ICMP(7)                          (TCP/IP)                           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, 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:




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   ICMP(7)                          (TCP/IP)                           ICMP(7)


         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 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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