Areas
OSPF allows parts of a network to be grouped together into areas.
The topology within an area is hidden from the rest of the AS. Hiding this information enables a significant reduction in LSA traffic and reduces the computations needed to maintain the LSDB. Routing within the area is determined only by the topology of the area.
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Internal router (IR)—An internal router has all of its interfaces within the same area.
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Area border router (ABR)—An ABR has interfaces in multiple areas. It is responsible for exchanging summary advertisements with other ABRs.
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Autonomous system border router (ASBR)—An ASBR acts as a gateway between OSPF and other routing protocols, or other autonomous systems.