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ARP(8)                     Linux Programmer's Manual                    ARP(8)



NAME
       arp - manipulate the system ARP cache


SYNOPSIS
       arp [-evn] [-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]


NOTE
       This program is obsolete. For replacement check ip neighbor.


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, --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 [hostname], --all [hostname]
              Shows the entries of the specified hosts.  If the hostname parameter is not used, all  entries  will  be
              displayed.  The entries will be displayed in alternate (BSD) style.

       -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.

       -e     Shows the entries in default (Linux) style.

       -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 hardware address and a host-
              name 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.


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


SEE ALSO
       ip(8)


AUTHORS
       Fred  N.  van  Kempen,  <waltjeATuwalt.org> with a lot of improvements from net-tools Maintainer Bernd
       Eckenfels <net-toolsATlina.de>.



net-tools                         5 Jan 1999                            ARP(8)