1.\" Copyright (c) 1985, 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. 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.Dd July 13, 2020 29.Dt ARP 8 30.Os 31.Sh NAME 32.Nm arp 33.Nd address resolution display and control 34.Sh SYNOPSIS 35.Nm 36.Op Fl -libxo Ar options 37.Op Fl n 38.Op Fl i Ar interface 39.Ar hostname 40.Nm 41.Op Fl -libxo Ar options 42.Op Fl n 43.Op Fl i Ar interface 44.Fl a 45.Nm 46.Fl d Ar hostname 47.Nm 48.Fl d 49.Op Fl i Ar interface 50.Fl a 51.Nm 52.Fl s Ar hostname ether_addr 53.Op Cm temp 54.Op Cm blackhole No \&| Cm reject 55.Op Cm pub 56.Nm 57.Fl S Ar hostname ether_addr 58.Op Cm temp 59.Op Cm blackhole No \&| Cm reject 60.Op Cm pub 61.Nm 62.Fl f Ar filename 63.Sh DESCRIPTION 64The 65.Nm 66utility displays and modifies the Internet-to-Ethernet address translation 67tables used by the address resolution protocol 68.Pq Xr arp 4 . 69With no flags, the program displays the current 70.Tn ARP 71entry for 72.Ar hostname . 73The host may be specified by name or by number, 74using Internet dot notation. 75.Pp 76Available options: 77.Bl -tag -width indent 78.It Fl -libxo 79Generate output via 80.Xr libxo 3 81in a selection of different human and machine readable formats. 82See 83.Xr xo_parse_args 3 84for details on command line arguments. 85.It Fl a 86The program displays or, if it is used with the 87.Fl d 88flag, deletes all of the current 89.Tn ARP 90entries. 91.It Fl d 92A super-user may delete an entry for the host called 93.Ar hostname 94with the 95.Fl d 96flag. 97.Pp 98The 99.Fl d 100flag may be combined with the 101.Fl a 102flag to delete all entries. 103.It Fl i Ar interface 104Limit the operation scope to the 105.Tn ARP 106entries on 107.Ar interface . 108Applicable only to the following operations: 109display one, display all, delete all. 110.It Fl n 111Show network addresses as numbers (normally 112.Nm 113attempts to display addresses symbolically). 114.It Fl s Ar hostname ether_addr 115Create an 116.Tn ARP 117entry for the host called 118.Ar hostname 119with the Ethernet address 120.Ar ether_addr . 121The Ethernet address is given as six hex bytes separated by colons. 122The entry will be permanent unless the word 123.Cm temp 124is given in the command. 125If the word 126.Cm pub 127is given, the entry will be 128.Dq published ; 129i.e., this system will 130act as an 131.Tn ARP 132server, 133responding to requests for 134.Ar hostname 135even though the host address is not its own. 136In this case the 137.Ar ether_addr 138can be given as 139.Cm auto 140in which case the interfaces on this host will be examined, 141and if one of them is found to occupy the same subnet, its 142Ethernet address will be used. 143.Pp 144If the 145.Cm reject 146keyword is specified the entry will be marked so that traffic to 147the host will be discarded and the sender will be notified the 148host is unreachable. 149The 150.Cm blackhole 151keyword is similar in that traffic is discarded but the sender is 152not notified. 153These can be used to block external traffic to a host without 154using a firewall. 155.It Fl S Ar hostname ether_addr 156Is just like 157.Fl s 158except any existing 159.Tn ARP 160entry for this host will be deleted first. 161.It Fl f Ar filename 162Cause the file 163.Ar filename 164to be read and multiple entries to be set in the 165.Tn ARP 166tables. 167Entries 168in the file should be of the form 169.Pp 170.Bd -ragged -offset indent -compact 171.Ar hostname ether_addr 172.Op Cm temp 173.Op Cm blackhole No \&| Cm reject 174.Op Cm pub 175.Ed 176.Pp 177with argument meanings as given above. 178Leading whitespace and empty lines are ignored. 179A 180.Ql # 181character will mark the rest of the line as a comment. 182.El 183.Sh SEE ALSO 184.Xr inet 3 , 185.Xr libxo 3 , 186.Xr xo_parse_args 3 , 187.Xr arp 4 , 188.Xr ifconfig 8 , 189.Xr ndp 8 190.Sh HISTORY 191The 192.Nm 193utility appeared in 194.Bx 4.3 . 195