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, --numeric
	      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 tech-
	      nologies 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 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 perma-
	      nent  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  improvements  from  net-tools  Maintainer  Bernd  Eckenfels   <net-
       tools@lina.inka.de>.

net-tools							    5 Jan 1999								    ARP(8)