ARP Protocol

To Translate the IP address to MAC address
Host A wants to send data to Host B which connected through the LAN

-Host A will check the corresponding between the destination IP address and MAC address in the lookup table (APR Cache)

-If this table is not in the cache memory of Host A, it will generate the ARP request through the broadcast Ethernet frame (destination MAC address is ff.ff.ff.ff.ff.ff) in order to know what is the corresponding MAC address

-Any host on the LAN will decode the Ethernet frame since that's the broadcast frame.The host which owns the IP address being broadcast by Host A will response back with the corresponding MAC address.

-This MAC address of destination Host will be updated in the Cache memory of Host A.

-Time to Life (TTL) for ARP entries need to be configured (some seconds in PC) to prevent Host A from sending the data to Host B where the Ethernet board already be replaced (hence, MAC address will be changed accordingly).

Note: ARP is using the broadcast frame in local network but not in different network(with router),.