ARP (Address Resolution Protocol) is used to convert the IP address to its corresponding Ethernet (MAC) address. When a packet comes to the Network layer (OSI), it has an IP address and a data link layer packet that needs the MAC address of the destination device. In this case, the sender uses the ARP protocol.
The ARP request
The ARP reply
A host machine might want to send a message to another machine in the same subnet. The host machine only knows the IP address while the MAC address is required to send the message at the data link layer. In this situation, the host machine broadcasts the ARP request. All machines in the subnet receive the message. The Ethernet protocol type of the value is 0x806.