1.\" $NetBSD: icmp.4,v 1.7 2002/02/13 08:17:35 ross 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. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" @(#)icmp.4 8.1 (Berkeley) 6/5/93 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.Fd #include \*[Lt]sys/socket.h\*[Gt] 44.Fd #include \*[Lt]netinet/in.h\*[Gt] 45.Ft int 46.Fn socket AF_INET SOCK_RAW proto 47.Sh DESCRIPTION 48.Tn ICMP 49is the error and control message protocol used 50by 51.Tn IP 52and the Internet protocol family. 53It may be accessed through a 54.Dq raw socket 55for network monitoring and diagnostic functions. 56The 57.Fa proto 58parameter to the socket call to create an 59.Tn ICMP 60socket is obtained from 61.Xr getprotobyname 3 . 62.Tn ICMP 63sockets are connectionless, and 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 packets 70(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 them (based on the destination address). 83Incoming packets are received with the 84.Tn IP 85header and options intact. 86.Sh DIAGNOSTICS 87A socket operation may fail with one of the following errors returned: 88.Bl -tag -width [EADDRNOTAVAIL] 89.It Bq Er EISCONN 90when trying to establish a connection on a socket which 91already has one, or when trying to send a datagram with the destination 92address specified and the socket is already connected; 93.It Bq Er ENOTCONN 94when trying to send a datagram, but 95no destination address is specified, and the socket hasn't been 96connected; 97.It Bq Er ENOBUFS 98when the system runs out of memory for 99an internal data structure; 100.It Bq Er EADDRNOTAVAIL 101when an attempt is made to create a 102socket with a network address for which no network interface exists. 103.El 104.Sh SEE ALSO 105.Xr recv 2 , 106.Xr send 2 , 107.Xr inet 4 , 108.Xr intro 4 , 109.Xr ip 4 110.Rs 111.%R RFC 112.%N 792 113.%D September 1981 114.%T "Internet Control Message Protocol" 115.Re 116.Rs 117.%R RFC 118.%N 1122 119.%D October 1989 120.%T "Requirements for Internet Hosts -- Communication Layers" 121.Re 122.Sh HISTORY 123The 124.Nm 125protocol appeared in 126.Bx 4.3 . 127