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