1.\" $NetBSD: icmp.4,v 1.9 2003/08/07 10:31:02 agc Exp $ 2.\" 3.\" Copyright (c) 1986, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" @(#)icmp.4 8.1 (Berkeley) 6/5/93 31.\" 32.Dd June 5, 1993 33.Dt ICMP 4 34.Os 35.Sh NAME 36.Nm icmp 37.Nd Internet Control Message Protocol 38.Sh SYNOPSIS 39.In sys/socket.h 40.In netinet/in.h 41.Ft int 42.Fn socket AF_INET SOCK_RAW proto 43.Sh DESCRIPTION 44.Tn ICMP 45is the error and control message protocol used 46by 47.Tn IP 48and the Internet protocol family. 49It may be accessed through a 50.Dq raw socket 51for network monitoring and diagnostic functions. 52The 53.Fa proto 54parameter to the socket call to create an 55.Tn ICMP 56socket is obtained from 57.Xr getprotobyname 3 . 58.Tn ICMP 59sockets are connectionless, and are normally used with the 60.Xr sendto 2 61and 62.Xr recvfrom 2 63calls, though the 64.Xr connect 2 65call may also be used to fix the destination for future packets 66(in which case the 67.Xr read 2 68or 69.Xr recv 2 70and 71.Xr write 2 72or 73.Xr send 2 74system calls may be used). 75.Pp 76Outgoing packets automatically have an 77.Tn IP 78header prepended to them (based on the destination address). 79Incoming packets are received with the 80.Tn IP 81header and options intact. 82.Sh DIAGNOSTICS 83A socket operation may fail with one of the following errors returned: 84.Bl -tag -width [EADDRNOTAVAIL] 85.It Bq Er EISCONN 86when trying to establish a connection on a socket which 87already has one, or when trying to send a datagram with the destination 88address specified and the socket is already connected; 89.It Bq Er ENOTCONN 90when trying to send a datagram, but 91no destination address is specified, and the socket hasn't been 92connected; 93.It Bq Er ENOBUFS 94when the system runs out of memory for 95an internal data structure; 96.It Bq Er EADDRNOTAVAIL 97when an attempt is made to create a 98socket with a network address for which no network interface exists. 99.El 100.Sh SEE ALSO 101.Xr recv 2 , 102.Xr send 2 , 103.Xr inet 4 , 104.Xr intro 4 , 105.Xr ip 4 106.Rs 107.%R RFC 108.%N 792 109.%D September 1981 110.%T "Internet Control Message Protocol" 111.Re 112.Rs 113.%R RFC 114.%N 1122 115.%D October 1989 116.%T "Requirements for Internet Hosts -- Communication Layers" 117.Re 118.Sh HISTORY 119The 120.Nm 121protocol appeared in 122.Bx 4.3 . 123