ARP
The ARP protocol takes a different approach from ES-IS to acquiring
neighbor information.
Instead of sending periodic hello packets, the ARP protocol
populates its cache on an "as needed" basis.
If an end system running ARP wants to send data packets
to another destination and that destination's address information
is not found in its local cache, the end system tries to
determine whether the destination is on the same LAN as itself.
If the destination is on the same LAN,
the end system broadcasts an ARP query packet onto the LAN
seeking the destination's address information.
The destination sends a response packet back to the original
end system with the requested information, and the original end system
updates its cache and transmits the data packets.
If the destination is on a different LAN,
the transmitting end system sends the data packets to a router
on the LAN and lets it forward the packets.
There are different implementations of ARP for end stations
to determine what routers are attached to the LAN.
In some cases, an end system might be manually configured with a
router address; in others, end systems listen for routing protocol
packets and then extract router information from them.
This protocol is defined in [Plummer 1982].
Copyright © 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.
