arp - manipulate the system ARP cache
arp [
-vn] [
-H type] [
-i if]
[
-ae] [
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 ifname [
netmask nm]
pub
arp [
-vnD] [
-H type] [
-i if]
-f
[
filename]
Arp manipulates or displays the kernel's IPv4 network neighbour cache. It
can add entries to the table, delete one or display the current content.
ARP stands for Address Resolution Protocol, which is used to find the
media access control address of a network neighbour for a given IPv4 Address.
arp with no mode specifier will print the current content of the table.
It is possible to limit the number of entries printed, by specifying an
hardware address type, interface name or host address.
arp -d address will delete a ARP table entry. Root or netadmin
privilege is required to do this. The entry is found by IP address. If a
hostname is given, it will be resolved before looking up the entry in the ARP
table.
arp -s address hw_addr is used to set up a new table entry. The
format of the
hw_addr parameter is dependent on the hardware 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
publish 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. To simplify setting up entries for one of your own network
interfaces, you can use the
arp -Ds address ifname form. In that
case the hardware address is taken from the interface with the specified name.
- -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,
-t 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
- Use alternate BSD style output format (with no fixed
columns).
- -e
- Use default Linux style output format (with fixed
columns).
- -D, --use-device
- Instead of a hw_addr, the given argument is the name of an
interface. arp will use the MAC address of that interface for the
table entry. This is usually the best option to set up a proxy ARP entry
to yourself.
-
-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. 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. Also the dontpub option which is
available for delete and set operations cannot be used with 2.4 and newer
kernels.
-
-f filename, --file
filename
- Similar to the -s option, only this time the address
info is taken from file filename. This can be used if ARP entries
for a lot of hosts have to be 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 published entries have the
P flag.
/usr/sbin/arp -i eth0 -Ds 10.0.0.2 eth1 pub
This will answer ARP requests for 10.0.0.2 on eth0 with the MAC address for
eth1.
/usr/sbin/arp -i eth1 -d 10.0.0.1
Delete the ARP table entry for 10.0.0.1 on interface eth1. This will match
published proxy ARP entries and permanent entries.
/proc/net/arp
/etc/networks
/etc/hosts
/etc/ethers
ethers(5),
rarp(8),
route(8),
ifconfig(8),
netstat(8)
Fred N. van Kempen <
[email protected]>, Bernd Eckenfels
<
[email protected]>.