Address Resolution Protocol
 
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I understand the theory behind Address Resolution Protocol, but how does a remote machine differentiate between different media access control addresses of machines on the same subnet by sending out FFFF.FFFF.FFFF for the destination MAC? The sender wants a reply from the DNS box.
ARP works by broadcasting the request to every station under the convention that only the machine that "owns" the IP address being requested will answer the ARP request by sending the answer (including the correct MAC address) directly to the requesting station. ARP requests are broadcast to the whole segment. The requester fills in its own MAC and IP address in the sender address fields, and puts the known IP address of the target in the target IP address field. In addition, the requester puts all ones in the target MAC field (FFFF.FFF.FFFF is the Ethernet broadcast address). The replying machine (which is either the owner of the IP address being sought or the router that knows the way) replaces the broadcast address with the target's MAC address, swaps the sender and target pairs, and unicasts the answer directly back to the requesting machine.
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As a network architect at Change at Work in Houston, Blass understands the strain of developing and managing networks. Send your problems to dr.internet@changeatwork.com
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