Address Resolution Protocol (ARP)

The Address Resolution Protocol (ARP) maps IP addresses to the corresponding MAC addresses of network devices within a local network. Since data packets are delivered at the link layer based on MAC addresses rather than IP addresses, a device must determine the matching MAC address for a known IP address before communication can take place. To do this, it sends an ARP request as a broadcast across the local network, to which the target device responds with its MAC address. This mapping is then stored for a period of time in the requesting device's ARP cache to avoid repeated requests. ARP is a fundamental part of communication in Ethernet and Wi-Fi networks. Because the protocol was originally developed without security mechanisms, it is vulnerable to attacks such as ARP spoofing, in which false mappings are injected into the network.