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       This program is obsolete.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  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], --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 hostname separated by white-
	      space. 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, <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)