Difference between revisions of "ARP"
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Revision as of 02:49, 25 April 2012
Address Resolution Protocol (ARP) is used to resolve a network layer address to a link layer address, typically resolving a MAC address to an IPv4 address. For example, ARP may resolve the MAC address 01:23:45:67:89:AB to the IPv4 address 192.168.1.1.
How ARP Works
To resolve a MAC address to an IP address, ARP uses cached ARP tables containing IP address/MAC address pairs stored locally. For example, lets say Network Device A (NDA) wants to send a packet to Network Device B (NDB) with a MAC address of DE:AD:BE:EF:CA:FE and an IP address of 192.168.1.1, it first needs to resolve DE:AD:BE:EF:CA:FE into 192.168.1.1. To do this, it will first try and lookup the IP address 192.168.1.1 in its ARP table. If it finds the corresponding MAC address it will send the packet to the address it found, and it will (hopefully) reach its target. If it cannot find the corresponding MAC address it will send a broadcast ARP message (with a destination of FF:FF:FF:FF:FF:FF) requesting the IP address 192.168.1.1. NDB will now respond to that message with its MAC address (DE:AD:BE:EF:CA:FE), and will also store the MAC address of NDA in its own ARP cache table. NDA now has the MAC of NDB and can send its message along.
See Also
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ARP Visit the Protocols Portal for complete coverage.
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