IGP

networkingISP & telecom

Stands for: Interior Gateway Protocol

Interior Gateway Protocol - the class of routing protocols that run inside one autonomous system: OSPF, IS-IS, EIGRP, RIP.

An IGP's job is fast, complete knowledge of one organization's own topology: link-state protocols (OSPF, IS-IS) flood the map and let every router compute shortest paths; older distance-vector protocols (RIP) passed rumors of distance instead. IGPs optimize for quick convergence and internal metrics, and they deliberately do not carry the whole internet - that scale and policy problem belongs to the exterior side, BGP. In MPLS networks the IGP also carries the labels' underlying reachability, which is why IGP design remains a carrier craft.

An interior gateway protocol routes within a single administrative domain, which is what separates it from BGP and explains almost every design difference between them. Inside your own network you control every router, you want fast convergence when a link fails, and you can trust the information being flooded, so the protocol optimizes for speed and correctness rather than for policy and distrust.

The practical choice is narrower than the category suggests. Link-state protocols, OSPF and IS-IS, have each router build an identical map and compute paths independently, which converges quickly and scales through areas. Distance-vector descendants like EIGRP tell neighbours about destinations rather than topology. In practice most enterprises run OSPF, most large carriers run IS-IS, and the deciding factors are operational familiarity and tooling far more often than protocol capability.

The boundary is where the interesting failures live. An IGP carries your infrastructure routes and should stay small and stable; the moment external routes are redistributed into it wholesale, convergence time and CPU both suffer, and a flap somewhere else becomes your problem. Keeping the IGP for infrastructure and letting BGP carry everything else is the discipline that keeps large networks predictable.

Also known as: igp, interior gateway protocol, interior routing

← All glossary entries