ICMP(7)                                                      ICMP(7)


       NAME
             ICMP - Internet Control Message Protocol

       SYNOPSIS
             icmp

       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 t_sndudata / t_rcvudata and the sendto /
             recvfrom calls [see send(3N) and recv(3N)].

             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 a datagram protocol layered above IP.  It is used
             internally by the protocol 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 messages received by the system is provided to every
             holder of an open ICMP socket or TLI descriptor.

       REFERENCES
             getprotoent(3N), inet(7), IP(7), recv(3N), routing(4),
             send(3N), t_rcvudata(3N), t_sndudata(3N)
             RFC 792

       NOTICES
             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.




                           Copyright 1994 Novell, Inc.               Page 1