Routers connect networks at OSI layer 3. Routers interpret packet contents according to specified protocol sets, serving to connect networks with the same protocols (DECnet to DECnet, TCP/IP (Transmission Control Protocol/Internet Protocol) to TCP/IP). Routers are protocol-dependent; therefore, one router is needed for each protocol used by the network.

Routers are also responsible for the determination of the best path for data packets by routing them around failed segments of the network.