1.\" $OpenBSD: icmp.4,v 1.13 2011/09/03 22:59:07 jmc Exp $ 2.\" $NetBSD: icmp.4,v 1.3 1994/11/30 16:22:14 jtc Exp $ 3.\" 4.\" Copyright (c) 1986, 1991, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" @(#)icmp.4 8.1 (Berkeley) 6/5/93 32.\" 33.Dd $Mdocdate: September 3 2011 $ 34.Dt ICMP 4 35.Os 36.Sh NAME 37.Nm icmp 38.Nd Internet Control Message Protocol 39.Sh SYNOPSIS 40.Fd #include <sys/socket.h> 41.Fd #include <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. 50It may be accessed through 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.Ss Types 88ICMP messages are classified according to the type and code fields 89present in the ICMP header. 90The abbreviations for the types and codes may be used in rules in 91.Xr pf.conf 5 . 92The following types are defined: 93.Bl -column "Num" "ipv6-where" -offset indent 94.It Sy Num Ta Sy "Abbrev." Ta Sy Description 95.It 0 Ta echorep Ta "Echo reply" 96.It 3 Ta unreach Ta "Destination unreachable" 97.It 4 Ta squench Ta "Packet loss, slow down" 98.It 5 Ta redir Ta "Shorter route exists" 99.It 6 Ta althost Ta "Alternate host address" 100.It 8 Ta echoreq Ta "Echo request" 101.It 9 Ta routeradv Ta "Router advertisement" 102.It 10 Ta routersol Ta "Router solicitation" 103.It 11 Ta timex Ta "Time exceeded" 104.It 12 Ta paramprob Ta "Invalid IP header" 105.It 13 Ta timereq Ta "Timestamp request" 106.It 14 Ta timerep Ta "Timestamp reply" 107.It 15 Ta inforeq Ta "Information request" 108.It 16 Ta inforep Ta "Information reply" 109.It 17 Ta maskreq Ta "Address mask request" 110.It 18 Ta maskrep Ta "Address mask reply" 111.It 30 Ta trace Ta "Traceroute" 112.It 31 Ta dataconv Ta "Data conversion problem" 113.It 32 Ta mobredir Ta "Mobile host redirection" 114.It 33 Ta ipv6-where Ta "IPv6 where-are-you" 115.It 34 Ta ipv6-here Ta "IPv6 i-am-here" 116.It 35 Ta mobregreq Ta "Mobile registration request" 117.It 36 Ta mobregrep Ta "Mobile registration reply" 118.It 39 Ta skip Ta "SKIP" 119.It 40 Ta photuris Ta "Photuris" 120.El 121.Pp 122The following codes are defined: 123.Bl -column "Num" "redir-tos-host" "paramprob" "Description" -offset indent 124.It Sy Num Ta Sy "Abbrev." Ta Sy Type Ta Sy Description 125.It 0 Ta net-unr Ta unreach Ta "Network unreachable" 126.It 1 Ta host-unr Ta unreach Ta "Host unreachable" 127.It 2 Ta proto-unr Ta unreach Ta "Protocol unreachable" 128.It 3 Ta port-unr Ta unreach Ta "Port unreachable" 129.It 4 Ta needfrag Ta unreach Ta "Fragmentation needed but DF bit set" 130.It 5 Ta srcfail Ta unreach Ta "Source routing failed" 131.It 6 Ta net-unk Ta unreach Ta "Network unknown" 132.It 7 Ta host-unk Ta unreach Ta "Host unknown" 133.It 8 Ta isolate Ta unreach Ta "Host isolated" 134.It 9 Ta net-prohib Ta unreach Ta "Network administratively prohibited" 135.It 10 Ta host-prohib Ta unreach Ta "Host administratively prohibited" 136.It 11 Ta net-tos Ta unreach Ta "Invalid TOS for network" 137.It 12 Ta host-tos Ta unreach Ta "Invalid TOS for host" 138.It 13 Ta filter-prohib Ta unreach Ta "Prohibited access" 139.It 14 Ta host-preced Ta unreach Ta "Precedence violation" 140.It 15 Ta cutoff-preced Ta unreach Ta "Precedence cutoff" 141.It 0 Ta redir-net Ta redir Ta "Shorter route for network" 142.It 1 Ta redir-host Ta redir Ta "Shorter route for host" 143.It 2 Ta redir-tos-net Ta redir Ta "Shorter route for TOS and network" 144.It 3 Ta redir-tos-host Ta redir Ta "Shorter route for TOS and host" 145.It 0 Ta normal-adv Ta routeradv Ta "Normal advertisement" 146.It 16 Ta common-adv Ta routeradv Ta "Selective advertisement" 147.It 0 Ta transit Ta timex Ta "Time exceeded in transit" 148.It 1 Ta reassemb Ta timex Ta "Time exceeded in reassembly" 149.It 0 Ta badhead Ta paramprob Ta "Invalid option pointer" 150.It 1 Ta optmiss Ta paramprob Ta "Missing option" 151.It 2 Ta badlen Ta paramprob Ta "Invalid length" 152.It 1 Ta unknown-ind Ta photuris Ta "Unknown security index" 153.It 2 Ta auth-fail Ta photuris Ta "Authentication failed" 154.It 3 Ta decrypt-fail Ta photuris Ta "Decryption failed" 155.El 156.Sh DIAGNOSTICS 157A socket operation may fail with one of the following errors returned: 158.Bl -tag -width [EADDRNOTAVAIL] 159.It Bq Er EISCONN 160when trying to establish a connection on a socket which 161already has one, or when trying to send a datagram with the destination 162address specified and the socket is already connected; 163.It Bq Er ENOTCONN 164when trying to send a datagram, but 165no destination address is specified, and the socket hasn't been 166connected; 167.It Bq Er ENOBUFS 168when the system runs out of memory for 169an internal data structure; 170.It Bq Er EADDRNOTAVAIL 171when an attempt is made to create a 172socket with a network address for which no network interface 173exists. 174.El 175.Sh SEE ALSO 176.Xr recv 2 , 177.Xr send 2 , 178.Xr inet 4 , 179.Xr ip 4 , 180.Xr netintro 4 181.Sh HISTORY 182The 183.Nm 184protocol appeared in 185.Bx 4.3 . 186