ARP(8)			   Linux Programmers 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  kernels 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
	      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.

       -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 ifas 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 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. 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 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,  with a lot of improve
       ments	from	net-tools    Maintainer    Bernd    Eckenfels	 .



net-tools			  2005-05-16				ARP(8)