3.6.d [iii] Internal router, ABR, ASBR
OSPF uses flooding to exchange link-state updates between routers. Any change in routing information is flooded to all routers in the network . Areas are introduced to put a boundary on the explosion of link-state updates. Flooding and calcwithin an area have the exact link-state database. Routers that belong to multiple areas, and connect these areas to the backbone area are called area border routers (ABR). ABRs must therefore maintain information describing the backbone areas and other attached areas.
An area is interface specific . A router that has all of its interfaces within the same area is called an internal router (IR). A router that has interfaces in multiple areas is called an area border router (ABR). Routers that act as gateways (redistribution) between OSPF and other routing protocols (IGRP, EIGRP, IS-IS, RIP, BGP, Static) or other instances of the OSPF routing process are called autonomous system boundary router (ASBR). Any router can be an ABR or an ASBR. The P-bit is used in order to tell the NSSA ABR whether to translate type 7 into type 5.
Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 3537-3544). . Kindle Edition. ulation of the Dijkstra algorithm on a router is limited to changes within an area. All routers