->pmhdl.callback != NULL);
+    LWIP_ASSERT1(pxudp->pmhdl.data = (void *)pxudp);
+    LWIP_ASSERT1(pxudp->pmhdl.slot < 0);
+
+
+    status = pollmgr_add(&pxudp->pmhdl, pxudp->sock, POLLIN);
+    if (status < 0) {
+        pxudp_schedule_delete(pxudp);
+    }
+
+    return POLLIN;
+}
+
+
+/**
+ * POLLMGR_CHAN_PXUDP_DEL handler.
+ */
+static int
+pxudp_pmgr_chan_del(struct pollmgr_handler *handler, SOCKET fd, int revents)
+{
+    struct pxudp *pxudp;
+
+    pxudp = pxudp_chan_recv_strong(handler, fd, revents);
+    if (pxudp == NULL) {
+        return POLLIN;
+    }
+
+    DPRINTF(("pxudp_del: pxudp %p; socket %d\n", (void *)pxudp, pxudp->sock));
+
+    pollmgr_del_slot(pxudp->pmhdl.slot);
+
+    /*
+     * Go back to lwip thread to delete after any pending callbacks
+     * for unprocessed inbound traffic are drained.
+     */
+    pxudp_schedule_delete(pxudp);
+
+    return POLLIN;
+}
+
+
+static struct pxudp *
+pxudp_allocate(void)
+{
+    struct pxudp *pxudp;
+    err_t error;
+
+    pxudp = (struct pxudp *)malloc(sizeof(*pxudp));
+    if (pxudp == NULL) {
+        return NULL;
+    }
+
+    pxudp->pmhdl.callback = NULL;
+    pxudp->pmhdl.data = (void *)pxudp;
+    pxudp->pmhdl.slot = -1;
+
+    pxudp->pcb = NULL;
+    pxudp->sock = INVALID_SOCKET;
+    pxudp->df = -1;
+    pxudp->ttl = -1;
+    pxudp->tos = -1;
+    pxudp->count = 0;
+
+    pxudp->rp = pollmgr_refptr_create(&pxudp->pmhdl);
+    if (pxudp->rp == NULL) {
+        free(pxudp);
+        return NULL;
+    }
+
+    error = sys_mbox_new(&pxudp->inmbox, 16);
+    if (error != ERR_OK) {
+        pollmgr_refptr_unref(pxudp->rp);
+        free(pxudp);
+        return NULL;
+    }
+
+#define CALLBACK_MSG(MSG, FUNC)                         \
+    do {                                                \
+        pxudp->MSG.type = TCPIP_MSG_CALLBACK_STATIC;    \
+        pxudp->MSG.sem = NULL;                          \
+        pxudp->MSG.msg.cb.function = FUNC;              \
+        pxudp->MSG.msg.cb.ctx = (void *)pxudp;          \
+    } while (0)
+
+    CALLBACK_MSG(msg_delete, pxudp_pcb_delete_pxudp);
+    CALLBACK_MSG(msg_inbound, pxudp_pcb_write_inbound);
+
+    return pxudp;
+}
+
+
+static void
+pxudp_drain_inmbox(struct pxudp *pxudp)
+{
+    void *ptr;
+
+    if (!sys_mbox_valid(&pxudp->inmbox)) {
+        return;
+    }
+
+    while (sys_mbox_tryfetch(&pxudp->inmbox, &ptr) != SYS_MBOX_EMPTY) {
+        struct pbuf *p = (struct pbuf *)ptr;
+        pbuf_free(p);
+    }
+
+    sys_mbox_free(&pxudp->inmbox);
+    sys_mbox_set_invalid(&pxudp->inmbox);
+}
+
+
+static void
+pxudp_free(struct pxudp *pxudp)
+{
+    pxudp_drain_inmbox(pxudp);
+    free(pxudp);
+}
+
+
+/**
+ * Dissociate pxudp and its udp_pcb.
+ *
+ * Unlike its TCP cousin returns the pcb since UDP pcbs need to be
+ * actively deleted, so save callers the trouble of saving a copy
+ * before calling us.
+ */
+static struct udp_pcb *
+pxudp_pcb_dissociate(struct pxudp *pxudp)
+{
+    struct udp_pcb *pcb;
+
+    if (pxudp == NULL || pxudp->pcb == NULL) {
+        return NULL;
+    }
+
+    pcb = pxudp->pcb;
+
+    udp_recv(pxudp->pcb, NULL, NULL);
+    pxudp->pcb = NULL;
+
+    return pcb;
+}
+
+
+/**
+ * Lwip thread callback invoked via pxudp::msg_delete
+ *
+ * Since we use static messages to communicate to the lwip thread, we
+ * cannot delete pxudp without making sure there are no unprocessed
+ * messages in the lwip thread mailbox.
+ *
+ * The easiest way to ensure that is to send this "delete" message as
+ * the last one and when it's processed we know there are no more and
+ * it's safe to delete pxudp.
+ *
+ * Channel callback should use pxudp_schedule_delete() convenience
+ * function defined below.
+ */
+static void
+pxudp_pcb_delete_pxudp(void *arg)
+{
+    struct pxudp *pxudp = (struct pxudp *)arg;
+    struct udp_pcb *pcb;
+
+    LWIP_ASSERT1(pxudp != NULL);
+
+    if (pxudp->sock != INVALID_SOCKET) {
+        closesocket(pxudp->sock);
+        pxudp->sock = INVALID_SOCKET;
+    }
+
+    pcb = pxudp_pcb_dissociate(pxudp);
+    if (pcb != NULL) {
+        udp_remove(pcb);
+    }
+
+    pollmgr_refptr_unref(pxudp->rp);
+    pxudp_free(pxudp);
+}
+
+
+/**
+ * Poll manager callback should use this convenience wrapper to
+ * schedule pxudp deletion on the lwip thread and to deregister from
+ * the poll manager.
+ */
+static int
+pxudp_schedule_delete(struct pxudp *pxudp)
+{
+    /*
+     * If pollmgr_refptr_get() is called by any channel before
+     * scheduled deletion happens, let them know we are gone.
+     */
+    pxudp->pmhdl.slot = -1;
+
+    /*
+     * Schedule deletion.  Since poll manager thread may be pre-empted
+     * right after we send the message, the deletion may actually
+     * happen on the lwip thread before we return from this function,
+     * so it's not safe to refer to pxudp after this call.
+     */
+    proxy_lwip_post(&pxudp->msg_delete);
+
+    /* tell poll manager to deregister us */
+    return -1;
+}
+
+
+/**
+ * Outbound TTL/HOPL check.
+ */
+static int
+pxudp_ttl_expired(struct pbuf *p)
+{
+    int ttl;
+
+    if (ip_current_is_v6()) {
+        ttl = IP6H_HOPLIM(ip6_current_header());
+    }
+    else {
+        ttl = IPH_TTL(ip_current_header());
+    }
+
+    if (RT_UNLIKELY(ttl <= 1)) {
+        int status = pbuf_header(p, ip_current_header_tot_len() + UDP_HLEN);
+        if (RT_LIKELY(status == 0)) {
+            if (ip_current_is_v6()) {
+                icmp6_time_exceeded(p, ICMP6_TE_HL);
+            }
+            else {
+                icmp_time_exceeded(p, ICMP_TE_TTL);
+            }
+        }
+        pbuf_free(p);
+        return 1;
+    }
+
+    return 0;
+}
+
+
+/**
+ * New proxied UDP conversation created.
+ * Global callback for udp_proxy_accept().
+ */
+static void
+pxudp_pcb_accept(void *arg, struct udp_pcb *newpcb, struct pbuf *p,
+                 ip_addr_t *addr, u16_t port)
+{
+    struct pxudp *pxudp;
+    ipX_addr_t dst_addr;
+    int mapping;
+    int sdom;
+    SOCKET sock;
+
+    LWIP_ASSERT1(newpcb != NULL);
+    LWIP_ASSERT1(p != NULL);
+    LWIP_UNUSED_ARG(arg);
+
+    mapping = pxremap_outbound_ipX(PCB_ISIPV6(newpcb), &dst_addr, &newpcb->local_ip);
+    if (mapping != PXREMAP_MAPPED && pxudp_ttl_expired(p)) {
+        udp_remove(newpcb);
+        return;
+    }
+
+    pxudp = pxudp_allocate();
+    if (pxudp == NULL) {
+        DPRINTF(("pxudp_allocate: failed\n"));
+        udp_remove(newpcb);
+        pbuf_free(p);
+        return;
+    }
+
+    sdom = PCB_ISIPV6(newpcb) ? PF_INET6 : PF_INET;
+    pxudp->is_mapped = (mapping == PXREMAP_MAPPED);
+
+#if 0 /* XXX: DNS IPv6->IPv4 remapping hack */
+    if (pxudp->is_mapped
+        && newpcb->local_port == 53
+        && PCB_ISIPV6(newpcb))
+    {
+        /*
+         * "Remap" DNS over IPv6 to IPv4 since Ubuntu dnsmasq does not
+         * listen on IPv6.
+         */
+        sdom = PF_INET;
+        ipX_addr_set_loopback(0, &dst_addr);
+    }
+#endif  /* DNS IPv6->IPv4 remapping hack */
+
+    sock = proxy_connected_socket(sdom, SOCK_DGRAM,
+                                  &dst_addr, newpcb->local_port);
+    if (sock == INVALID_SOCKET) {
+        udp_remove(newpcb);
+        pbuf_free(p);
+        return;
+    }
+
+    pxudp->sock = sock;
+    pxudp->pcb = newpcb;
+    udp_recv(newpcb, pxudp_pcb_recv, pxudp);
+
+    pxudp->pmhdl.callback = pxudp_pmgr_pump;
+    pxudp_chan_send(POLLMGR_CHAN_PXUDP_ADD, pxudp);
+
+    /* dispatch directly instead of calling pxudp_pcb_recv() */
+    pxudp_pcb_forward_outbound(pxudp, p, addr, port);
+}
+
+
+/**
+ * udp_recv() callback.
+ */
+static void
+pxudp_pcb_recv(void *arg, struct udp_pcb *pcb, struct pbuf *p,
+               ip_addr_t *addr, u16_t port)
+{
+    struct pxudp *pxudp = (struct pxudp *)arg;
+
+    LWIP_ASSERT1(pxudp != NULL);
+    LWIP_ASSERT1(pcb == pxudp->pcb);
+    LWIP_UNUSED_ARG(pcb);
+
+    if (p != NULL) {
+        pxudp_pcb_forward_outbound(pxudp, p, addr, port);
+    }
+    else {
+        pxudp_pcb_expired(pxudp);
+    }
+}
+
+
+static void
+pxudp_pcb_forward_outbound(struct pxudp *pxudp, struct pbuf *p,
+                           ip_addr_t *addr, u16_t port)
+{
+    int status;
+
+    LWIP_UNUSED_ARG(addr);
+    LWIP_UNUSED_ARG(port);
+
+    if (!pxudp->is_mapped && pxudp_ttl_expired(p)) {
+        return;
+    }
+
+    if (!ip_current_is_v6()) { /* IPv4 */
+        const struct ip_hdr *iph = ip_current_header();
+        int ttl, tos, df;
+
+        /*
+         * Different OSes have different socket options for DF.
+         * Unlike pxping.c, we can't use IP_HDRINCL here as it's only
+         * valid for SOCK_RAW.
+         */
+#     define USE_DF_OPTION(_Optname) \
+            const int dfopt = _Optname; \
+            const char * const dfoptname = #_Optname; \
+            RT_NOREF_PV(dfoptname)
+#if   defined(IP_MTU_DISCOVER)  /* Linux */
+        USE_DF_OPTION(IP_MTU_DISCOVER);
+#elif defined(IP_DONTFRAG)      /* Solaris 11+, FreeBSD */
+        USE_DF_OPTION(IP_DONTFRAG);
+#elif defined(IP_DONTFRAGMENT)  /* Windows */
+        USE_DF_OPTION(IP_DONTFRAGMENT);
+#else
+        USE_DF_OPTION(0);
+#endif
+
+        ttl = IPH_TTL(iph);
+        if (!pxudp->is_mapped) {
+            LWIP_ASSERT1(ttl > 1);
+            --ttl;
+        }
+
+        if (ttl != pxudp->ttl) {
+            status = setsockopt(pxudp->sock, IPPROTO_IP, IP_TTL,
+                                (char *)&ttl, sizeof(ttl));
+            if (RT_LIKELY(status == 0)) {
+                pxudp->ttl = ttl;
+            }
+            else {
+                DPRINTF(("IP_TTL: %R[sockerr]\n", SOCKERRNO()));
+            }
+        }
+
+        tos = IPH_TOS(iph);
+        if (tos != pxudp->tos) {
+            status = setsockopt(pxudp->sock, IPPROTO_IP, IP_TOS,
+                                (char *)&tos, sizeof(tos));
+            if (RT_LIKELY(status == 0)) {
+                pxudp->tos = tos;
+            }
+            else {
+                DPRINTF(("IP_TOS: %R[sockerr]\n", SOCKERRNO()));
+            }
+        }
+
+        if (dfopt) {
+            df = (IPH_OFFSET(iph) & PP_HTONS(IP_DF)) != 0;
+#if defined(IP_MTU_DISCOVER)
+            df = df ? IP_PMTUDISC_DO : IP_PMTUDISC_DONT;
+#endif
+            if (df != pxudp->df) {
+                status = setsockopt(pxudp->sock, IPPROTO_IP, dfopt,
+                                    (char *)&df, sizeof(df));
+                if (RT_LIKELY(status == 0)) {
+                    pxudp->df = df;
+                }
+                else {
+                    DPRINTF(("%s: %R[sockerr]\n", dfoptname, SOCKERRNO()));
+                }
+            }
+        }
+    }
+    else { /* IPv6 */
+        const struct ip6_hdr *iph = ip6_current_header();
+        int ttl;
+
+        ttl = IP6H_HOPLIM(iph);
+        if (!pxudp->is_mapped) {
+            LWIP_ASSERT1(ttl > 1);
+            --ttl;
+        }
+
+        if (ttl != pxudp->ttl) {
+            status = setsockopt(pxudp->sock, IPPROTO_IPV6, IPV6_UNICAST_HOPS,
+                                (char *)&ttl, sizeof(ttl));
+            if (RT_LIKELY(status == 0)) {
+                pxudp->ttl = ttl;
+            }
+            else {
+                DPRINTF(("IPV6_UNICAST_HOPS: %R[sockerr]\n", SOCKERRNO()));
+            }
+        }
+    }
+
+    if (pxudp->pcb->local_port == 53) {
+        ++pxudp->count;
+    }
+
+    proxy_sendto(pxudp->sock, p, NULL, 0);
+    pbuf_free(p);
+}
+
+
+/**
+ * Proxy udp_pcbs are expired by timer, which is signaled by passing
+ * NULL pbuf to the udp_recv() callback.  At that point the pcb is
+ * removed from the list of proxy udp pcbs so no new datagrams will be
+ * delivered.
+ */
+static void
+pxudp_pcb_expired(struct pxudp *pxudp)
+{
+    struct udp_pcb *pcb;
+
+    DPRINTF2(("%s: pxudp %p, pcb %p, sock %d: expired\n",
+              __func__, (void *)pxudp, (void *)pxudp->pcb, pxudp->sock));
+
+    pcb = pxudp_pcb_dissociate(pxudp);
+    if (pcb != NULL) {
+        udp_remove(pcb);
+    }
+
+    pxudp_chan_send_weak(POLLMGR_CHAN_PXUDP_DEL, pxudp);
+}
+
+
+/**
+ */
+static int
+pxudp_pmgr_pump(struct pollmgr_handler *handler, SOCKET fd, int revents)
+{
+    struct pxudp *pxudp;
+    struct pbuf *p;
+    ssize_t nread;
+    err_t error;
+
+    pxudp = (struct pxudp *)handler->data;
+    LWIP_ASSERT1(handler == &pxudp->pmhdl);
+    LWIP_ASSERT1(fd == pxudp->sock);
+    LWIP_UNUSED_ARG(fd);
+
+
+    if (revents & ~(POLLIN|POLLERR)) {
+        DPRINTF(("%s: unexpected revents 0x%x\n", __func__, revents));
+        return pxudp_schedule_delete(pxudp);
+    }
+
+    /*
+     * XXX: AFAICS, there's no way to match the error with the
+     * outgoing datagram that triggered it, since we do non-blocking
+     * sends from lwip thread.
+     */
+    if (revents & POLLERR) {
+        int sockerr = -1;
+        socklen_t optlen = (socklen_t)sizeof(sockerr);
+        int status;
+
+        status = getsockopt(pxudp->sock, SOL_SOCKET,
+                            SO_ERROR, (char *)&sockerr, &optlen);
+        if (status < 0) {
+            DPRINTF(("%s: sock %d: SO_ERROR failed:%R[sockerr]\n",
+                     __func__, pxudp->sock, SOCKERRNO()));
+        }
+        else {
+            DPRINTF(("%s: sock %d: %R[sockerr]\n",
+                     __func__, pxudp->sock, sockerr));
+        }
+    }
+
+    if ((revents & POLLIN) == 0) {
+        return POLLIN;
+    }
+
+#ifdef RT_OS_WINDOWS
+    nread = recv(pxudp->sock, (char *)pollmgr_udpbuf, sizeof(pollmgr_udpbuf), 0);
+#else
+    nread = recv(pxudp->sock, pollmgr_udpbuf, sizeof(pollmgr_udpbuf), 0);
+#endif
+    if (nread == SOCKET_ERROR) {
+        DPRINTF(("%s: %R[sockerr]\n", __func__, SOCKERRNO()));
+        return POLLIN;
+    }
+
+    p = pbuf_alloc(PBUF_RAW, (u16_t)nread, PBUF_RAM);
+    if (p == NULL) {
+        DPRINTF(("%s: pbuf_alloc(%d) failed\n", __func__, (int)nread));
+        return POLLIN;
+    }
+
+    error = pbuf_take(p, pollmgr_udpbuf, (u16_t)nread);
+    if (error != ERR_OK) {
+        DPRINTF(("%s: pbuf_take(%d) failed\n", __func__, (int)nread));
+        pbuf_free(p);
+        return POLLIN;
+    }
+
+    error = sys_mbox_trypost(&pxudp->inmbox, p);
+    if (error != ERR_OK) {
+        pbuf_free(p);
+        return POLLIN;
+    }
+
+    proxy_lwip_post(&pxudp->msg_inbound);
+
+    return POLLIN;
+}
+
+
+/**
+ * Callback from poll manager to trigger sending to guest.
+ */
+static void
+pxudp_pcb_write_inbound(void *ctx)
+{
+    struct pxudp *pxudp = (struct pxudp *)ctx;
+    LWIP_ASSERT1(pxudp != NULL);
+
+    if (pxudp->pcb == NULL) {
+        return;
+    }
+
+    pxudp_pcb_forward_inbound(pxudp);
+}
+
+
+static void
+pxudp_pcb_forward_inbound(struct pxudp *pxudp)
+{
+    struct pbuf *p;
+    u32_t timo;
+    err_t error;
+
+    if (!sys_mbox_valid(&pxudp->inmbox)) {
+        return;
+    }
+
+    timo = sys_mbox_tryfetch(&pxudp->inmbox, (void **)&p);
+    if (timo == SYS_MBOX_EMPTY) {
+        return;
+    }
+
+    error = udp_send(pxudp->pcb, p);
+    if (error != ERR_OK) {
+        DPRINTF(("%s: udp_send(pcb %p) err %d\n",
+                 __func__, (void *)pxudp, error));
+    }
+
+    pbuf_free(p);
+
+    /*
+     * If we enabled counting in pxudp_pcb_forward_outbound() check
+     * that we have (all) the reply(s).
+     */
+    if (pxudp->count > 0) {
+        --pxudp->count;
+        if (pxudp->count == 0) {
+            pxudp_pcb_expired(pxudp);
+        }
+    }
+}
diff --git a/src/VBox/NetworkServices/NAT/rtmon_bsd.c b/src/VBox/NetworkServices/NAT/rtmon_bsd.c
new file mode 100644
index 00000000..05bec3da
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/rtmon_bsd.c
@@ -0,0 +1,126 @@
+/* $Id: rtmon_bsd.c $ */
+/** @file
+ * NAT Network - IPv6 default route monitor for BSD routing sockets.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+
+#define LOG_GROUP LOG_GROUP_NAT_SERVICE
+
+#include "proxy.h"
+
+#include <sys/types.h>
+#include <sys/socket.h>
+
+#include <net/if_dl.h>
+#include <net/route.h>
+
+#include <netinet/in.h>
+#include <netinet/ip6.h>
+
+#include <errno.h>
+#include <string.h>
+#include <unistd.h>
+
+
+/**
+ * Query IPv6 routing table - BSD routing sockets version.
+ *
+ * We don't actually monitor the routing socket for updates, and
+ * instead query the kernel each time.
+ *
+ * We take a shortcut and don't read the reply to our RTM_GET - if
+ * there's no default IPv6 route, write(2) will fail with ESRCH
+ * synchronously.  In theory it may fail asynchronously and we should
+ * wait for the RTM_GET reply and check rt_msghdr::rtm_errno.
+ *
+ * KAME code in *BSD maintains internally a list of default routers
+ * that it learned from RAs, and installs only one of them into the
+ * routing table (actually, I'm not sure if BSD routing table can
+ * handle multiple routes to the same destination).  One side-effect
+ * of this is that when manually configured route (e.g. teredo) is
+ * deleted, the system will lose its default route even when KAME IPv6
+ * has default router(s) in its internal list.  Next RA will force the
+ * update, though.
+ *
+ * Solaris does expose multiple routes in the routing table and
+ * replies to RTM_GET with "default default".
+ */
+int
+rtmon_get_defaults(void)
+{
+    int rtsock;
+    struct req {
+        struct rt_msghdr rtm;
+        struct sockaddr_in6 dst;
+        struct sockaddr_in6 mask;
+        struct sockaddr_dl ifp;
+    } req;
+    ssize_t nsent;
+
+    rtsock = socket(PF_ROUTE, SOCK_RAW, AF_INET6);
+    if (rtsock < 0) {
+        DPRINTF0(("rtmon: failed to create routing socket\n"));
+        return -1;
+    }
+
+    memset(&req, 0, sizeof(req));
+
+    req.rtm.rtm_type = RTM_GET;
+    req.rtm.rtm_version = RTM_VERSION;
+    req.rtm.rtm_msglen = sizeof(req);
+    req.rtm.rtm_seq = 0x12345;
+
+    req.rtm.rtm_flags = RTF_UP;
+    req.rtm.rtm_addrs = RTA_DST | RTA_NETMASK | RTA_IFP;
+
+    req.dst.sin6_family = AF_INET6;
+#if HAVE_SA_LEN
+    req.dst.sin6_len = sizeof(req.dst);
+#endif
+
+    req.mask.sin6_family = AF_INET6;
+#if HAVE_SA_LEN
+    req.mask.sin6_len = sizeof(req.mask);
+#endif
+
+    req.ifp.sdl_family = AF_LINK;
+#if HAVE_SA_LEN
+    req.ifp.sdl_len = sizeof(req.ifp);
+#endif
+
+    nsent = write(rtsock, &req, req.rtm.rtm_msglen);
+    if (nsent < 0) {
+        if (errno == ESRCH) {
+            /* there's no default route */
+            return 0;
+        }
+        else {
+            DPRINTF0(("rtmon: failed to send RTM_GET\n"));
+            return -1;
+        }
+    }
+
+    return 1;
+}
diff --git a/src/VBox/NetworkServices/NAT/rtmon_linux.c b/src/VBox/NetworkServices/NAT/rtmon_linux.c
new file mode 100644
index 00000000..1ef37e34
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/rtmon_linux.c
@@ -0,0 +1,259 @@
+/* $Id: rtmon_linux.c $ */
+/** @file
+ * NAT Network - IPv6 default route monitor for Linux netlink.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+
+#define LOG_GROUP LOG_GROUP_NAT_SERVICE
+
+#include "proxy.h"
+
+#include <sys/types.h>          /* must come before linux/netlink */
+#include <sys/socket.h>
+
+#include <asm/types.h>
+#include <linux/netlink.h>
+#include <linux/rtnetlink.h>
+
+#include <errno.h>
+#include <string.h>
+#include <unistd.h>
+
+
+static int rtmon_check_defaults(const void *buf, size_t len);
+
+
+/**
+ * Read IPv6 routing table - Linux rtnetlink version.
+ *
+ * XXX: TODO: To avoid re-reading the table we should subscribe to
+ * updates by binding a monitoring NETLINK_ROUTE socket to
+ * sockaddr_nl::nl_groups = RTMGRP_IPV6_ROUTE.
+ *
+ * But that will provide updates only.  Documentation is scarce, but
+ * from what I've seen it seems that to get accurate routing info the
+ * monitoring socket needs to be created first, then full routing
+ * table requested (easier to do via spearate socket), then monitoring
+ * socket polled for input.  The first update(s) of the monitoring
+ * socket may happen before full table is returned, so we can't just
+ * count the defaults, we need to keep track of their { oif, gw } to
+ * correctly ignore updates that are reported via monitoring socket,
+ * but that are already reflected in the full routing table returned
+ * in response to our request.
+ */
+int
+rtmon_get_defaults(void)
+{
+    int rtsock;
+    ssize_t nsent, ssize;
+    int ndefrts;
+
+    char *buf = NULL;
+    size_t bufsize;
+
+    struct {
+        struct nlmsghdr nh;
+        struct rtmsg rtm;
+        char attrbuf[512];
+    } rtreq;
+
+    memset(&rtreq, 0, sizeof(rtreq));
+    rtreq.nh.nlmsg_type = RTM_GETROUTE;
+    rtreq.nh.nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP;
+    rtreq.rtm.rtm_family = AF_INET6;
+    rtreq.rtm.rtm_table = RT_TABLE_MAIN;
+    rtreq.rtm.rtm_protocol = RTPROT_UNSPEC;
+
+    rtreq.nh.nlmsg_len = NLMSG_SPACE(sizeof(rtreq.rtm));
+
+    bufsize = 1024;
+    ssize = bufsize;
+    for (;;) {
+        char *newbuf;
+        int recverr;
+
+        newbuf = (char *)realloc(buf, ssize);
+        if (newbuf == NULL) {
+            DPRINTF0(("rtmon: failed to %sallocate buffer\n",
+                      buf == NULL ? "" : "re"));
+            free(buf);
+            return -1;
+        }
+
+        buf = newbuf;
+        bufsize = ssize;
+
+        /* it's easier to reopen than to flush */
+        rtsock = socket(PF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
+        if (rtsock < 0) {
+            DPRINTF0(("rtmon: failed to create netlink socket: %s", strerror(errno)));
+            free(buf);
+            return -1;
+        }
+
+        nsent = send(rtsock, &rtreq, rtreq.nh.nlmsg_len, 0);
+        if (nsent < 0) {
+            DPRINTF0(("rtmon: RTM_GETROUTE failed: %s", strerror(errno)));
+            close (rtsock);
+            free(buf);
+            return -1;
+        }
+
+        ssize = recv(rtsock, buf, bufsize, MSG_TRUNC);
+        recverr = errno;
+        close (rtsock);
+
+        if (ssize < 0) {
+            DPRINTF(("rtmon: failed to read RTM_GETROUTE response: %s",
+                     strerror(recverr)));
+            free(buf);
+            return -1;
+        }
+
+        if ((size_t)ssize <= bufsize) {
+            DPRINTF2(("rtmon: RTM_GETROUTE: %lu bytes\n",
+                      (unsigned long)ssize));
+            break;
+        }
+
+        DPRINTF2(("rtmon: RTM_GETROUTE: truncated %lu to %lu bytes, retrying\n",
+                  (unsigned long)ssize, (unsigned long)bufsize));
+        /* try again with larger buffer */
+    }
+
+    ndefrts = rtmon_check_defaults(buf, (size_t)ssize);
+    free(buf);
+
+    if (ndefrts == 0) {
+        DPRINTF(("rtmon: no IPv6 default routes found\n"));
+    }
+    else {
+        DPRINTF(("rtmon: %d IPv6 default route%s found\n",
+                 ndefrts,
+                 ndefrts == 1 || ndefrts == -1 ? "" : "s"));
+    }
+
+    return ndefrts;
+}
+
+
+/**
+ * Scan netlink message in the buffer for IPv6 default route changes.
+ */
+static int
+rtmon_check_defaults(const void *buf, size_t len)
+{
+    struct nlmsghdr *nh;
+    int dfltdiff = 0;
+
+    for (nh = (struct nlmsghdr *)buf;
+         NLMSG_OK(nh, len);
+         nh = NLMSG_NEXT(nh, len))
+    {
+        struct rtmsg *rtm;
+        struct rtattr *rta;
+        int attrlen;
+        int delta = 0;
+        const void *gwbuf;
+        size_t gwlen;
+        int oif;
+
+        DPRINTF2(("nlmsg seq %d type %d flags 0x%x\n",
+                  nh->nlmsg_seq, nh->nlmsg_type, nh->nlmsg_flags));
+
+        if (nh->nlmsg_type == NLMSG_DONE) {
+            break;
+        }
+
+        if (nh->nlmsg_type == NLMSG_ERROR) {
+            struct nlmsgerr *ne = (struct nlmsgerr *)NLMSG_DATA(nh);
+            DPRINTF2(("> error %d\n", ne->error));
+            LWIP_UNUSED_ARG(ne);
+            break;
+        }
+
+        if (nh->nlmsg_type < RTM_BASE || RTM_MAX <= nh->nlmsg_type) {
+            /* shouldn't happen */
+            DPRINTF2(("> not an RTM message!\n"));
+            continue;
+        }
+
+
+        rtm = (struct rtmsg *)NLMSG_DATA(nh);
+        attrlen = RTM_PAYLOAD(nh);
+
+        if (nh->nlmsg_type == RTM_NEWROUTE) {
+            delta = +1;
+        }
+        else if (nh->nlmsg_type == RTM_DELROUTE) {
+            delta = -1;
+        }
+        else {
+            /* shouldn't happen */
+            continue;
+        }
+
+        /*
+         * Is this an IPv6 default route in the main table?  (Local
+         * table always has ::/0 reject route, hence the last check).
+         */
+        if (rtm->rtm_family == AF_INET6 /* should always be true */
+            && rtm->rtm_dst_len == 0
+            && rtm->rtm_table == RT_TABLE_MAIN)
+        {
+            dfltdiff += delta;
+        }
+        else {
+            /* some other route change */
+            continue;
+        }
+
+
+        gwbuf = NULL;
+        gwlen = 0;
+        oif = -1;
+
+        for (rta = RTM_RTA(rtm);
+             RTA_OK(rta, attrlen);
+             rta = RTA_NEXT(rta, attrlen))
+        {
+            if (rta->rta_type == RTA_GATEWAY) {
+                gwbuf = RTA_DATA(rta);
+                gwlen = RTA_PAYLOAD(rta);
+            }
+            else if (rta->rta_type == RTA_OIF) {
+                /* assert RTA_PAYLOAD(rta) == 4 */
+                memcpy(&oif, RTA_DATA(rta), sizeof(oif));
+            }
+        }
+
+        /* XXX: TODO: note that { oif, gw } was added/removed */
+        LWIP_UNUSED_ARG(gwbuf);
+        LWIP_UNUSED_ARG(gwlen);
+        LWIP_UNUSED_ARG(oif);
+    }
+
+    return dfltdiff;
+}
diff --git a/src/VBox/NetworkServices/NAT/rtmon_win.c b/src/VBox/NetworkServices/NAT/rtmon_win.c
new file mode 100644
index 00000000..7ceb431b
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/rtmon_win.c
@@ -0,0 +1,31 @@
+/* $Id: rtmon_win.c $ */
+/** @file
+ * NAT Network - IPv6 default route monitor for Windows.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+int
+rtmon_get_defaults(void) {
+    return 0;
+}
diff --git a/src/VBox/NetworkServices/NAT/tftp.h b/src/VBox/NetworkServices/NAT/tftp.h
new file mode 100644
index 00000000..7e8d67b4
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/tftp.h
@@ -0,0 +1,59 @@
+/* $Id: tftp.h $ */
+/** @file
+ * NAT Network - Definitions for TFTP protocol.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#ifndef VBOX_INCLUDED_SRC_NAT_tftp_h
+#define VBOX_INCLUDED_SRC_NAT_tftp_h
+#ifndef RT_WITHOUT_PRAGMA_ONCE
+# pragma once
+#endif
+
+#define TFTP_SERVER_PORT 69
+
+/* opcodes */
+#define TFTP_RRQ    1
+#define TFTP_WRQ    2
+#define TFTP_DATA   3
+#define TFTP_ACK    4
+#define TFTP_ERROR  5
+/* RFC 2347 */
+#define TFTP_OACK   6
+
+
+/* error codes */
+#define TFTP_EUNDEF     0 /* Not defined, see error message (if any). */
+#define TFTP_ENOENT     1 /* File not found. */
+#define TFTP_EACCESS    2 /* Access violation. */
+#define TFTP_EFBIG      3 /* Disk full or allocation exceeded. */
+#define TFTP_ENOSYS     4 /* Illegal TFTP operation. */
+#define TFTP_ESRCH      5 /* Unknown transfer ID. */
+#define TFTP_EEXIST     6 /* File already exists. */
+#define TFTP_EUSER      7 /* No such user. */
+/* RFC 2347 */
+#define TFTP_EONAK      8 /* Option refused. */
+
+
+#endif /* !VBOX_INCLUDED_SRC_NAT_tftp_h */
diff --git a/src/VBox/NetworkServices/NAT/winpoll.h b/src/VBox/NetworkServices/NAT/winpoll.h
new file mode 100644
index 00000000..5223946d
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/winpoll.h
@@ -0,0 +1,63 @@
+/* $Id: winpoll.h $ */
+/** @file
+ * NAT Network - poll(2) for winsock, definitions and declarations.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#ifndef VBOX_INCLUDED_SRC_NAT_winpoll_h
+#define VBOX_INCLUDED_SRC_NAT_winpoll_h
+#ifndef RT_WITHOUT_PRAGMA_ONCE
+# pragma once
+#endif
+# include <iprt/cdefs.h>
+/**
+ * WinSock2 has definition for POLL* and pollfd, but it defined for _WIN32_WINNT > 0x0600
+ * and used in WSAPoll, which has very unclear history.
+ */
+# if(_WIN32_WINNT < 0x0600)
+#  define POLLRDNORM  0x0100
+#  define POLLRDBAND  0x0200
+#  define POLLIN      (POLLRDNORM | POLLRDBAND)
+#  define POLLPRI     0x0400
+
+#  define POLLWRNORM  0x0010
+#  define POLLOUT     (POLLWRNORM)
+#  define POLLWRBAND  0x0020
+
+#  define POLLERR     0x0001
+#  define POLLHUP     0x0002
+#  define POLLNVAL    0x0004
+
+struct pollfd {
+
+    SOCKET  fd;
+    SHORT   events;
+    SHORT   revents;
+
+};
+#endif
+RT_C_DECLS_BEGIN
+int RTWinPoll(struct pollfd *pFds, unsigned int nfds, int timeout, int *pNready);
+RT_C_DECLS_END
+#endif /* !VBOX_INCLUDED_SRC_NAT_winpoll_h */
diff --git a/src/VBox/NetworkServices/NAT/winutils.h b/src/VBox/NetworkServices/NAT/winutils.h
new file mode 100644
index 00000000..be34680a
--- /dev/null
+++ b/src/VBox/NetworkServices/NAT/winutils.h
@@ -0,0 +1,220 @@
+/* $Id: winutils.h $ */
+/** @file
+ * NAT Network - winsock compatibility shim.
+ */
+
+/*
+ * Copyright (C) 2013-2023 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#ifndef VBOX_INCLUDED_SRC_NAT_winutils_h
+#define VBOX_INCLUDED_SRC_NAT_winutils_h
+#ifndef RT_WITHOUT_PRAGMA_ONCE
+# pragma once
+#endif
+
+# include <iprt/cdefs.h>
+
+# ifdef RT_OS_WINDOWS
+#  include <iprt/win/winsock2.h>
+#  include <iprt/win/ws2tcpip.h>
+#  include <mswsock.h>
+#  include <iprt/win/windows.h>
+#  include <iprt/err.h>
+#  include <iprt/net.h>
+#  include <iprt/log.h>
+/**
+ * Inclusion of lwip/def.h was added here to avoid conflict of definitions
+ * of hton-family functions in LWIP and windock's headers.
+ */
+#  include <lwip/def.h>
+
+#  ifndef PF_LOCAL
+#   define PF_LOCAL AF_INET
+#  endif
+
+#  ifdef DEBUG
+#   define err(code,...) do { \
+      AssertMsgFailed((__VA_ARGS__));           \
+    }while(0)
+#else
+#   define err(code,...) do { \
+      DPRINTF0((__VA_ARGS__));    \
+      ExitProcess(code); \
+    }while(0)
+#endif
+#  define errx err
+#  define __func__ __FUNCTION__
+#  define __attribute__(x) /* IGNORE */
+
+#  define SOCKERRNO()          (WSAGetLastError())
+#  define SET_SOCKERRNO(error) do { WSASetLastError(error); } while (0)
+
+/**
+ * "Windows Sockets Error Codes" obtained with WSAGetLastError().
+ * http://msdn.microsoft.com/en-us/library/windows/desktop/ms740668(v=vs.85).aspx
+ *
+ * This block of error codes from <winsock2.h> conflicts with "POSIX
+ * supplement" error codes from <errno.h>, but we don't expect to ever
+ * encounter the latter in the proxy code, so redefine them to their
+ * unixy names.
+ */
+#  undef  EWOULDBLOCK
+#  define EWOULDBLOCK           WSAEWOULDBLOCK
+#  undef  EINPROGRESS
+#  define EINPROGRESS           WSAEINPROGRESS
+#  undef  EALREADY
+#  define EALREADY              WSAEALREADY
+#  undef  ENOTSOCK
+#  define ENOTSOCK              WSAENOTSOCK
+#  undef  EDESTADDRREQ
+#  define EDESTADDRREQ          WSAEDESTADDRREQ
+#  undef  EMSGSIZE
+#  define EMSGSIZE              WSAEMSGSIZE
+#  undef  EPROTOTYPE
+#  define EPROTOTYPE            WSAEPROTOTYPE
+#  undef  ENOPROTOOPT
+#  define ENOPROTOOPT           WSAENOPROTOOPT
+#  undef  EPROTONOSUPPORT
+#  define EPROTONOSUPPORT       WSAEPROTONOSUPPORT
+#  undef  ESOCKTNOSUPPORT
+#  define ESOCKTNOSUPPORT       WSAESOCKTNOSUPPORT
+#  undef  EOPNOTSUPP
+#  define EOPNOTSUPP            WSAEOPNOTSUPP
+#  undef  EPFNOSUPPORT
+#  define EPFNOSUPPORT          WSAEPFNOSUPPORT
+#  undef  EAFNOSUPPORT
+#  define EAFNOSUPPORT          WSAEAFNOSUPPORT
+#  undef  EADDRINUSE
+#  define EADDRINUSE            WSAEADDRINUSE
+#  undef  EADDRNOTAVAIL
+#  define EADDRNOTAVAIL         WSAEADDRNOTAVAIL
+#  undef  ENETDOWN
+#  define ENETDOWN              WSAENETDOWN
+#  undef  ENETUNREACH
+#  define ENETUNREACH           WSAENETUNREACH
+#  undef  ENETRESET
+#  define ENETRESET             WSAENETRESET
+#  undef  ECONNABORTED
+#  define ECONNABORTED          WSAECONNABORTED
+#  undef  ECONNRESET
+#  define ECONNRESET            WSAECONNRESET
+#  undef  ENOBUFS
+#  define ENOBUFS               WSAENOBUFS
+#  undef  EISCONN
+#  define EISCONN               WSAEISCONN
+#  undef  ENOTCONN
+#  define ENOTCONN              WSAENOTCONN
+#  undef  ESHUTDOWN
+#  define ESHUTDOWN             WSAESHUTDOWN
+#  undef  ETOOMANYREFS
+#  define ETOOMANYREFS          WSAETOOMANYREFS
+#  undef  ETIMEDOUT
+#  define ETIMEDOUT             WSAETIMEDOUT
+#  undef  ECONNREFUSED
+#  define ECONNREFUSED          WSAECONNREFUSED
+#  undef  ELOOP
+#  define ELOOP                 WSAELOOP
+#  undef  ENAMETOOLONG
+#  define ENAMETOOLONG          WSAENAMETOOLONG
+#  undef  EHOSTDOWN
+#  define EHOSTDOWN             WSAEHOSTDOWN
+#  undef  EHOSTUNREACH
+#  define EHOSTUNREACH          WSAEHOSTUNREACH
+
+/**
+ * parameters to shutdown (2) with Winsock2
+ * http://msdn.microsoft.com/en-us/library/windows/desktop/ms740481(v=vs.85).aspx
+ */
+#  define SHUT_RD SD_RECEIVE
+#  define SHUT_WR SD_SEND
+#  define SHUT_RDWR SD_BOTH
+
+typedef ULONG nfds_t;
+
+typedef WSABUF IOVEC;
+
+#  define IOVEC_GET_BASE(iov) ((iov).buf)
+#  define IOVEC_SET_BASE(iov, b) ((iov).buf = (b))
+
+#  define IOVEC_GET_LEN(iov) ((iov).len)
+#  define IOVEC_SET_LEN(iov, l) ((iov).len = (ULONG)(l))
+
+#if _WIN32_WINNT < 0x0600
+/* otherwise defined the other way around in ws2def.h */
+#define cmsghdr _WSACMSGHDR
+
+#undef CMSG_DATA       /* wincrypt.h can byte my shiny metal #undef */
+#define CMSG_DATA WSA_CMSG_DATA
+#define CMSG_LEN WSA_CMSG_LEN
+#define CMSG_SPACE WSA_CMSG_SPACE
+
+#define CMSG_FIRSTHDR WSA_CMSG_FIRSTHDR
+#define CMSG_NXTHDR WSA_CMSG_NXTHDR
+#endif  /* _WIN32_WINNT < 0x0600 - provide unglified CMSG names */
+
+RT_C_DECLS_BEGIN
+int RTWinSocketPair(int domain, int type, int protocol, SOCKET socket_vector[2]);
+RT_C_DECLS_END
+
+# else /* !RT_OS_WINDOWS */
+
+#  include <errno.h>
+#  include <unistd.h>
+
+#  define SOCKET int
+#  define INVALID_SOCKET (-1)
+#  define SOCKET_ERROR (-1)
+
+#  define SOCKERRNO()          (errno)
+#  define SET_SOCKERRNO(error) do { errno = (error); } while (0)
+
+#  define closesocket(s) close(s)
+#  define ioctlsocket(s, req, arg) ioctl((s), (req), (arg))
+
+typedef struct iovec IOVEC;
+
+#  define IOVEC_GET_BASE(iov) ((iov).iov_base)
+#  define IOVEC_SET_BASE(iov, b) ((iov).iov_base = (b))
+
+#  define IOVEC_GET_LEN(iov) ((iov).iov_len)
+#  define IOVEC_SET_LEN(iov, l) ((iov).iov_len = (l))
+# endif
+
+DECLINLINE(int)
+proxy_error_is_transient(int error)
+{
+# if !defined(RT_OS_WINDOWS)
+    return error == EWOULDBLOCK
+#  if EAGAIN != EWOULDBLOCK
+        || error == EAGAIN
+#  endif
+        || error == EINTR
+        || error == ENOBUFS
+        || error == ENOMEM;
+# else
+    return error == WSAEWOULDBLOCK
+        || error == WSAEINTR    /* NB: we don't redefine EINTR above */
+        || error == WSAENOBUFS;
+# endif
+}
+
+#endif /* !VBOX_INCLUDED_SRC_NAT_winutils_h */