From Linux Man Pages
arp - manipulate the system ARP cache
SYNOPSIS
arp [-vn] [-H type] [-i if] -a [hostname]
arp [-v] [-i if] -d hostname [pub]
arp [-v] [-H type] [-i if] -s hostname hw_addr [temp]
arp [-v] [-H type] [-i if] -s hostname hw_addr [netmask nm] pub
arp [-v] [-H type] [-i if] -Ds hostname ifa [netmask nm] pub
arp [-vnD] [-H type] [-i if] -f [filename]
DESCRIPTION
Arp manipulates the kernel's ARP cache in various ways. The primary options are clearing an address mapping
entry and manually setting up one. For debugging purposes, the arp program also allows a complete dump of the
ARP cache.
OPTIONS
-v, --verbose
Tell the user what is going on by being verbose.
-n, --numeric
shows numerical addresses instead of trying to determine symbolic host, port or user names.
-H type, --hw-type type
When setting or reading the ARP cache, this optional parameter tells arp which class of entries it should
check for. The default value of this parameter is ether (i.e. hardware code 0x01 for IEEE 802.3 10Mbps
Ethernet). Other values might include network technologies such as ARCnet (arcnet) , PROnet (pronet) ,
AX.25 (ax25) and NET/ROM (netrom).
-a [hostname], --display [hostname]
Shows the entries of the specified hosts. If the hostname parameter is not used, all entries will be dis-
played.
-d hostname, --delete hostname
Remove any entry for the specified host. This can be used if the indicated host is brought down, for
example.
-D, --use-device
Use the interface ifa's hardware address.
-i If, --device If
Select an interface. When dumping the ARP cache only entries matching the specified interface will be
printed. When setting a permanent or temp ARP entry this interface will be associated with the entry; if
this option is not used, the kernel will guess based on the routing table. For pub entries the specified
interface is the interface on which ARP requests will be answered.
NOTE: This has to be different from the interface to which the IP datagrams will be routed.
-s hostname hw_addr, --set hostname
Manually create an ARP address mapping entry for host hostname with hardware address set to hw_addr class,
but for most classes one can assume that the usual presentation can be used. For the Ethernet class, this
is 6 bytes in hexadecimal, separated by colons. When adding proxy arp entries (that is those with the pub-
lish flag set a netmask may be specified to proxy arp for entire subnets. This is not good practice, but
is supported by older kernels because it can be useful. If the temp flag is not supplied entries will be
permanent stored into the ARP cache.
NOTE: As of kernel 2.2.0 it is no longer possible to set an ARP entry for an entire subnet. Linux instead
does automagic proxy arp when a route exists and it is forwarding. See arp(7) for details.
-f filename, --file filename
Similar to the -s option, only this time the address info is taken from file filename set up. The name of
the data file is very often /etc/ethers, but this is not official. If no filename is specified /etc/ethers
is used as default.
The format of the file is simple; it only contains ASCII text lines with a hostname, and a hardware
address separated by whitespace. Additionally the pub, temp and netmask flags can be used.
In all places where a hostname is expected, one can also enter an IP address in dotted-decimal notation.
As a special case for compatibility the order of the hostname and the hardware address can be exchanged.
Each complete entry in the ARP cache will be marked with the C flag. Permanent entries are marked with M and pub-
lished entries have the P flag.
FILES
/proc/net/arp,
/etc/networks
/etc/hosts
/etc/ethers
RELATED
rarp(8), route(8), ifconfig(8), netstat(8)
CATEGORY