arp(5P) arp(5P)
NAME
arp - Address Resolution Protocol
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.
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