Address Resolution Protocol (ARP)
TCP/IP addresses are 32 bits and represent a network, subnet, and host ID.
Addresses on LANs are represented by physical (MAC) layer addresses and they are 48 bits in length.
ARP provides the mapping between a host’s 32-bit IP address and its 48-bit MAC address.
ARP works only on the local subnet (it cannot traverse routers).
ARP builds a table of IP/MAC addresses to properly format a source and destination address field in a packet.