NAME

arp − Address Resolution Protocol

DESCRIPTION

ARP is a protocol used to dynamically map between DARPA Internet and Ethernet addresses on a local area network.  It is used by the Ethernet interface drivers and is not directly accessible by users. 

ARP caches Internet-Ethernet address mappings.  When an interface requests a mapping for an unknown address, ARP drops that message and broadcasts a message on the associated network requesting the address mapping.  If a response is provided, the new mapping is cached and used with any subsequent messages to that address.  Until a response is obtained, ARP discards any messages to the unknown address.  ARP itself is not Internet or Ethernet specific, but this implementation of it is. 

ARP watches passively for hosts impersonating the local host (i.e., a host which responds to an ARP mapping request for the local host’s address) and can periodically probe a network looking for impostors. 

DIAGNOSTICS

Duplicate IP address!! sent from ethernet address: %x %x %x %x %x %x. 

ARP has discovered another host on the local network which responds to mapping requests for its own Internet address. 

Version 2.3  —  July 04, 1985