ARP Request
If a source computer cannot locate an IP to MAC address mapping in its ARP table, it must obtain the correct mapping.
To obtain the correct mapping, the device initiates an ARP request to discover the destination’s MAC address.
A source computer broadcasts an ARP request to all hosts on the local segment to find the destination computer’s MAC address.
Each device passes the packet up to the Network layer of the OSI model because the MAC address is a broadcast and meant for every host.
Then, the computer looks to see if its IP address matches the IP address in the packet.