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arp(7P)								       arp(7P)

NAME
       arp - Address Resolution Protocol

DESCRIPTION
       ARP  is	a  protocol used to dynamically map between DARPA Internet and
       hardware station addresses.  It is used by all LAN drivers.

       ARP caches Internet-to-hardware	station	 address  mappings.   When  an
       interface  requests  a  mapping	for  an	 address not in the cache, ARP
       queues the message that requires the mapping, and broadcasts a  message
       on  the associated network requesting the address mapping if the encap‐
       sulation method has been enabled for the interface.  If a  response  is
       provided,  the  new mapping is cached and any pending message is trans‐
       mitted.	ARP queues at most one packet  while  waiting  for  a  mapping
       request	to  be	responded  to;	only the most recently ``transmitted''
       packet is kept.

       To facilitate communications with systems that do not  use  ARP,	 calls
       are  provided  to  enter and delete entries in the Internet-to-hardware
       station address tables.

   Application Usage:
       Each call takes the same structure as an argument.  sets an ARP	entry,
       gets  an	 ARP  entry,  and  deletes  an	ARP entry.  These calls can be
       applied to any socket descriptor s, but only by	the  super-user.   The
       structure contains:

       The  address  family  for  the must be for the it must be The only flag
       bits that can be written are and Fibre Channel hosts only  support  the
       flag.   causes  the entry to be permanent.  specifies that the ARP code
       should respond to ARP requests for the indicated host coming from other
       machines.   This	 allows	 a  host to act as an ARP server, which may be
       useful in convincing an ARP-only machine to talk to a non-ARP machine.

       ARP watches passively for hosts impersonating the local host  (i.e.,  a
       host  that  responds  to	 an  ARP  mapping request for the local host's
       address).

DIAGNOSTICS
       This message printed on the console screen means that
	    ARP has discovered another host on the local network that responds
	    to mapping requests for its own Internet address.

WARNINGS
       To enable the encapsulation method, use the command (see ifconfig(1M)).

AUTHOR
       ARP was developed by the University of California, Berkeley.

SEE ALSO
       ifconfig(1M), inet(3N), lan(7), arp(1M).

       RFC826, Dave Plummer, Network Information Center, SRI.

								       arp(7P)

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