Configuring OSPF and OSPFv3 945What Are OSPF Routers and LSAs?When a PowerConnect switch is configured to use OSPF for dynamicrouting, it is considered to be an OSPF router. OSPF routers keep track of thestate of the various links they send data to. Routers exchange OSPF link stateadvertisements (LSAs) with other routers. External LSAs provide informationon static routes or routes learned from other routing protocols.OSPF defines various router types:• Backbone routers have an interface in Area 0.• Area border routers (ABRs) have interfaces in multiple areas.• Internal routers have all their interfaces in a single OSPF area.• Autonomous system boundary routers (ASBRs) redistribute routes fromother protocols and originate external LSAs.How Are Routes Selected?OSPF determines the best route using the route metric and the type of theOSPF route. The following order is used for choosing a route if more than onetype of route exists:1 Intra-area (the destination prefix is in the same area as the routercomputing the route)2 Inter-area (the destination is not in the same area as the router computingthe route3 External Type 14 External Type 2How Are OSPF and OSPFv3 Different?OSPFv3 is the Open Shortest Path First routing protocol for IPv6. It is similarto OSPFv2 in its concept of a link state database, intra/inter area, and ASexternal routes and virtual links. It differs from its IPv4 counterpart in anumber of respects. Peering is done through link-local addresses, and theprotocol is link rather than network centric; and addressing semantics havebeen moved to leaf LSAs.
