.\"	$OpenBSD: arp.8,v 1.13 2003/06/02 23:36:52 millert Exp $
.\"	$NetBSD: arp.8,v 1.7 1995/03/01 11:50:59 chopps Exp $
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.\"	from: @(#)arp.8	8.1 (Berkeley) 6/6/93
.\"
.Dd July 14, 1999
.Dt ARP 8
.Os
.Sh NAME
.Nm arp
.Nd address resolution display and control
.Sh SYNOPSIS
.Nm arp
.Op Fl n
.Ar hostname
.Nm arp
.Op Fl n
.Fl a
.Nm arp
.Fl d Ar hostname
.Nm arp
.Fl d a
.Nm arp
.Fl s Ar hostname ether_addr
.Op Ar temp | permanent
.Op Ar pub
.Nm arp
.Fl f Ar filename
.Sh DESCRIPTION
The
.Nm
program displays and modifies the Internet-to-Ethernet address translation
tables used by the address resolution protocol
.Pq Xr arp 4 .
With no flags, the program displays the current
.Tn ARP
entry for
.Ar hostname .
The host may be specified by name or by number,
using Internet dot notation.
.Pp
Available options:
.Bl -tag -width Ds
.It Fl a
The program displays or deletes all of the current
.Tn ARP
entries.
.It Fl d
A superuser may delete an entry for the host called
.Ar hostname
with the
.Fl d
flag.
.Pp
Alternatively, the
.Fl d
flag may be combined with the
.Fl a
flag to delete all entries, with hostname lookups automatically
disabled.
.It Fl n
Show network addresses as numbers (normally
.Nm
attempts to display addresses symbolically).
.It Fl s Ar hostname ether_addr
Create an
.Tn ARP
entry for the host called
.Ar hostname
with the Ethernet address
.Ar ether_addr .
The Ethernet address is given as six hex bytes separated by
colons.
The entry will be static, i.e., not time out, unless the word
.Ar temp
is given in the command.
A static ARP entry can be overwritten by network traffic, unless the word
.Ar permanent
is given.
If the word
.Ar pub
is given, the entry will be
.Dq published ;
i.e., this system will
act as an
.Tn ARP
server,
responding to requests for
.Ar hostname
even though the host address is not its own.
This behavior has traditionally been called
.Em "proxy arp" .
.It Fl f
Causes the file
.Ar filename
to be read and multiple entries to be set in the
.Tn ARP
tables.
Entries in the file should be of the form
.Pp
.Bd -filled -offset indent -compact
.Ar hostname ether_addr
.Op Ar temp | permanent
.Op Ar pub
.Ed
.Pp
with argument meanings as given above.
.El
.Sh EXAMPLES
To view the current
.Nm
table:
.Pp
.Dl $ arp -a
.Pp
To create a
.Em permanent
.Nm entry
(One that cannot be overwritten by other network traffic):
.Pp
.Dl # arp -s 10.0.0.2 00:90:27:bb:cc:dd permanent
.Pp
To create
.Em proxy arp
entries on an interface, fxp0,
for the IP Addresses 204.1.2.3 and 204.1.2.4, do a:
.Pp
.Bd -unfilled -offset indent -compact
# arp -s 209.1.2.3 00:90:27:bb:cc:dd pub
# arp -s 209.1.2.4 00:90:27:bb:cc:dd pub
.Ed
.Pp
(where 00:90:27:bb:cc:dd is the MAC address of fxp0)
.Sh SEE ALSO
.Xr inet 3 ,
.Xr arp 4 ,
.Xr ifconfig 8
.Sh HISTORY
The
.Nm
command appeared in
.Bx 4.3 .