Implementing Cisco Networking Solutions

Address Resolution Protocol (ARP)

When a datagram is handed by the layer 3 of the host to the layer 2 of the host, it needs to be encapsulated with the layer 2 headers before it can be transmitted on the physical medium. Recall that an IP datagram at layer 3 has no knowledge of the layer 2 or the MAC address, and layer 2 encapsulation needs the source and the destination MAC addresses for creating the layer 2 headers and trailers. The discovery of the destination MAC address from the destination IP address is done using the ARP.

ARP is a query-response protocol. When the layer 2 host receives the IP datagram, it checks its ARP table to see if it has a MAC entry corresponding to the destination MAC address. If not, the host initiates an ARP ...