icmp(7)                                                             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 inter-
     face, a "raw socket" type is used. The protocol number for ICMP, used
     in the proto parameter to the socket call, can be obtained from get-
     protobyname() [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 iso-
     lation, 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.

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 the
                    socket is already connected.

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

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



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icmp(7)                                                             icmp(7)

     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 nor-
     mal routing mechanisms.

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

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







































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