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ICMP(4)                  BSD Kernel Interfaces Manual                  ICMP(4)

NAME
     icmp -- Internet Control Message Protocol

SYNOPSIS
     #include <&lt;sys/socket.h>&gt;
     #include <&lt;netinet/in.h>&gt;

     int
     socket(AF_INET, SOCK_RAW, proto);

DESCRIPTION
     ICMP is the error and control message protocol used by IP and the Inter-
     net protocol family.  It may be accessed through a ``raw socket'' for
     network monitoring and diagnostic functions.  The proto parameter to the
     socket call to create an ICMP socket is obtained from getprotobyname(3).
     ICMP sockets are connectionless, and are normally used with the sendto(2)
     and recvfrom(2) calls, though the connect(2) call may also be used to fix
     the destination for future packets (in which case the read(2) or recv(2)
     and write(2) or send(2) system calls may be used).

     Outgoing packets automatically have an IP header prepended to them (based
     on the destination address).  Incoming packets are received with the IP
     header and options intact.

   Types
     ICMP messages are classified according to the type and code fields
     present in the ICMP header.  The abbreviations for the types and codes
     may be used in rules in pf.conf(5).  The following types are defined:

           Num    Abbrev.       Description
           0      echorep       Echo reply
           3      unreach       Destination unreachable
           4      squench       Packet loss, slow down
           5      redir         Shorter route exists
           6      althost       Alternate host address
           8      echoreq       Echo request
           9      routeradv     Router advertisement
           10     routersol     Router solicitation
           11     timex         Time exceeded
           12     paramprob     Invalid IP header
           13     timereq       Timestamp request
           14     timerep       Timestamp reply
           15     inforeq       Information request
           16     inforep       Information reply
           17     maskreq       Address mask request
           18     maskrep       Address mask reply
           30     trace         Traceroute
           31     dataconv      Data conversion problem
           32     mobredir      Mobile host redirection
           33     ipv6-where    IPv6 where-are-you
           34     ipv6-here     IPv6 i-am-here
           35     mobregreq     Mobile registration request
           36     mobregrep     Mobile registration reply
           39     skip          SKIP
           40     photuris      Photuris

     The following codes are defined:

           Num    Abbrev.           Type         Description
           0      net-unr           unreach      Network unreachable
           1      host-unr          unreach      Host unreachable
           2      proto-unr         unreach      Protocol unreachable
           3      port-unr          unreach      Port unreachable
           4      needfrag          unreach      Fragmentation needed but DF
                                                                bit set
           5      srcfail           unreach      Source routing failed
           6      net-unk           unreach      Network unknown
           7      host-unk          unreach      Host unknown
           8      isolate           unreach      Host isolated
           9      net-prohib        unreach      Network administratively
                                                                prohibited
           10     host-prohib       unreach      Host administratively
                                                                prohibited
           11     net-tos           unreach      Invalid TOS for network
           12     host-tos          unreach      Invalid TOS for host
           13     filter-prohib     unreach      Prohibited access
           14     host-preced       unreach      Precedence violation
           15     cutoff-preced     unreach      Precedence cutoff
           0      redir-net         redir        Shorter route for network
           1      redir-host        redir        Shorter route for host
           2      redir-tos-net     redir        Shorter route for TOS and
                                                                network
           3      redir-tos-host    redir        Shorter route for TOS and
                                                                host
           0      normal-adv        routeradv    Normal advertisement
           16     common-adv        routeradv    Selective advertisement
           0      transit           timex        Time exceeded in transit
           1      reassemb          timex        Time exceeded in reassembly
           0      badhead           paramprob    Invalid option pointer
           1      optmiss           paramprob    Missing option
           2      badlen            paramprob    Invalid length
           1      unknown-ind       photuris     Unknown security index
           2      auth-fail         photuris     Authentication failed
           3      decrypt-fail      photuris     Decryption failed

DIAGNOSTICS
     A socket operation may fail with one of the following errors returned:

     [EISCONN]        when trying to establish a connection on a socket which
                      already has one, or when trying to send a datagram with
                      the destination address specified and the socket is
                      already connected;

     [ENOTCONN]       when trying to send a datagram, but no destination
                      address is specified, and the socket hasn't been con-
                      nected;

     [ENOBUFS]        when the system runs out of memory for an internal data
                      structure;

     [EADDRNOTAVAIL]  when an attempt is made to create a socket with a net-
                      work address for which no network interface exists.

SEE ALSO
     recv(2), send(2), inet(4), ip(4), netintro(4)

HISTORY
     The icmp protocol appeared in 4.3BSD.

BSD                             April 27, 2017                             BSD