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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]

       This program is obsolete. For replacement check ip neigh.

       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  net‐
       work 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 inter‐
       faces, you can use the arp -Ds address ifname form. In that case the hardware address is taken from the inter‐
       face 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
              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 spec‐
              ified 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 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.



       Fred N. van Kempen <[email protected]>, Bernd Eckenfels <[email protected]>.

net-tools                                             2008-10-03                                               ARP(8)