ARP(8) manual page
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arp - manipulate the system ARP cache
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]
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.
- -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 displayed.
- -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 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.
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
published entries have the P flag.
/proc/net/arp,
/etc/networks
/etc/hosts
/etc/ethers
rarp(8)
, route(8)
, ifconfig(8)
, netstat(8)
Fred
N. van Kempen, <waltje@uwalt.nl.mugnet.org> with a lot of improvements from net-tools
Maintainer Bernd Eckenfels <net-tools@lina.inka.de>.
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