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

NAME
       arp - manipulate the system ARP cache

SYNOPSIS
       arp [-vn] [-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

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, --umeric
              shows  numerical  addresses  instead  of  trying to
              determine symbolic host, port or user names.

       -H type, --hw-type 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 (arc-
              net) , PROnet (pronet) , AX.25 (ax25)  and  NET/ROM
              (netrom).

       -a [hostname], --display [hostname]
              Shows  the  entries of the specified hosts.  If the
              hostname parameter is not used, all entries will be
              displayed.

       -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.

       -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 ker-
              nels 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.

       -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.

              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.

       Each complete entry in the ARP cache will be  marked  with
       the  C  flag. Permanent entries are marked with M and pub-
       lished entries have the P flag.

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

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

AUTHORS
       Fred N. van Kempen,  <waltje@uwalt.nl.mugnet.org>  with  a
       lot of improvements from net-tools Maintainer Bernd Ecken-
       fels <net-tools@lina.inka.de>.

net-tools                   5 Jan 1999                          1