OSPF Area Attribute Configuration 311■ The ID of an OSPF process is unique.■ One segment can belong to only one area and you must specify each OSPFinterface to belong to a particular area.OSPF Area AttributeConfigurationArea partition in OSPF reduces the number of LSAs in the network and enhancesOSPF scalability. To further reduce routing table size and the number of LSAs insome non-backbone areas on the edge of the AS, you can configure these areas asstub areas.A stub area cannot import any external route. For this reason the concept of NSSAarea is introduced. Type7 LSAs can be advertised in an NSSA area. Type7 LSAs aregenerated by ASBRs of the NSSA area, and will be transformed into AS-externalLSAs whey reaching ABRs in the NSSA area, which will then be advertised to otherareas.After area partition, the OSPF route updates between non-backbone areas areexchanged by way of the backbone area. Therefore, OSPF requires that all thenon-backbone areas should keep connectivity with the backbone area and thebackbone area must keep connectivity in itself.If the physical connectivity cannot be ensured due to various restrictions, you canconfigure OSPF virtual links to satisfy this requirement.ConfigurationPrerequisitesBefore configuring OSPF area attributes, perform the following tasks:■ Configuring the network layer addresses of interfaces so that the adjacentnodes are reachable to each other at the network layer■ Performing basic OSPF configurationConfiguring OSPF AreaAttributes Table 232 Configure OSPF area attributesOperation Command DescriptionEnter system view system-view -Enter OSPF view ospf [ process-id[ router-id router-id ] ]-Enter OSPF area view area area-id -Configure the current area to be astub areastub [ no-summary ] OptionalBy default, no area isconfigured as a stub area.Configure an area to be an NSSAareanssa[ default-route-advertise | no-import-route |no-summary ]*OptionalBy default, no area isconfigured as an NSSAarea.Configure the cost of the defaultroute transmitted by OSPF to a stubor NSSA areadefault-cost cost OptionalThis can be configured onan ABR only. By default,the cost of the defaultroute to a stub or NSSAarea is 1.
