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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.\" $FreeBSD$ 34.\" 35.Dd February 9, 2007 36.Dt ICMP 4 37.Os 38.Sh NAME 39.Nm icmp 40.Nd Internet Control Message Protocol 41.Sh SYNOPSIS 42.In sys/types.h 43.In sys/socket.h 44.In netinet/in.h 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 54through a 55.Dq raw socket 56for network monitoring 57and diagnostic functions. 58The 59.Fa proto 60parameter to the socket call to create an 61.Tn ICMP 62socket 63is obtained from 64.Xr getprotobyname 3 . 65.Tn ICMP 66sockets are connectionless, 67and are normally used with the 68.Xr sendto 2 69and 70.Xr recvfrom 2 71calls, though the 72.Xr connect 2 73call may also be used to fix the destination for future 74packets (in which case the 75.Xr read 2 76or 77.Xr recv 2 78and 79.Xr write 2 80or 81.Xr send 2 82system calls may be used). 83.Pp 84Outgoing packets automatically have an 85.Tn IP 86header prepended to 87them (based on the destination address). 88Incoming packets are received with the 89.Tn IP 90header and options intact. 91.Ss Types 92ICMP messages are classified according to the type and code fields 93present in the ICMP header. 94The abbreviations for the types and codes may be used in rules in 95.Xr pf.conf 5 . 96The following types are defined: 97.Bl -column x xxxxxxxxxxxx -offset indent 98.It Sy Num Ta Sy Abbrev. Ta Sy Description 99.It 0 Ta echorep Ta "Echo reply" 100.It 3 Ta unreach Ta "Destination unreachable" 101.It 4 Ta squench Ta "Packet loss, slow down" 102.It 5 Ta redir Ta "Shorter route exists" 103.It 6 Ta althost Ta "Alternate host address" 104.It 8 Ta echoreq Ta "Echo request" 105.It 9 Ta routeradv Ta "Router advertisement" 106.It 10 Ta routersol Ta "Router solicitation" 107.It 11 Ta timex Ta "Time exceeded" 108.It 12 Ta paramprob Ta "Invalid IP header" 109.It 13 Ta timereq Ta "Timestamp request" 110.It 14 Ta timerep Ta "Timestamp reply" 111.It 15 Ta inforeq Ta "Information request" 112.It 16 Ta inforep Ta "Information reply" 113.It 17 Ta maskreq Ta "Address mask request" 114.It 18 Ta maskrep Ta "Address mask reply" 115.It 30 Ta trace Ta Traceroute 116.It 31 Ta dataconv Ta "Data conversion problem" 117.It 32 Ta mobredir Ta "Mobile host redirection" 118.It 33 Ta ipv6-where Ta "IPv6 where-are-you" 119.It 34 Ta ipv6-here Ta "IPv6 i-am-here" 120.It 35 Ta mobregreq Ta "Mobile registration request" 121.It 36 Ta mobregrep Ta "Mobile registration reply" 122.It 39 Ta skip Ta SKIP 123.It 40 Ta photuris Ta Photuris 124.El 125.Pp 126The following codes are defined: 127.Bl -column x xxxxxxxxxxxx xxxxxxxx -offset indent 128.It Sy Num Ta Sy Abbrev. Ta Sy Type Ta Sy Description 129.It 0 Ta net-unr Ta unreach Ta "Network unreachable" 130.It 1 Ta host-unr Ta unreach Ta "Host unreachable" 131.It 2 Ta proto-unr Ta unreach Ta "Protocol unreachable" 132.It 3 Ta port-unr Ta unreach Ta "Port unreachable" 133.It 4 Ta needfrag Ta unreach Ta "Fragmentation needed but DF bit set" 134.It 5 Ta srcfail Ta unreach Ta "Source routing failed" 135.It 6 Ta net-unk Ta unreach Ta "Network unknown" 136.It 7 Ta host-unk Ta unreach Ta "Host unknown" 137.It 8 Ta isolate Ta unreach Ta "Host isolated" 138.It 9 Ta net-prohib Ta unreach Ta "Network administratively prohibited" 139.It 10 Ta host-prohib Ta unreach Ta "Host administratively prohibited" 140.It 11 Ta net-tos Ta unreach Ta "Invalid TOS for network" 141.It 12 Ta host-tos Ta unreach Ta "Invalid TOS for host" 142.It 13 Ta filter-prohib Ta unreach Ta "Prohibited access" 143.It 14 Ta host-preced Ta unreach Ta "Precedence violation" 144.It 15 Ta cutoff-preced Ta unreach Ta "Precedence cutoff" 145.It 0 Ta redir-net Ta redir Ta "Shorter route for network" 146.It 1 Ta redir-host Ta redir Ta "Shorter route for host" 147.It 2 Ta redir-tos-net Ta redir Ta "Shorter route for TOS and network" 148.It 3 Ta redir-tos-host Ta redir Ta "Shorter route for TOS and host" 149.It 0 Ta normal-adv Ta routeradv Ta "Normal advertisement" 150.It 16 Ta common-adv Ta routeradv Ta "Selective advertisement" 151.It 0 Ta transit Ta timex Ta "Time exceeded in transit" 152.It 1 Ta reassemb Ta timex Ta "Time exceeded in reassembly" 153.It 0 Ta badhead Ta paramprob Ta "Invalid option pointer" 154.It 1 Ta optmiss Ta paramprob Ta "Missing option" 155.It 2 Ta badlen Ta paramprob Ta "Invalid length" 156.It 1 Ta unknown-ind Ta photuris Ta "Unknown security index" 157.It 2 Ta auth-fail Ta photuris Ta "Authentication failed" 158.It 3 Ta decrypt-fail Ta photuris Ta "Decryption failed" 159.El 160.Ss MIB Variables 161The 162.Tn ICMP 163protocol implements a number of variables in the 164.Va net.inet.icmp 165branch of the 166.Xr sysctl 3 167MIB. 168.Bl -tag -width ".Va icmplim_output" 169.It Va maskrepl 170.Pq Vt boolean 171Enable/disable replies to ICMP Address Mask Request packets. 172Defaults to false. 173.It Va maskfake 174.Pq Vt "unsigned integer" 175When 176.Va maskrepl 177is set and this value is non-zero, 178it will be used instead of the real address mask when 179the system replies to an ICMP Address Mask Request packet. 180Defaults to 0. 181.It Va icmplim 182.Pq Vt integer 183Bandwidth limit for ICMP replies in packets/second. 184Used when 185.Va icmplim_output 186is non-zero. 187Defaults to 200. 188.It Va icmplim_output 189.Pq Vt boolean 190Enable/disable bandwidth limiting of ICMP replies. 191Defaults to true. 192.It Va drop_redirect 193.Pq Vt boolean 194Enable/disable dropping of ICMP Redirect packets. 195Defaults to false. 196.It Va log_redirect 197.Pq Vt boolean 198Enable/disable logging of ICMP Redirect packets. 199Defaults to false. 200.It Va bmcastecho 201.Pq Vt boolean 202Enable/disable ICMP replies received via broadcast or multicast. 203Defaults to false. 204.It Va reply_src 205.Pq Vt str 206An interface name used for the ICMP reply source in response to packets 207which are not directly addressed to us. 208By default continue with normal source selection. 209.It Va reply_from_interface 210.Pq Vt boolean 211Use the IP address of the interface the packet came through in for 212responses to packets which are not directly addressed to us. 213If enabled, this rule is processed before all others. 214By default, continue with normal source selection. 215Enabling this option is particularly useful on routers because it 216makes external traceroutes show the actual path a packet has taken 217instead of the possibly different return path. 218.It Va quotelen 219.Pq Vt integer 220Number of bytes from original packet to quote in ICMP reply. 221This number is internally enforced to be at least 8 bytes (per RFC792) 222and at most the maximal space left in the ICMP reply mbuf. 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