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Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)icmp.4 8.1 (Berkeley) 6/5/93 29.\" $FreeBSD$ 30.\" 31.Dd September 30, 2014 32.Dt ICMP 4 33.Os 34.Sh NAME 35.Nm icmp 36.Nd Internet Control Message Protocol 37.Sh SYNOPSIS 38.In sys/types.h 39.In sys/socket.h 40.In netinet/in.h 41.Ft int 42.Fn socket AF_INET SOCK_RAW proto 43.Sh DESCRIPTION 44.Tn ICMP 45is the error and control message protocol used 46by 47.Tn IP 48and the Internet protocol family. 49It may be accessed 50through 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 x xxxxxxxxxxxx -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 x xxxxxxxxxxxx xxxxxxxx -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.Ss MIB Variables 157The 158.Tn ICMP 159protocol implements a number of variables in the 160.Va net.inet.icmp 161branch of the 162.Xr sysctl 3 163MIB. 164.Bl -tag -width ".Va icmplim_output" 165.It Va maskrepl 166.Pq Vt boolean 167Enable/disable replies to ICMP Address Mask Request packets. 168Defaults to false. 169.It Va maskfake 170.Pq Vt "unsigned integer" 171When 172.Va maskrepl 173is set and this value is non-zero, 174it will be used instead of the real address mask when 175the system replies to an ICMP Address Mask Request packet. 176Defaults to 0. 177.It Va icmplim 178.Pq Vt integer 179Bandwidth limit for ICMP replies in packets/second. 180Used when 181.Va icmplim_output 182is non-zero. 183Defaults to 200. 184.It Va icmplim_output 185.Pq Vt boolean 186Enable/disable bandwidth limiting of ICMP replies. 187Defaults to true. 188.It Va drop_redirect 189.Pq Vt boolean 190Enable/disable dropping of ICMP Redirect packets. 191Defaults to false. 192.It Va log_redirect 193.Pq Vt boolean 194Enable/disable logging of ICMP Redirect packets. 195Defaults to false. 196.It Va bmcastecho 197.Pq Vt boolean 198Enable/disable ICMP replies received via broadcast or multicast. 199Defaults to false. 200.It Va reply_src 201.Pq Vt str 202An interface name used for the ICMP reply source in response to packets 203which are not directly addressed to us. 204By default continue with normal source selection. 205.It Va reply_from_interface 206.Pq Vt boolean 207Use the IP address of the interface the packet came through in for 208responses to packets which are not directly addressed to us. 209If enabled, this rule is processed before all others. 210By default, continue with normal source selection. 211Enabling this option is particularly useful on routers because it 212makes external traceroutes show the actual path a packet has taken 213instead of the possibly different return path. 214.It Va quotelen 215.Pq Vt integer 216Number of bytes from original packet to quote in ICMP reply. 217This number is internally enforced to be at least 8 bytes (per RFC792) 218and at most the maximal space left in the ICMP reply mbuf. 219.It Va tstamprepl 220.Pq Vt boolean 221Enable/disable replies to ICMP Timestamp packets. 222Defaults to true. 223.El 224.Sh ERRORS 225A socket operation may fail with one of the following errors returned: 226.Bl -tag -width Er 227.It Bq Er EISCONN 228when trying to establish a connection on a socket which 229already has one, or when trying to send a datagram with the destination 230address specified and the socket is already connected; 231.It Bq Er ENOTCONN 232when trying to send a datagram, but 233no destination address is specified, and the socket has not been 234connected; 235.It Bq Er ENOBUFS 236when the system runs out of memory for 237an internal data structure; 238.It Bq Er EADDRNOTAVAIL 239when an attempt is made to create a 240socket with a network address for which no network interface 241exists. 242.El 243.Sh SEE ALSO 244.Xr recv 2 , 245.Xr send 2 , 246.Xr inet 4 , 247.Xr intro 4 , 248.Xr ip 4 , 249.Xr pf.conf 5 250.Sh HISTORY 251The 252.Nm 253protocol appeared in 254.Bx 4.3 . 255