ICMP(4)                   386BSD Programmer's Manual                   ICMP(4)

NAME
     icmp - Internet Control Message Protocol

SYNOPSIS
     Makefile:
     $(NONSTDINC) += $(INCNET)
     C:
     #include <sys/socket.h>
     #include "in.h"

     int
     socket(AF_INET, SOCK_RAW, proto)

DESCRIPTION
     ICMP is the error and control message protocol used by IP and the
     Internet 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 and recvfrom 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.

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
                      connected;

     [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
                      network address for which no network interface exists.

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

HISTORY
     The icmp protocol appeared in 4.3BSD.

4.3 Berkeley Distribution       March 28, 1991                               1