Part-4: OSPF Not So Stubby Area Configuration
A not-so-stubby area (NSSA) is a type of stub area that can import autonomous system external routes and send them to other areas, but still cannot receive AS-external routes from other areas. (Ref: Wikipedia.com)
Configure the above topology from part-1 but create the loopbacks on R5 instead on R3 and advertise them as RIP route and then redistribute them into OSPF.
Objective:
NSSA is a stubby area but it pass through the type-5 LSA as type-7, when they cross the NSSA these Type7 LSA converted back to type5, e.g. in our topology Area-2 is configured as totally stub area and blocking the external RIP network to entering into OSPF as shown below:
Due to this Other routers cant access RIP routes therefore we configure the area-2 as NSSA so that area-2 remains totally stubby area but it will pass RIP routes to ABR (R4).
R5 totally Stubby area configuration commands:
R5(config)#router ospf 1
R5(config-router)#area 2 nssa
R4 totally Stubby area configuration commands:
R4(config)# router ospf 1
R4(config-router)# area 2 nssa no-summary
Verification:
Show ip route on R4, you would find the RIP routes with N2 label.
R5#Show ip ospf 1 database
RIP routes in R5 are appears as type-7.
R4#Show ip ospf 1 database
But when they reach at R4, then again they converted into type-5.
