3Com 10014299 Perform the following configuration in Ospf view, Configure an Nssa Area of Ospf

Configuring OSPF 433

In the following group network, an AS operating the OSPF protocol includes three areas, area 1, area 2, and area 0. Area 0 is the backbone area. The other ASs operate RIP. Area 1 is defined as an NSSA area. After an RIP route advertises to the NSSA ASBR that generates a Type-7 LSA and propagates in Area 1. After the Type-7 LSA reaches the NSSA ABR, it is transformed into a Type-5 LSA that is advertised to Area 0 and Area 2. The RIP route is generated as a Type-5 LSA and propagated in the OSPF AS by the ASBR of Area 2. This Type-5 LSA will not reach Area 1 because Area 1 is an NSSA area. On this point, an NSSA area and a stub area are the same.

Figure 146 Schematic Diagram of an NSSA Area

RIP
	NSSA	Router	NSSA
	ABR
		area 1	ASBR
		NSSA
Router	area 0	Router	Router
area 2
	Router
			RIP

Perform the following configuration in OSPF view:

Table 499 Configure an NSSA Area of OSPF

Operation	Command
Configure an area as NSSA area	nssa	area area-id [
	default-route-advertise ] [
	no-import-route ] [ no-summary ]
Cancel the configured NSSA area	undo	nssa area area-id

By default, no area is configured as an NSSA area.

The default-route-advertiseattribute generates default a Type-7 LSA. A Type-7 LSA default route is generated on the ABR no matter whether there is a default route 0.0.0.0 in the routing table while applying this parameter. A Type-7 LSA default route is only generated on an ASBR when there is a default route 0.0.0.0 in the routing table.

The no-import-routeattribute is used on the ASBR, which allows the OSPF route that is imported using the import-routecommand, to not be advertised to the NSSA area. If the NSSA router is both ASBR and ABR, this parameter option is always selected.

Configuring Route Route summary provides that the routing information is processed in the ABR. Summarization within Only one route is sent to other areas for the network segment configured with

the OSPF Domain. summary. One area can be configured with multiple summary network segments so that OSPF can summarize multiple network segments. When the ABR sends routing information to other areas, Sum_net_Lsa (Type 3 LSA) is generated for each network segment. If there are some continuous network segments in the area, they can be summarized into one network segment with a range command. Then the ABR only sends one summery LSA and all other LSAs in the summary network segment range specified with this command are not sent separately,