Intraarea

Intraarea is a term used in computer networking to describe routing information and routes that are contained within a single routing area of a network protocol, most commonly Open Shortest Path First (OSPF) or Intermediate System to Intermediate System (IS-IS). The concept is used to distinguish routes that stay entirely inside one area from those that cross area boundaries. The term is sometimes written as intra-area or intraarea, depending on the source.

In the context of OSPF, an intra-area route is a destination reachable entirely within the same OSPF area as the router. Such routes are learned through intra-area link-state advertisements, including Router-LSAs and Network-LSAs, and are calculated by the area’s shortest-path first (SPF) algorithm. Intra-area routes do not require traversal of area border routers (ABRs). By contrast, inter-area routes are advertised between areas via ABRs using summary LSAs, allowing destinations in other areas to be reached through the backbone or other connected areas. External routes, redistributed from other routing protocols, may also appear as inter-area or external beyond the local area.

In IS-IS, intraarea routes correspond to Level-1 routes that remain within a single IS-IS area. Level-2 routes carry routing information between areas through the IS-IS backbone. This separation of levels helps IS-IS scale across large networks.

Understanding intraarea routing helps network designers and operators optimize convergence, manage routing table size within an area, and troubleshoot topology changes without unnecessary cross-area consideration. See also: OSPF, IS-IS, routing area, ABR, LSA, Level-1 and Level-2.