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NAME | SYNOPSIS | DESCRIPTION | MODES | OPTIONS | EXAMPLES | FILES | SEE ALSO | AUTHORS | COLOPHON |
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ARP(8) Linux System Administrator's Manual ARP(8)
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 <waltje@uwalt.nl.mugnet.org>, Bernd Eckenfels
<net-tools@lina.inka.de>.
This page is part of the net-tools (networking utilities)
project. Information about the project can be found at
⟨http://net-tools.sourceforge.net/⟩. If you have a bug report for
this manual page, see ⟨http://net-tools.sourceforge.net/⟩. This
page was obtained from the project's upstream Git repository
⟨git://git.code.sf.net/p/net-tools/code⟩ on 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2023-06-29.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
net-tools 2008-10-03 ARP(8)
Pages that refer to this page: ethers(5), proc(5), ifconfig(8), rarp(8), route(8)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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