Network2/Concept/Router

Routers are network nodes which forward encapsulated payload messages by receiving link-layer messages containing encapsulated payloads over one link and by decapsulating, inspecting, and potentially re-encapsulating the received payload for retransmission along a (usually) different link in the hopes of bringing the encapsulated payload closer to its destination. Routers permit the creation of internetworks from simpler networks.

The route along which a message is sent as it travels from its source to a destination is called a path. A message which is sent to one or more destinations along one or more routes is said to have been routed along a multipath.

Ultimately, routers just let us recapitulate earlier definitions "one layer up". Thus, (k+1)-nodes are k-networks, (k+1)-media are k-links, (k+1)-interfaces are k-routers, (k+1)-bridges are also k-routers (and the peering and transit agreements and links between them), and (k+1)-routers are called network address translators (NATs).