Thursday, March 17, 2011

Address Resolution Protocol (ARP) Overview

For two machines on a given network to communicate, they must know the other machine’s physical
(or MAC) addresses. By broadcasting Address Resolution Protocols (ARPs), a host can dynamically
discover the MAC-layer address corresponding to a particular IP network-layer address.
After receiving a MAC-layer address, IP devices create an ARP cache to store the recently acquired
IP-to-MAC address mapping, thus avoiding having to broadcast ARPS when they want to recontact
a device. If the device does not respond within a specified time frame, the cache entry is flushed.
In addition to the Reverse Address Resolution Protocol (RARP) is used to map MAC-layer addresses
to IP addresses. RARP, which is the logical inverse of ARP, might be used by diskless workstations
that do not know their IP addresses when they boot. RARP relies on the presence of a RARP server
with table entries of MAC-layer-to-IP address mappings.

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