.\" Copyright (c) 1986, 1991, 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)icmp.4 8.1 (Berkeley) 6/5/93 .\" $FreeBSD: src/share/man/man4/icmp.4,v 1.7.2.4 2001/12/17 11:30:12 ru Exp $ .\" $DragonFly: src/share/man/man4/icmp.4,v 1.2 2003/06/17 04:36:59 dillon Exp $ .\" .Dd June 5, 1993 .Dt ICMP 4 .Os .Sh NAME .Nm icmp .Nd Internet Control Message Protocol .Sh SYNOPSIS .In sys/types.h .In sys/socket.h .In netinet/in.h .Ft int .Fn socket AF_INET SOCK_RAW proto .Sh DESCRIPTION .Tn ICMP is the error and control message protocol used by .Tn IP and the Internet protocol family. It may be accessed through a .Dq raw socket for network monitoring and diagnostic functions. The .Fa proto parameter to the socket call to create an .Tn ICMP socket is obtained from .Xr getprotobyname 3 . .Tn ICMP sockets are connectionless, and are normally used with the .Xr sendto 2 and .Xr recvfrom 2 calls, though the .Xr connect 2 call may also be used to fix the destination for future packets (in which case the .Xr read 2 or .Xr recv 2 and .Xr write 2 or .Xr send 2 system calls may be used). .Pp Outgoing packets automatically have an .Tn IP header prepended to them (based on the destination address). Incoming packets are received with the .Tn IP header and options intact. .Sh ERRORS A socket operation may fail with one of the following errors returned: .Bl -tag -width Er .It Bq Er 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; .It Bq Er ENOTCONN when trying to send a datagram, but no destination address is specified, and the socket hasn't been connected; .It Bq Er ENOBUFS when the system runs out of memory for an internal data structure; .It Bq Er EADDRNOTAVAIL when an attempt is made to create a socket with a network address for which no network interface exists. .El .Sh SEE ALSO .Xr recv 2 , .Xr send 2 , .Xr inet 4 , .Xr intro 4 , .Xr ip 4 .Sh HISTORY The .Nm protocol appeared in .Bx 4.3 .