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.\" $Id$ 34.\" 35.Dd June 5, 1993 36.Dt ICMP 4 37.Os BSD 4.3 38.Sh NAME 39.Nm icmp 40.Nd Internet Control Message Protocol 41.Sh SYNOPSIS 42.Fd #include <sys/socket.h> 43.Fd #include <netinet/in.h> 44.Ft int 45.Fn socket AF_INET SOCK_RAW proto 46.Sh DESCRIPTION 47.Tn ICMP 48is the error and control message protocol used 49by 50.Tn IP 51and the Internet protocol family. It may be accessed 52through a 53.Dq raw socket 54for network monitoring 55and diagnostic functions. 56The 57.Fa proto 58parameter to the socket call to create an 59.Tn ICMP 60socket 61is obtained from 62.Xr getprotobyname 3 . 63.Tn ICMP 64sockets are connectionless, 65and are normally used with the 66.Xr sendto 2 67and 68.Xr recvfrom 2 69calls, though the 70.Xr connect 2 71call may also be used to fix the destination for future 72packets (in which case the 73.Xr read 2 74or 75.Xr recv 2 76and 77.Xr write 2 78or 79.Xr send 2 80system calls may be used). 81.Pp 82Outgoing packets automatically have an 83.Tn IP 84header prepended to 85them (based on the destination address). 86Incoming packets are received with the 87.Tn IP 88header and options intact. 89.Sh DIAGNOSTICS 90A socket operation may fail with one of the following errors returned: 91.Bl -tag -width [EADDRNOTAVAIL] 92.It Bq Er EISCONN 93when trying to establish a connection on a socket which 94already has one, or when trying to send a datagram with the destination 95address specified and the socket is already connected; 96.It Bq Er ENOTCONN 97when trying to send a datagram, but 98no destination address is specified, and the socket hasn't been 99connected; 100.It Bq Er ENOBUFS 101when the system runs out of memory for 102an internal data structure; 103.It Bq Er EADDRNOTAVAIL 104when an attempt is made to create a 105socket with a network address for which no network interface 106exists. 107.El 108.Sh SEE ALSO 109.Xr recv 2 , 110.Xr send 2 , 111.Xr inet 4 , 112.Xr intro 4 , 113.Xr ip 4 114.Sh HISTORY 115The 116.Nm 117protocol appeared in 118.Bx 4.3 . 119