1.\" Copyright (c) 1986, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)icmp.4 8.1 (Berkeley) 6/5/93 29.\" $FreeBSD: src/share/man/man4/icmp.4,v 1.7.2.4 2001/12/17 11:30:12 ru Exp $ 30.\" $DragonFly: src/share/man/man4/icmp.4,v 1.2 2003/06/17 04:36:59 dillon Exp $ 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/types.h 40.In sys/socket.h 41.In netinet/in.h 42.Ft int 43.Fn socket AF_INET SOCK_RAW proto 44.Sh DESCRIPTION 45.Tn ICMP 46is the error and control message protocol used 47by 48.Tn IP 49and the Internet protocol family. It may be accessed 50through a 51.Dq raw socket 52for network monitoring 53and diagnostic functions. 54The 55.Fa proto 56parameter to the socket call to create an 57.Tn ICMP 58socket 59is obtained from 60.Xr getprotobyname 3 . 61.Tn ICMP 62sockets are connectionless, 63and are normally used with the 64.Xr sendto 2 65and 66.Xr recvfrom 2 67calls, though the 68.Xr connect 2 69call may also be used to fix the destination for future 70packets (in which case the 71.Xr read 2 72or 73.Xr recv 2 74and 75.Xr write 2 76or 77.Xr send 2 78system calls may be used). 79.Pp 80Outgoing packets automatically have an 81.Tn IP 82header prepended to 83them (based on the destination address). 84Incoming packets are received with the 85.Tn IP 86header and options intact. 87.Sh ERRORS 88A socket operation may fail with one of the following errors returned: 89.Bl -tag -width Er 90.It Bq Er EISCONN 91when trying to establish a connection on a socket which 92already has one, or when trying to send a datagram with the destination 93address specified and the socket is already connected; 94.It Bq Er ENOTCONN 95when trying to send a datagram, but 96no destination address is specified, and the socket hasn't been 97connected; 98.It Bq Er ENOBUFS 99when the system runs out of memory for 100an internal data structure; 101.It Bq Er EADDRNOTAVAIL 102when an attempt is made to create a 103socket with a network address for which no network interface 104exists. 105.El 106.Sh SEE ALSO 107.Xr recv 2 , 108.Xr send 2 , 109.Xr inet 4 , 110.Xr intro 4 , 111.Xr ip 4 112.Sh HISTORY 113The 114.Nm 115protocol appeared in 116.Bx 4.3 . 117