Interior Gateway Protocol

Key Points

• Operates inside a routing domain
• Supports internal path selection and convergence
• Used by routers to share network reachability
• Includes distance-vector and link-state families

Definition

An Interior Gateway Protocol is a routing protocol used to exchange reachability information within a single network domain. It helps routers choose internal paths and converge on a shared view of the topology.

Concept

Interior Gateway Protocol is a core networking term for protocols that operate inside one administrative routing domain. It exists to let routers share topology and reachability information so traffic can move efficiently within the domain. It is used in enterprise networks, service provider cores, campus networks, and other routed environments. IGP behavior underpins internal path selection and fast convergence after topology changes.

Explainer

Interior Gateway Protocol works by allowing routers to advertise internal network information, compute best paths, and adapt when topology changes. Constraints include convergence time, routing table size, metric design, and the administrative boundaries that separate internal routing from external inter-domain routing. Failure modes include route flapping, poor metric planning, slow convergence, loop formation under misconfiguration, and inconsistent topology views across routers. Tradeoffs involve speed versus scalability, simplicity versus control, and route optimality versus protocol overhead. Interior Gateway Protocol matters because it is a primary mechanism for internal network stability and traffic engineering. Cross-industry relevance is broad because any sizeable routed network relies on some form of interior routing protocol.