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diff --git a/man7/icmp.7 b/man7/icmp.7 new file mode 100644 index 0000000..cd54614 --- /dev/null +++ b/man7/icmp.7 @@ -0,0 +1,196 @@ +'\" t +.\" SPDX-License-Identifier: Linux-man-pages-1-para +.\" +.\" This man page is Copyright (C) 1999 Andi Kleen <ak@muc.de>. +.\" +.\" $Id: icmp.7,v 1.6 2000/08/14 08:03:45 ak Exp $ +.\" +.TH icmp 7 2023-07-15 "Linux man-pages 6.05.01" +.SH NAME +icmp \- Linux IPv4 ICMP kernel module. +.SH DESCRIPTION +This kernel protocol module implements the Internet Control +Message Protocol defined in RFC\ 792. +It is used to signal error conditions and for diagnosis. +The user doesn't interact directly with this module; +instead it communicates with the other protocols in the kernel +and these pass the ICMP errors to the application layers. +The kernel ICMP module also answers ICMP requests. +.PP +A user protocol may receive ICMP packets for all local sockets by opening +a raw socket with the protocol +.BR IPPROTO_ICMP . +See +.BR raw (7) +for more information. +The types of ICMP packets passed to the socket can be filtered using the +.B ICMP_FILTER +socket option. +ICMP packets are always processed by the kernel too, even +when passed to a user socket. +.PP +Linux limits the rate of ICMP error packets to each destination. +.B ICMP_REDIRECT +and +.B ICMP_DEST_UNREACH +are also limited by the destination route of the incoming packets. +.SS /proc interfaces +ICMP supports a set of +.I /proc +interfaces to configure some global IP parameters. +The parameters can be accessed by reading or writing files in the directory +.IR /proc/sys/net/ipv4/ . +Most of these parameters are rate limitations for specific ICMP types. +Linux 2.2 uses a token bucket filter to limit ICMPs. +.\" FIXME . better description needed +The value is the timeout in jiffies until the token bucket filter is +cleared after a burst. +A jiffy is a system dependent unit, usually 10ms on i386 and +about 1ms on alpha and ia64. +.TP +.IR icmp_destunreach_rate " (Linux 2.2 to Linux 2.4.9)" +.\" Precisely: from Linux 2.1.102 +Maximum rate to send ICMP Destination Unreachable packets. +This limits the rate at which packets are sent to any individual +route or destination. +The limit does not affect sending of +.B ICMP_FRAG_NEEDED +packets needed for path MTU discovery. +.TP +.IR icmp_echo_ignore_all " (since Linux 2.2)" +.\" Precisely: 2.1.68 +If this value is nonzero, Linux will ignore all +.B ICMP_ECHO +requests. +.TP +.IR icmp_echo_ignore_broadcasts " (since Linux 2.2)" +.\" Precisely: from Linux 2.1.68 +If this value is nonzero, Linux will ignore all +.B ICMP_ECHO +packets sent to broadcast addresses. +.TP +.IR icmp_echoreply_rate " (Linux 2.2 to Linux 2.4.9)" +.\" Precisely: from Linux 2.1.102 +Maximum rate for sending +.B ICMP_ECHOREPLY +packets in response to +.B ICMP_ECHOREQUEST +packets. +.TP +.IR icmp_errors_use_inbound_ifaddr " (Boolean; default: disabled; since Linux 2.6.12)" +.\" The following taken from Linux 2.6.28-rc4 Documentation/networking/ip-sysctl.txt +If disabled, ICMP error messages are sent with the primary address of +the exiting interface. +.IP +If enabled, the message will be sent with the primary address of +the interface that received the packet that caused the ICMP error. +This is the behavior that many network administrators will expect from +a router. +And it can make debugging complicated network layouts much easier. +.IP +Note that if no primary address exists for the interface selected, +then the primary address of the first non-loopback interface that +has one will be used regardless of this setting. +.TP +.IR icmp_ignore_bogus_error_responses " (Boolean; default: disabled; since Linux 2.2)" +.\" precisely: since Linux 2.1.32 +.\" The following taken from Linux 2.6.28-rc4 Documentation/networking/ip-sysctl.txt +Some routers violate RFC1122 by sending bogus responses to broadcast frames. +Such violations are normally logged via a kernel warning. +If this parameter is enabled, the kernel will not give such warnings, +which will avoid log file clutter. +.TP +.IR icmp_paramprob_rate " (Linux 2.2 to Linux 2.4.9)" +.\" Precisely: from Linux 2.1.102 +Maximum rate for sending +.B ICMP_PARAMETERPROB +packets. +These packets are sent when a packet arrives with an invalid IP header. +.TP +.IR icmp_ratelimit " (integer; default: 1000; since Linux 2.4.10)" +.\" The following taken from Linux 2.6.28-rc4 Documentation/networking/ip-sysctl.txt +Limit the maximum rates for sending ICMP packets whose type matches +.I icmp_ratemask +(see below) to specific targets. +0 to disable any limiting, +otherwise the minimum space between responses in milliseconds. +.TP +.IR icmp_ratemask " (integer; default: see below; since Linux 2.4.10)" +.\" The following taken from Linux 2.6.28-rc4 Documentation/networking/ip-sysctl.txt +Mask made of ICMP types for which rates are being limited. +.IP +Significant bits: IHGFEDCBA9876543210 +.br +Default mask: 0000001100000011000 (0x1818) +.IP +Bit definitions (see the Linux kernel source file +.IR include/linux/icmp.h ): +.RS 12 +.TS +l l. +0 Echo Reply +3 Destination Unreachable * +4 Source Quench * +5 Redirect +8 Echo Request +B Time Exceeded * +C Parameter Problem * +D Timestamp Request +E Timestamp Reply +F Info Request +G Info Reply +H Address Mask Request +I Address Mask Reply +.TE +.RE +.PP +The bits marked with an asterisk are rate limited by default +(see the default mask above). +.TP +.IR icmp_timeexceed_rate " (Linux 2.2 to Linux 2.4.9)" +Maximum rate for sending +.B ICMP_TIME_EXCEEDED +packets. +These packets are +sent to prevent loops when a packet has crossed too many hops. +.TP +.IR ping_group_range " (two integers; default: see below; since Linux 2.6.39)" +Range of the group IDs (minimum and maximum group IDs, inclusive) +that are allowed to create ICMP Echo sockets. +The default is "1 0", which +means no group is allowed to create ICMP Echo sockets. +.SH VERSIONS +Support for the +.B ICMP_ADDRESS +request was removed in Linux 2.2. +.PP +Support for +.B ICMP_SOURCE_QUENCH +was removed in Linux 2.2. +.SH NOTES +As many other implementations don't support +.B IPPROTO_ICMP +raw sockets, this feature +should not be relied on in portable programs. +.\" not really true ATM +.\" .PP +.\" Linux ICMP should be compliant to RFC 1122. +.PP +.B ICMP_REDIRECT +packets are not sent when Linux is not acting as a router. +They are also accepted only from the old gateway defined in the +routing table and the redirect routes are expired after some time. +.PP +The 64-bit timestamp returned by +.B ICMP_TIMESTAMP +is in milliseconds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC). +.PP +Linux ICMP internally uses a raw socket to send ICMPs. +This raw socket may appear in +.BR netstat (8) +output with a zero inode. +.SH SEE ALSO +.BR ip (7), +.BR rdisc (8) +.PP +RFC\ 792 for a description of the ICMP protocol. |