944 Configuring OSPF and OSPFv3OSPF OverviewOSPF is an Interior Gateway Protocol (IGP) that performs dynamic routingwithin a network. PowerConnect M6220, M6348, M8024, and M8024-kswitches support two dynamic routing protocols: OSPF and RoutingInformation Protocol (RIP).Unlike RIP, OSPF is a link-state protocol. Larger networks typically use theOSPF protocol instead of RIP.What Are OSPF Areas and Other OSPF Topology Features?The top level of the hierarchy of an OSPF network is known as an OSPFdomain. The domain can be divided into areas. Routers within an area mustshare detailed information on the topology of their area, but require lessdetailed information about the topology of other areas. Segregating a networkinto areas enables limiting the amount of route information communicatedthroughout the network.Areas are identified by a numeric ID in IP address format n.n.n.n (note,however, that these are not used as actual IP addresses). For simplicity, thearea can be configured and referred to in normal integer notation. Forexample, Area 20 is identified as 0.0.0.20 and Area 256 as 0.0.1.0. The areaidentified as 0.0.0.0 is referred to as Area 0 and is considered the OSPFbackbone. All other OSPF areas in the network must connect to Area 0directly or through a virtual link. The backbone area is responsible fordistributing routing information between non-backbone areas.A virtual link can be used to connect an area to Area 0 when a direct link isnot possible. A virtual link traverses an area between the remote area and Area0.A stub area is an area that does not accept external LSAs (LSAs generated byredistributing routes) that were learned from a protocol other than OSPF orwere statically configured. These routes typically send traffic outside the AS.Therefore, routes from a stub area to locations outside the AS use the defaultgateway. A virtual link cannot be configured across a stub area. A Not SoStubby Area can import limited external routes only from a connected ASBR.
