Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

On TCP/IP networks, the ARP protocol is used to match up an IP (Internet Protocol) address with a MAC (Medium Access Control) address. An IP address is a high-level internetwork address that identifies a specific computer on a subnetwork of interconnected networks. A MAC address is the hardwired address of a NIC (network interface card). MAC addresses are only used to forward frames between computers attached to the same network. They cannot be used to send frames to computers on other networks that are interconnected by routers. IP addressing must be used to forward frames across router boundaries (assuming TCP/IP networks).