arp(8) — Linux manual page


ARP(8)               Linux System Administrator's Manual              ARP(8)

NAME         top

       arp - manipulate the system ARP cache

SYNOPSIS         top

       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]

DESCRIPTION         top

       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

MODES         top

       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.

OPTIONS         top

       -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

EXAMPLES         top

       /usr/sbin/arp -i eth0 -Ds eth1 pub

       This will answer ARP requests for on eth0 with the MAC
       address for eth1.

       /usr/sbin/arp -i eth1 -d

       Delete the ARP table entry for on interface eth1. This will
       match published proxy ARP entries and permanent entries.

FILES         top


SEE ALSO         top

       rarp(8), route(8), ifconfig(8), netstat(8)

AUTHORS         top

       Fred N. van Kempen <>, Bernd Eckenfels

COLOPHON         top

       This page is part of the net-tools (networking utilities) project.
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net-tools                        2008-10-03                           ARP(8)

Pages that refer to this page: proc(5)procfs(5)ifconfig(8)rarp(8)route(8)