arp



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]



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  sym-
              bolic 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], --display [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  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.


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 improve-
       ments    from    net-tools    Maintainer    Bernd    Eckenfels    <net-
       tools@lina.inka.de>.



net-tools                         5 Jan 1999                            ARP(8)

Man(1) output converted with man2html