ARP(8) Linux Programmer's Manual ARP(8)
NAME
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, --umeric
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 (arc-
net) , 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.
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ARP(8) Linux Programmer's Manual ARP(8)
-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 Interface will be
printed. Setting a permanent or temp ARP entry will
be used on the specified device. If no device is
given, the kernels guess the device from the rout-
ing 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 witch the IP Packages 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. Proxy
arp for routing entire networks is not a good pro-
tocol, but its sometimes useful so supported. If
the temp flag is not supplied entries will be per-
manent stored into the ARP cache.
-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.
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.
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
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AUTHOR
Fred N. van Kempen, <waltje@uwalt.nl.mugnet.org> with a
lot of improvements from net-tools Maintainer Bernd Ecken-
fels <net-tools@lina.inka.de>.
net-tools 15 May 1996 3