icmp

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 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 pa-
       rameters.   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  un-
       til  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  re-
              quests.

       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  ad-
              dress 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  er-
              ror.  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 se-
              lected, then the primary address of the first  non-loopback  in-
              terface 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 re-
              sponses 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   in-
              clude/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.

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.

COLOPHON
       This page is part of release 5.05 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
       https://www.kernel.org/doc/man-pages/.

Linux                             2017-11-26                           ICMP(7)