# SPDX-License-Identifier: GPL-2.0-only # # IP configuration # config IP_MULTICAST bool "IP: multicasting" help This is code for addressing several networked computers at once, enlarging your kernel by about 2 KB. You need multicasting if you intend to participate in the MBONE, a high bandwidth network on top of the Internet which carries audio and video broadcasts. More information about the MBONE is on the WWW at . For most people, it's safe to say N. config IP_ADVANCED_ROUTER bool "IP: advanced router" help If you intend to run your Linux box mostly as a router, i.e. as a computer that forwards and redistributes network packets, say Y; you will then be presented with several options that allow more precise control about the routing process. The answer to this question won't directly affect the kernel: answering N will just cause the configurator to skip all the questions about advanced routing. Note that your box can only act as a router if you enable IP forwarding in your kernel; you can do that by saying Y to "/proc file system support" and "Sysctl support" below and executing the line echo "1" > /proc/sys/net/ipv4/ip_forward at boot time after the /proc file system has been mounted. If you turn on IP forwarding, you should consider the rp_filter, which automatically rejects incoming packets if the routing table entry for their source address doesn't match the network interface they're arriving on. This has security advantages because it prevents the so-called IP spoofing, however it can pose problems if you use asymmetric routing (packets from you to a host take a different path than packets from that host to you) or if you operate a non-routing host which has several IP addresses on different interfaces. To turn rp_filter on use: echo 1 > /proc/sys/net/ipv4/conf//rp_filter or echo 1 > /proc/sys/net/ipv4/conf/all/rp_filter Note that some distributions enable it in startup scripts. For details about rp_filter strict and loose mode read . If unsure, say N here. config IP_FIB_TRIE_STATS bool "FIB TRIE statistics" depends on IP_ADVANCED_ROUTER help Keep track of statistics on structure of FIB TRIE table. Useful for testing and measuring TRIE performance. config IP_MULTIPLE_TABLES bool "IP: policy routing" depends on IP_ADVANCED_ROUTER select FIB_RULES help Normally, a router decides what to do with a received packet based solely on the packet's final destination address. If you say Y here, the Linux router will also be able to take the packet's source address into account. Furthermore, the TOS (Type-Of-Service) field of the packet can be used for routing decisions as well. If you need more information, see the Linux Advanced Routing and Traffic Control documentation at If unsure, say N. config IP_ROUTE_MULTIPATH bool "IP: equal cost multipath" depends on IP_ADVANCED_ROUTER help Normally, the routing tables specify a single action to be taken in a deterministic manner for a given packet. If you say Y here however, it becomes possible to attach several actions to a packet pattern, in effect specifying several alternative paths to travel for those packets. The router considers all these paths to be of equal "cost" and chooses one of them in a non-deterministic fashion if a matching packet arrives. config IP_ROUTE_VERBOSE bool "IP: verbose route monitoring" depends on IP_ADVANCED_ROUTER help If you say Y here, which is recommended, then the kernel will print verbose messages regarding the routing, for example warnings about received packets which look strange and could be evidence of an attack or a misconfigured system somewhere. The information is handled by the klogd daemon which is responsible for kernel messages ("man klogd"). config IP_ROUTE_CLASSID bool config IP_PNP bool "IP: kernel level autoconfiguration" help This enables automatic configuration of IP addresses of devices and of the routing table during kernel boot, based on either information supplied on the kernel command line or by BOOTP or RARP protocols. You need to say Y only for diskless machines requiring network access to boot (in which case you want to say Y to "Root file system on NFS" as well), because all other machines configure the network in their startup scripts. config IP_PNP_DHCP bool "IP: DHCP support" depends on IP_PNP help If you want your Linux box to mount its whole root file system (the one containing the directory /) from some other computer over the net via NFS and you want the IP address of your computer to be discovered automatically at boot time using the DHCP protocol (a special protocol designed for doing this job), say Y here. In case the boot ROM of your network card was designed for booting Linux and does DHCP itself, providing all necessary information on the kernel command line, you can say N here. If unsure, say Y. Note that if you want to use DHCP, a DHCP server must be operating on your network. Read for details. config IP_PNP_BOOTP bool "IP: BOOTP support" depends on IP_PNP help If you want your Linux box to mount its whole root file system (the one containing the directory /) from some other computer over the net via NFS and you want the IP address of your computer to be discovered automatically at boot time using the BOOTP protocol (a special protocol designed for doing this job), say Y here. In case the boot ROM of your network card was designed for booting Linux and does BOOTP itself, providing all necessary information on the kernel command line, you can say N here. If unsure, say Y. Note that if you want to use BOOTP, a BOOTP server must be operating on your network. Read for details. config IP_PNP_RARP bool "IP: RARP support" depends on IP_PNP help If you want your Linux box to mount its whole root file system (the one containing the directory /) from some other computer over the net via NFS and you want the IP address of your computer to be discovered automatically at boot time using the RARP protocol (an older protocol which is being obsoleted by BOOTP and DHCP), say Y here. Note that if you want to use RARP, a RARP server must be operating on your network. Read for details. config NET_IPIP tristate "IP: tunneling" select INET_TUNNEL select NET_IP_TUNNEL help Tunneling means encapsulating data of one protocol type within another protocol and sending it over a channel that understands the encapsulating protocol. This particular tunneling driver implements encapsulation of IP within IP, which sounds kind of pointless, but can be useful if you want to make your (or some other) machine appear on a different network than it physically is, or to use mobile-IP facilities (allowing laptops to seamlessly move between networks without changing their IP addresses). Saying Y to this option will produce two modules ( = code which can be inserted in and removed from the running kernel whenever you want). Most people won't need this and can say N. config NET_IPGRE_DEMUX tristate "IP: GRE demultiplexer" help This is helper module to demultiplex GRE packets on GRE version field criteria. Required by ip_gre and pptp modules. config NET_IP_TUNNEL tristate select DST_CACHE select GRO_CELLS default n config NET_IPGRE tristate "IP: GRE tunnels over IP" depends on (IPV6 || IPV6=n) && NET_IPGRE_DEMUX select NET_IP_TUNNEL help Tunneling means encapsulating data of one protocol type within another protocol and sending it over a channel that understands the encapsulating protocol. This particular tunneling driver implements GRE (Generic Routing Encapsulation) and at this time allows encapsulating of IPv4 or IPv6 over existing IPv4 infrastructure. This driver is useful if the other endpoint is a Cisco router: Cisco likes GRE much better than the other Linux tunneling driver ("IP tunneling" above). In addition, GRE allows multicast redistribution through the tunnel. config NET_IPGRE_BROADCAST bool "IP: broadcast GRE over IP" depends on IP_MULTICAST && NET_IPGRE help One application of GRE/IP is to construct a broadcast WAN (Wide Area Network), which looks like a normal Ethernet LAN (Local Area Network), but can be distributed all over the Internet. If you want to do that, say Y here and to "IP multicast routing" below. config IP_MROUTE_COMMON bool depends on IP_MROUTE || IPV6_MROUTE config IP_MROUTE bool "IP: multicast routing" depends on IP_MULTICAST select IP_MROUTE_COMMON help This is used if you want your machine to act as a router for IP packets that have several destination addresses. It is needed on the MBONE, a high bandwidth network on top of the Internet which carries audio and video broadcasts. In order to do that, you would most likely run the program mrouted. If you haven't heard about it, you don't need it. config IP_MROUTE_MULTIPLE_TABLES bool "IP: multicast policy routing" depends on IP_MROUTE && IP_ADVANCED_ROUTER select FIB_RULES help Normally, a multicast router runs a userspace daemon and decides what to do with a multicast packet based on the source and destination addresses. If you say Y here, the multicast router will also be able to take interfaces and packet marks into account and run multiple instances of userspace daemons simultaneously, each one handling a single table. If unsure, say N. config IP_PIMSM_V1 bool "IP: PIM-SM version 1 support" depends on IP_MROUTE help Kernel side support for Sparse Mode PIM (Protocol Independent Multicast) version 1. This multicast routing protocol is used widely because Cisco supports it. You need special software to use it (pimd-v1). Please see for more information about PIM. Say Y if you want to use PIM-SM v1. Note that you can say N here if you just want to use Dense Mode PIM. config IP_PIMSM_V2 bool "IP: PIM-SM version 2 support" depends on IP_MROUTE help Kernel side support for Sparse Mode PIM version 2. In order to use this, you need an experimental routing daemon supporting it (pimd or gated-5). This routing protocol is not used widely, so say N unless you want to play with it. config SYN_COOKIES bool "IP: TCP syncookie support" help Normal TCP/IP networking is open to an attack known as "SYN flooding". This denial-of-service attack prevents legitimate remote users from being able to connect to your computer during an ongoing attack and requires very little work from the attacker, who can operate from anywhere on the Internet. SYN cookies provide protection against this type of attack. If you say Y here, the TCP/IP stack will use a cryptographic challenge protocol known as "SYN cookies" to enable legitimate users to continue to connect, even when your machine is under attack. There is no need for the legitimate users to change their TCP/IP software; SYN cookies work transparently to them. For technical information about SYN cookies, check out . If you are SYN flooded, the source address reported by the kernel is likely to have been forged by the attacker; it is only reported as an aid in tracing the packets to their actual source and should not be taken as absolute truth. SYN cookies may prevent correct error reporting on clients when the server is really overloaded. If this happens frequently better turn them off. If you say Y here, you can disable SYN cookies at run time by saying Y to "/proc file system support" and "Sysctl support" below and executing the command echo 0 > /proc/sys/net/ipv4/tcp_syncookies after the /proc file system has been mounted. If unsure, say N. config NET_IPVTI tristate "Virtual (secure) IP: tunneling" depends on IPV6 || IPV6=n select INET_TUNNEL select NET_IP_TUNNEL select XFRM help Tunneling means encapsulating data of one protocol type within another protocol and sending it over a channel that understands the encapsulating protocol. This can be used with xfrm mode tunnel to give the notion of a secure tunnel for IPSEC and then use routing protocol on top. config NET_UDP_TUNNEL tristate select NET_IP_TUNNEL default n config NET_FOU tristate "IP: Foo (IP protocols) over UDP" select NET_UDP_TUNNEL help Foo over UDP allows any IP protocol to be directly encapsulated over UDP include tunnels (IPIP, GRE, SIT). By encapsulating in UDP network mechanisms and optimizations for UDP (such as ECMP and RSS) can be leveraged to provide better service. config NET_FOU_IP_TUNNELS bool "IP: FOU encapsulation of IP tunnels" depends on NET_IPIP || NET_IPGRE || IPV6_SIT select NET_FOU help Allow configuration of FOU or GUE encapsulation for IP tunnels. When this option is enabled IP tunnels can be configured to use FOU or GUE encapsulation. config INET_AH tristate "IP: AH transformation" select XFRM_AH help Support for IPsec AH (Authentication Header). AH can be used with various authentication algorithms. Besides enabling AH support itself, this option enables the generic implementations of the algorithms that RFC 8221 lists as MUST be implemented. If you need any other algorithms, you'll need to enable them in the crypto API. You should also enable accelerated implementations of any needed algorithms when available. If unsure, say Y. config INET_ESP tristate "IP: ESP transformation" select XFRM_ESP help Support for IPsec ESP (Encapsulating Security Payload). ESP can be used with various encryption and authentication algorithms. Besides enabling ESP support itself, this option enables the generic implementations of the algorithms that RFC 8221 lists as MUST be implemented. If you need any other algorithms, you'll need to enable them in the crypto API. You should also enable accelerated implementations of any needed algorithms when available. If unsure, say Y. config INET_ESP_OFFLOAD tristate "IP: ESP transformation offload" depends on INET_ESP select XFRM_OFFLOAD default n help Support for ESP transformation offload. This makes sense only if this system really does IPsec and want to do it with high throughput. A typical desktop system does not need it, even if it does IPsec. If unsure, say N. config INET_ESPINTCP bool "IP: ESP in TCP encapsulation (RFC 8229)" depends on XFRM && INET_ESP select STREAM_PARSER select NET_SOCK_MSG select XFRM_ESPINTCP help Support for RFC 8229 encapsulation of ESP and IKE over TCP/IPv4 sockets. If unsure, say N. config INET_IPCOMP tristate "IP: IPComp transformation" select INET_XFRM_TUNNEL select XFRM_IPCOMP help Support for IP Payload Compression Protocol (IPComp) (RFC3173), typically needed for IPsec. If unsure, say Y. config INET_TABLE_PERTURB_ORDER int "INET: Source port perturbation table size (as power of 2)" if EXPERT default 16 help Source port perturbation table size (as power of 2) for RFC 6056 3.3.4. Algorithm 4: Double-Hash Port Selection Algorithm. The default is almost always what you want. Only change this if you know what you are doing. config INET_XFRM_TUNNEL tristate select INET_TUNNEL default n config INET_TUNNEL tristate default n config INET_DIAG tristate "INET: socket monitoring interface" default y help Support for INET (TCP, DCCP, etc) socket monitoring interface used by native Linux tools such as ss. ss is included in iproute2, currently downloadable at: http://www.linuxfoundation.org/collaborate/workgroups/networking/iproute2 If unsure, say Y. config INET_TCP_DIAG depends on INET_DIAG def_tristate INET_DIAG config INET_UDP_DIAG tristate "UDP: socket monitoring interface" depends on INET_DIAG && (IPV6 || IPV6=n) default n help Support for UDP socket monitoring interface used by the ss tool. If unsure, say Y. config INET_RAW_DIAG tristate "RAW: socket monitoring interface" depends on INET_DIAG && (IPV6 || IPV6=n) default n help Support for RAW socket monitoring interface used by the ss tool. If unsure, say Y. config INET_DIAG_DESTROY bool "INET: allow privileged process to administratively close sockets" depends on INET_DIAG default n help Provides a SOCK_DESTROY operation that allows privileged processes (e.g., a connection manager or a network administration tool such as ss) to close sockets opened by other processes. Closing a socket in this way interrupts any blocking read/write/connect operations on the socket and causes future socket calls to behave as if the socket had been disconnected. If unsure, say N. menuconfig TCP_CONG_ADVANCED bool "TCP: advanced congestion control" help Support for selection of various TCP congestion control modules. Nearly all users can safely say no here, and a safe default selection will be made (CUBIC with new Reno as a fallback). If unsure, say N. if TCP_CONG_ADVANCED config TCP_CONG_BIC tristate "Binary Increase Congestion (BIC) control" default m help BIC-TCP is a sender-side only change that ensures a linear RTT fairness under large windows while offering both scalability and bounded TCP-friendliness. The protocol combines two schemes called additive increase and binary search increase. When the congestion window is large, additive increase with a large increment ensures linear RTT fairness as well as good scalability. Under small congestion windows, binary search increase provides TCP friendliness. See http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/ config TCP_CONG_CUBIC tristate "CUBIC TCP" default y help This is version 2.0 of BIC-TCP which uses a cubic growth function among other techniques. See http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/cubic-paper.pdf config TCP_CONG_WESTWOOD tristate "TCP Westwood+" default m help TCP Westwood+ is a sender-side only modification of the TCP Reno protocol stack that optimizes the performance of TCP congestion control. It is based on end-to-end bandwidth estimation to set congestion window and slow start threshold after a congestion episode. Using this estimation, TCP Westwood+ adaptively sets a slow start threshold and a congestion window which takes into account the bandwidth used at the time congestion is experienced. TCP Westwood+ significantly increases fairness wrt TCP Reno in wired networks and throughput over wireless links. config TCP_CONG_HTCP tristate "H-TCP" default m help H-TCP is a send-side only modifications of the TCP Reno protocol stack that optimizes the performance of TCP congestion control for high speed network links. It uses a modeswitch to change the alpha and beta parameters of TCP Reno based on network conditions and in a way so as to be fair with other Reno and H-TCP flows. config TCP_CONG_HSTCP tristate "High Speed TCP" default n help Sally Floyd's High Speed TCP (RFC 3649) congestion control. A modification to TCP's congestion control mechanism for use with large congestion windows. A table indicates how much to increase the congestion window by when an ACK is received. For more detail see https://www.icir.org/floyd/hstcp.html config TCP_CONG_HYBLA tristate "TCP-Hybla congestion control algorithm" default n help TCP-Hybla is a sender-side only change that eliminates penalization of long-RTT, large-bandwidth connections, like when satellite legs are involved, especially when sharing a common bottleneck with normal terrestrial connections. config TCP_CONG_VEGAS tristate "TCP Vegas" default n help TCP Vegas is a sender-side only change to TCP that anticipates the onset of congestion by estimating the bandwidth. TCP Vegas adjusts the sending rate by modifying the congestion window. TCP Vegas should provide less packet loss, but it is not as aggressive as TCP Reno. config TCP_CONG_NV tristate "TCP NV" default n help TCP NV is a follow up to TCP Vegas. It has been modified to deal with 10G networks, measurement noise introduced by LRO, GRO and interrupt coalescence. In addition, it will decrease its cwnd multiplicatively instead of linearly. Note that in general congestion avoidance (cwnd decreased when # packets queued grows) cannot coexist with congestion control (cwnd decreased only when there is packet loss) due to fairness issues. One scenario when they can coexist safely is when the CA flows have RTTs << CC flows RTTs. For further details see http://www.brakmo.org/networking/tcp-nv/ config TCP_CONG_SCALABLE tristate "Scalable TCP" default n help Scalable TCP is a sender-side only change to TCP which uses a MIMD congestion control algorithm which has some nice scaling properties, though is known to have fairness issues. See http://www.deneholme.net/tom/scalable/ config TCP_CONG_LP tristate "TCP Low Priority" default n help TCP Low Priority (TCP-LP), a distributed algorithm whose goal is to utilize only the excess network bandwidth as compared to the ``fair share`` of bandwidth as targeted by TCP. See http://www-ece.rice.edu/networks/TCP-LP/ config TCP_CONG_VENO tristate "TCP Veno" default n help TCP Veno is a sender-side only enhancement of TCP to obtain better throughput over wireless networks. TCP Veno makes use of state distinguishing to circumvent the difficult judgment of the packet loss type. TCP Veno cuts down less congestion window in response to random loss packets. See config TCP_CONG_YEAH tristate "YeAH TCP" select TCP_CONG_VEGAS default n help YeAH-TCP is a sender-side high-speed enabled TCP congestion control algorithm, which uses a mixed loss/delay approach to compute the congestion window. It's design goals target high efficiency, internal, RTT and Reno fairness, resilience to link loss while keeping network elements load as low as possible. For further details look here: http://wil.cs.caltech.edu/pfldnet2007/paper/YeAH_TCP.pdf config TCP_CONG_ILLINOIS tristate "TCP Illinois" default n help TCP-Illinois is a sender-side modification of TCP Reno for high speed long delay links. It uses round-trip-time to adjust the alpha and beta parameters to achieve a higher average throughput and maintain fairness. For further details see: http://www.ews.uiuc.edu/~shaoliu/tcpillinois/index.html config TCP_CONG_DCTCP tristate "DataCenter TCP (DCTCP)" default n help DCTCP leverages Explicit Congestion Notification (ECN) in the network to provide multi-bit feedback to the end hosts. It is designed to provide: - High burst tolerance (incast due to partition/aggregate), - Low latency (short flows, queries), - High throughput (continuous data updates, large file transfers) with commodity, shallow-buffered switches. All switches in the data center network running DCTCP must support ECN marking and be configured for marking when reaching defined switch buffer thresholds. The default ECN marking threshold heuristic for DCTCP on switches is 20 packets (30KB) at 1Gbps, and 65 packets (~100KB) at 10Gbps, but might need further careful tweaking. For further details see: http://simula.stanford.edu/~alizade/Site/DCTCP_files/dctcp-final.pdf config TCP_CONG_CDG tristate "CAIA Delay-Gradient (CDG)" default n help CAIA Delay-Gradient (CDG) is a TCP congestion control that modifies the TCP sender in order to: o Use the delay gradient as a congestion signal. o Back off with an average probability that is independent of the RTT. o Coexist with flows that use loss-based congestion control. o Tolerate packet loss unrelated to congestion. For further details see: D.A. Hayes and G. Armitage. "Revisiting TCP congestion control using delay gradients." In Networking 2011. Preprint: http://goo.gl/No3vdg config TCP_CONG_BBR tristate "BBR TCP" default n help BBR (Bottleneck Bandwidth and RTT) TCP congestion control aims to maximize network utilization and minimize queues. It builds an explicit model of the bottleneck delivery rate and path round-trip propagation delay. It tolerates packet loss and delay unrelated to congestion. It can operate over LAN, WAN, cellular, wifi, or cable modem links. It can coexist with flows that use loss-based congestion control, and can operate with shallow buffers, deep buffers, bufferbloat, policers, or AQM schemes that do not provide a delay signal. It requires the fq ("Fair Queue") pacing packet scheduler. choice prompt "Default TCP congestion control" default DEFAULT_CUBIC help Select the TCP congestion control that will be used by default for all connections. config DEFAULT_BIC bool "Bic" if TCP_CONG_BIC=y config DEFAULT_CUBIC bool "Cubic" if TCP_CONG_CUBIC=y config DEFAULT_HTCP bool "Htcp" if TCP_CONG_HTCP=y config DEFAULT_HYBLA bool "Hybla" if TCP_CONG_HYBLA=y config DEFAULT_VEGAS bool "Vegas" if TCP_CONG_VEGAS=y config DEFAULT_VENO bool "Veno" if TCP_CONG_VENO=y config DEFAULT_WESTWOOD bool "Westwood" if TCP_CONG_WESTWOOD=y config DEFAULT_DCTCP bool "DCTCP" if TCP_CONG_DCTCP=y config DEFAULT_CDG bool "CDG" if TCP_CONG_CDG=y config DEFAULT_BBR bool "BBR" if TCP_CONG_BBR=y config DEFAULT_RENO bool "Reno" endchoice endif config TCP_CONG_CUBIC tristate depends on !TCP_CONG_ADVANCED default y config DEFAULT_TCP_CONG string default "bic" if DEFAULT_BIC default "cubic" if DEFAULT_CUBIC default "htcp" if DEFAULT_HTCP default "hybla" if DEFAULT_HYBLA default "vegas" if DEFAULT_VEGAS default "westwood" if DEFAULT_WESTWOOD default "veno" if DEFAULT_VENO default "reno" if DEFAULT_RENO default "dctcp" if DEFAULT_DCTCP default "cdg" if DEFAULT_CDG default "bbr" if DEFAULT_BBR default "cubic" config TCP_SIGPOOL tristate config TCP_AO bool "TCP: Authentication Option (RFC5925)" select CRYPTO select TCP_SIGPOOL depends on 64BIT && IPV6 != m # seq-number extension needs WRITE_ONCE(u64) help TCP-AO specifies the use of stronger Message Authentication Codes (MACs), protects against replays for long-lived TCP connections, and provides more details on the association of security with TCP connections than TCP MD5 (See RFC5925) If unsure, say N. config TCP_MD5SIG bool "TCP: MD5 Signature Option support (RFC2385)" select CRYPTO select CRYPTO_MD5 select TCP_SIGPOOL help RFC2385 specifies a method of giving MD5 protection to TCP sessions. Its main (only?) use is to protect BGP sessions between core routers on the Internet. If unsure, say N.