icmp

       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 open-
       ing  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 pack-
              ets 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  compli-

       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,  inclu-
              sive) 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.

       may appear in netstat(8) output with a zero inode.

SEE ALSO
       ip(7)

       RFC 792 for a description of the ICMP protocol.

COLOPHON
       This page is part of release 4.04 of the Linux  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/.

Linux                             2015-04-19                           ICMP(7)
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