ICMP(7)                UNIX System V(Internet Utilities)                ICMP(7)


NAME
      ICMP - Internet Control Message Protocol

SYNOPSIS
      #include <sys/socket.h>
      #include <netinet/in.h>
      #include <netinet/ipicmp.h>

      s = socket(AFINET, SOCKRAW, proto);

      t = topen("/dev/icmp", ORDWR);

DESCRIPTION
      ICMP is the error and control message protocol used by the Internet
      protocol family.  It is used by the kernel to handle and report errors in
      protocol processing.  It may also be accessed by programs using the
      socket interface or the Transport Level Interface (TLI) for network
      monitoring and diagnostic functions.  When used with the socket
      interface, a raw socket type is used.  The protocol number for ICMP, used
      in the proto parameter to the socket call, can be obtained from
      getprotobyname() [see getprotoent(3N)].  ICMP file descriptors and
      sockets are connectionless, and are normally used with the tsndudata /
      trcvudata and the sendto() / recvfrom() calls.

      Outgoing packets automatically have an Internet Protocol (IP) header
      prepended to them.  Incoming packets are provided to the user with the IP
      header and options intact.

      ICMP is an datagram protocol layered above IP. It is used internally by
      the protcol code for various purposes including routing, fault isolation,
      and congestion control.  Receipt of an ICMP redirect message will add a
      new entry in the routing table, or modify an existing one.  ICMP messages
      are routinely sent by the protocol code.  Received ICMP messages may be
      reflected back to users of higher-level protocols such as TCP or UDP as
      error returns from system calls.  A copy of all ICMP message received by
      the system is provided to every holder of an open ICMP socket or TLI
      descriptor.

SEE ALSO
      send(2), getprotoent(3N), recvfrom(3N), trcvudata(3N), tsndudata(3N),
      routing(4), inet(7), ip(7)

      Postel, Jon, .IR "Internet Control Message Protocol - DARPA Internet
      Program Protocol Specification" , RFC 792, Network Information Center,
      SRI International, Menlo Park, Calif., September 1981

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

      EISCONN             An attempt was made to establish a connection on a
                          socket which already has one, or when trying to send
                          a datagram with the destination address specified and


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ICMP(7)                UNIX System V(Internet Utilities)                ICMP(7)


                          the socket is already connected.

      ENOTCONN            An attempt was made to send a datagram, but no
                          destination address is specified, and the socket has
                          not been connected.

      ENOBUFS             The system ran out of memory for an internal data
                          structure.

      EADDRNOTAVAIL       An attempt was made to create a socket with a network
                          address for which no network interface exists.

NOTES
      Replies to ICMP echo messages which are source routed are not sent back
      using inverted source routes, but rather go back through the normal
      routing mechanisms.






































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