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. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)icmp.4 8.1 (Berkeley) 6/5/93 33.\" $FreeBSD: src/share/man/man4/icmp.4,v 1.7.2.4 2001/12/17 11:30:12 ru Exp $ 34.\" $DragonFly: src/share/man/man4/icmp.4,v 1.2 2003/06/17 04:36:59 dillon Exp $ 35.\" 36.Dd June 5, 1993 37.Dt ICMP 4 38.Os 39.Sh NAME 40.Nm icmp 41.Nd Internet Control Message Protocol 42.Sh SYNOPSIS 43.In sys/types.h 44.In sys/socket.h 45.In netinet/in.h 46.Ft int 47.Fn socket AF_INET SOCK_RAW proto 48.Sh DESCRIPTION 49.Tn ICMP 50is the error and control message protocol used 51by 52.Tn IP 53and the Internet protocol family. It may be accessed 54through a 55.Dq raw socket 56for network monitoring 57and diagnostic functions. 58The 59.Fa proto 60parameter to the socket call to create an 61.Tn ICMP 62socket 63is obtained from 64.Xr getprotobyname 3 . 65.Tn ICMP 66sockets are connectionless, 67and are normally used with the 68.Xr sendto 2 69and 70.Xr recvfrom 2 71calls, though the 72.Xr connect 2 73call may also be used to fix the destination for future 74packets (in which case the 75.Xr read 2 76or 77.Xr recv 2 78and 79.Xr write 2 80or 81.Xr send 2 82system calls may be used). 83.Pp 84Outgoing packets automatically have an 85.Tn IP 86header prepended to 87them (based on the destination address). 88Incoming packets are received with the 89.Tn IP 90header and options intact. 91.Sh ERRORS 92A socket operation may fail with one of the following errors returned: 93.Bl -tag -width Er 94.It Bq Er EISCONN 95when trying to establish a connection on a socket which 96already has one, or when trying to send a datagram with the destination 97address specified and the socket is already connected; 98.It Bq Er ENOTCONN 99when trying to send a datagram, but 100no destination address is specified, and the socket hasn't been 101connected; 102.It Bq Er ENOBUFS 103when the system runs out of memory for 104an internal data structure; 105.It Bq Er EADDRNOTAVAIL 106when an attempt is made to create a 107socket with a network address for which no network interface 108exists. 109.El 110.Sh SEE ALSO 111.Xr recv 2 , 112.Xr send 2 , 113.Xr inet 4 , 114.Xr intro 4 , 115.Xr ip 4 116.Sh HISTORY 117The 118.Nm 119protocol appeared in 120.Bx 4.3 . 121