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-.\" This man page is Copyright (C) 1999 Andi Kleen <ak@muc.de>.
-.\"
-.\" %%%LICENSE_START(VERBATIM_ONE_PARA)
-.\" Permission is granted to distribute possibly modified copies
-.\" of this page provided the header is included verbatim,
-.\" and in case of nontrivial modification author and date
-.\" of the modification is added to the header.
-.\" %%%LICENSE_END
-.\"
-.\" $Id: icmp.7,v 1.6 2000/08/14 08:03:45 ak Exp $
-.\"
-.TH ICMP 7 2012-05-10 "Linux" "Linux Programmer's Manual"
-.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.
-.LP
-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 2.4.9)"
-.\" Precisely: from 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 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 2.4.9)"
-.\" Precisely: from 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 2.6.28-rc4 Documentation/networking/ip-sysctl.txt
-If disabled, ICMP error messages are sent with the primary address of
-the exiting interface.
-
-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.
-
-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 2.1.32
-.\" The following taken from 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 2.4.9)"
-.\" Precisely: from 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 2.6.28-rc4 Documentation/networking/ip-sysctl.txt
-Limit the maximum rates for sending ICMP packets whose type matches
-.IR 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 2.6.28-rc4 Documentation/networking/ip-sysctl.txt
-Mask made of ICMP types for which rates are being limited.
-
-Significant bits: IHGFEDCBA9876543210
-.br
-Default mask: 0000001100000011000 (0x1818)
-
-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
-
-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 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.
-.SH VERSIONS
-Support for the
-.B ICMP_ADDRESS
-request was removed in 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)
-.PP
-RFC\ 792 for a description of the ICMP protocol.
-.SH COLOPHON
-This page is part of release 3.79 of the Linux
-.I man-pages
-project.
-A description of the project,
-information about reporting bugs,
-and the latest version of this page,
-can be found at
-\%http://www.kernel.org/doc/man\-pages/.
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