Routing

Routing is the process of selecting paths for traffic in a network to move data from source to destination. Routers perform forwarding decisions using routing tables that map destination prefixes to next-hop interfaces. Routing aims for efficient, reliable delivery across networks of growing size.

Routing can be static or dynamic. Static routing uses manually configured routes; dynamic routing automatically discovers paths using protocols. Interior gateway protocols (IGP) such as RIP, OSPF, IS-IS are used within an organization; exterior gateway protocols (EGP) such as BGP manage routing between autonomous systems on the Internet.

Dynamic routing relies on routing algorithms and metrics. Distance-vector protocols share route information with neighbors; link-state protocols gather information about the network's topology and compute shortest paths using algorithms like Dijkstra. Metrics can include hop count, bandwidth, delay, reliability, and MTU. Routes are stored in a routing table with entries for destination prefixes, next hop, interface, metric, and protocol.

Convergence and stability are important concerns; improper configurations can cause routing loops or large convergence times. Techniques such as route poisoning, split horizon, hold-down timers, and route summarization mitigate problems. Security considerations include route hijacking and authentication of routing updates in many protocols.