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.\" @(#)arp.8 8.1 (Berkeley) 6/6/93 29.\" $FreeBSD$ 30.\" 31.Dd July 13, 2020 32.Dt ARP 8 33.Os 34.Sh NAME 35.Nm arp 36.Nd address resolution display and control 37.Sh SYNOPSIS 38.Nm 39.Op Fl -libxo Ar options 40.Op Fl n 41.Op Fl i Ar interface 42.Ar hostname 43.Nm 44.Op Fl -libxo Ar options 45.Op Fl n 46.Op Fl i Ar interface 47.Fl a 48.Nm 49.Fl d Ar hostname 50.Op Cm pub 51.Nm 52.Fl d 53.Op Fl i Ar interface 54.Fl a 55.Nm 56.Fl s Ar hostname ether_addr 57.Op Cm temp 58.Op Cm blackhole No \&| Cm reject 59.Op Cm pub 60.Nm 61.Fl S Ar hostname ether_addr 62.Op Cm temp 63.Op Cm blackhole No \&| Cm reject 64.Op Cm pub 65.Nm 66.Fl f Ar filename 67.Sh DESCRIPTION 68The 69.Nm 70utility displays and modifies the Internet-to-Ethernet address translation 71tables used by the address resolution protocol 72.Pq Xr arp 4 . 73With no flags, the program displays the current 74.Tn ARP 75entry for 76.Ar hostname . 77The host may be specified by name or by number, 78using Internet dot notation. 79.Pp 80Available options: 81.Bl -tag -width indent 82.It Fl -libxo 83Generate output via 84.Xr libxo 3 85in a selection of different human and machine readable formats. 86See 87.Xr xo_parse_args 3 88for details on command line arguments. 89.It Fl a 90The program displays or, if it is used with the 91.Fl d 92flag, deletes all of the current 93.Tn ARP 94entries. 95.It Fl d 96A super-user may delete an entry for the host called 97.Ar hostname 98with the 99.Fl d 100flag. 101If the 102.Cm pub 103keyword is specified, only the 104.Dq published 105.Tn ARP 106entry 107for this host will be deleted. 108.Pp 109Alternatively, the 110.Fl d 111flag may be combined with the 112.Fl a 113flag to delete all entries. 114.It Fl i Ar interface 115Limit the operation scope to the 116.Tn ARP 117entries on 118.Ar interface . 119Applicable only to the following operations: 120display one, display all, delete all. 121.It Fl n 122Show network addresses as numbers (normally 123.Nm 124attempts to display addresses symbolically). 125.It Fl s Ar hostname ether_addr 126Create an 127.Tn ARP 128entry for the host called 129.Ar hostname 130with the Ethernet address 131.Ar ether_addr . 132The Ethernet address is given as six hex bytes separated by colons. 133The entry will be permanent unless the word 134.Cm temp 135is given in the command. 136If the word 137.Cm pub 138is given, the entry will be 139.Dq published ; 140i.e., this system will 141act as an 142.Tn ARP 143server, 144responding to requests for 145.Ar hostname 146even though the host address is not its own. 147In this case the 148.Ar ether_addr 149can be given as 150.Cm auto 151in which case the interfaces on this host will be examined, 152and if one of them is found to occupy the same subnet, its 153Ethernet address will be used. 154.Pp 155If the 156.Cm reject 157keyword is specified the entry will be marked so that traffic to 158the host will be discarded and the sender will be notified the 159host is unreachable. 160The 161.Cm blackhole 162keyword is similar in that traffic is discarded but the sender is 163not notified. 164These can be used to block external traffic to a host without 165using a firewall. 166.It Fl S Ar hostname ether_addr 167Is just like 168.Fl s 169except any existing 170.Tn ARP 171entry for this host will be deleted first. 172.It Fl f Ar filename 173Cause the file 174.Ar filename 175to be read and multiple entries to be set in the 176.Tn ARP 177tables. 178Entries 179in the file should be of the form 180.Pp 181.Bd -ragged -offset indent -compact 182.Ar hostname ether_addr 183.Op Cm temp 184.Op Cm blackhole No \&| Cm reject 185.Op Cm pub 186.Ed 187.Pp 188with argument meanings as given above. 189Leading whitespace and empty lines are ignored. 190A 191.Ql # 192character will mark the rest of the line as a comment. 193.El 194.Sh SEE ALSO 195.Xr inet 3 , 196.Xr libxo 3 , 197.Xr xo_parse_args 3 , 198.Xr arp 4 , 199.Xr ifconfig 8 , 200.Xr ndp 8 201.Sh HISTORY 202The 203.Nm 204utility appeared in 205.Bx 4.3 . 206