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Linux 2.6 - man page for ipproto_icmp (linux section 7)

ICMP(7) 			    Linux Programmer's Manual				  ICMP(7)

       icmp, IPPROTO_ICMP - Linux IPv4 ICMP kernel module.

       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 mod-
       ule also answers ICMP requests.

       A  user	protocol  may  receive ICMP packets for all local sockets by opening a raw socket
       with the protocol IPPROTO_ICMP.	See raw(7) for more information.  The types of ICMP pack-
       ets  passed to the socket can be filtered using the ICMP_FILTER socket option.  ICMP pack-
       ets are always processed by the kernel too, even when passed to a user socket.

       Linux limits the rate of ICMP  error  packets  to  each	destination.   ICMP_REDIRECT  and
       ICMP_DEST_UNREACH are also limited by the destination route of the incoming packets.

   /proc interfaces
       ICMP  supports  a  set  of  /proc  interfaces to configure some global IP parameters.  The
       parameters  can	be  accessed   by   reading   or   writing   files   in   the	directory
       /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.  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.

       icmp_destunreach_rate (Linux 2.2 to 2.4.9)
	      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 ICMP_FRAG_NEEDED packets needed for path MTU discovery.

       icmp_echo_ignore_all (since Linux 2.2)
	      If this value is nonzero, Linux will ignore all ICMP_ECHO requests.

       icmp_echo_ignore_broadcasts (since Linux 2.2)
	      If this value is nonzero, Linux will ignore all ICMP_ECHO packets sent to broadcast

       icmp_echoreply_rate (Linux 2.2 to 2.4.9)
	      Maximum  rate  for  sending  ICMP_ECHOREPLY packets in response to ICMP_ECHOREQUEST

       icmp_errors_use_inbound_ifaddr (Boolean; default: disabled; since Linux 2.6.12)
	      If disabled, ICMP error messages are sent with the primary address of  the  exiting

	      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 com-
	      plicated 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.

       icmp_ignore_bogus_error_responses (Boolean; default: disabled; since Linux 2.2)
	      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.

       icmp_paramprob_rate (Linux 2.2 to 2.4.9)
	      Maximum rate for sending ICMP_PARAMETERPROB packets.  These packets are sent when a
	      packet arrives with an invalid IP header.

       icmp_ratelimit (integer; default: 1000; since Linux 2.4.10)
	      Limit  the  maximum rates for sending ICMP packets whose type matches icmp_ratemask
	      (see below) to specific targets.	0 to disable any limiting, otherwise the  minimum
	      space between responses in milliseconds.

       icmp_ratemask (integer; default: see below; since Linux 2.4.10)
	      Mask made of ICMP types for which rates are being limited.

	      Significant bits: IHGFEDCBA9876543210
	      Default mask:	0000001100000011000 (0x1818)

	      Bit definitions (see the kernel source file include/linux/icmp.h):

		  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

	      The  bits marked with an asterisk are rate limited by default (see the default mask

       icmp_timeexceed_rate (Linux 2.2 to 2.4.9)
	      Maximum rate for sending ICMP_TIME_EXCEEDED packets.  These  packets  are  sent  to
	      prevent loops when a packet has crossed too many hops.

       Support for the ICMP_ADDRESS request was removed in 2.2.

       Support for ICMP_SOURCE_QUENCH was removed in Linux 2.2.

       As  many other implementations don't support IPPROTO_ICMP raw sockets, this feature should
       not be relied on in portable programs.

       ICMP_REDIRECT packets are not sent when Linux is not acting as a router.   They	are  also
       only  accepted  from  the old gateway defined in the routing table and the redirect routes
       are expired after some time.

       The 64-bit timestamp returned by  ICMP_TIMESTAMP  is  in  milliseconds  since  the  Epoch,
       1970-01-01 00:00:00 +0000 (UTC).

       Linux ICMP internally uses a raw socket to send ICMPs.  This raw socket may appear in net-
       stat(8) output with a zero inode.


       RFC 792 for a description of the ICMP protocol.

       This page is part of release 3.27 of the Linux man-pages project.  A  description  of  the
       project,   and	information  about  reporting  bugs,  can  be  found  at  http://www.ker-

Linux					    2010-02-25					  ICMP(7)

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