A TCP/IP network layer protocol responsible for resolving IP addresses into MAC addresses. Address Resolution Protocol (ARP) is defined in Request for Comments (RFC) number 826.
When a TCP/IP-aware application tries to access another TCP/IP host using its IP address, the destination host’s IP address must first be resolved into a MAC address so that the frame can be addressed and placed on the wire and then be recognized by the destination host's network interface card (NIC).
This is because network interface cards operate at the physical layer (layer 1) and data-link layer (layer 2) of the OSI model and must use physical addresses (such as MAC addresses) instead of logical addresses (such as IP addresses) for network communication.
ARP broadcasts an ARP Request packet that effectively says, «Who has the following IP address?» This broadcast requests the MAC address of the destination host. The destination host then responds with an ARP Reply packet containing its own MAC address.
The requesting host next temporarily stores the IP-to-MAC-address mapping in its local ARP cache in case this is required again within a short interval of time.
ARP acronym means Address Resolution Protocol and it is responsible for resolving IP addresses to MAC addresses.