NAME

arp − Address Resolution Protocol

SYNOPSIS

pseudo-device ether

DESCRIPTION

ARP is a protocol used to dynamically map between DARPA Internet and 10Mb/s Ethernet addresses on a local area network.  It is used by all the 10Mb/s Ethernet interface drivers and is not directly accessible to users. 

ARP caches Internet-Ethernet address mappings.  When an interface requests a mapping for an address not in the cache, ARP queues the message which requires the mapping and broadcasts a message on the associated network requesting the address mapping.  If a response is provided, the new mapping is cached and any pending messages are transmitted.  ARP itself is not Internet or Ethernet specific; this implementation, however, is.  ARP will queue at most one packet while waiting for a mapping request to be responded to; only the most recently “transmitted” packet is kept. 

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 will, optionally, 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. 

SEE ALSO

ec(4S), inet(4F)
An Ethernet Address Resolution Protocol, RFC826, Dave Plummer, MIT (Sun 800-1059-01)

BUGS

Ioctls should be provided to create and delete entries from the arp tables so that it would be possible to talk to hosts which do not support the protocol. 

Sun System Release 1.0  —  17 August 1983