arp(8) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | MODES | OPTIONS | EXAMPLES | FILES | SEE ALSO | AUTHORS | COLOPHON

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 Address.

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 flag.

EXAMPLES         top

       /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.

FILES         top

       /proc/net/arp
       /etc/networks
       /etc/hosts
       /etc/ethers

SEE ALSO         top

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

AUTHORS         top

       Fred N. van Kempen <waltje@uwalt.nl.mugnet.org>, Bernd Eckenfels
       <net-tools@lina.inka.de>.

COLOPHON         top

       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 2020-12-18.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2018-11-03.)  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: proc(5)ifconfig(8)rarp(8)route(8)