Black Box Explains... Router Basics.
Routers are intelligent, high-level devices that enable individual, unique, logical networks to communicate with each other while maintaining their own identities. A router forms the boundary between networks. It connects logically separate networks operating under the same transport protocol such as TCP/IP or SNA. Routers are protocol-dependent and must support the protocols being routed. Thanks to the Internet, these protocols have become fairly standardized.
Part of a routers function is to choose a path over which to send packets. This path may involve multiple hops from the source device to a destination that can be across multiple physical networkseven on another continent. In an enterprise-wide WAN divided by routers, each network is managed separately and is assigned a unique network number (OSI Layer 3), usually an IP address.
A router learns the network number of each connected LAN and stores these numbers in a routing table. If a network changes, the router learns and stores the change automatically. The router uses these routing tables combined with a routing algorithm to decide the best way to route a packet.