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

NAME
       icmp - Linux IPv4 ICMP kernel module.

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.

       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 packets passed to the socket can be filtered using the ICMP_FILTER socket option.  ICMP packets 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 addresses.

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

       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 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.

       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 Linux 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 above).

       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.

       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.

VERSIONS
       Support for the ICMP_ADDRESS request was removed in 2.2.

       Support for ICMP_SOURCE_QUENCH was removed in Linux 2.2.

NOTES
       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 accepted only 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 netstat(8) output with a zero inode.

SEE ALSO
       ip(7), rdisc(8)

       RFC 792 for a description of the ICMP protocol.

Linux                                                                          2017-11-26                                                                        ICMP(7)