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Level 1
Level 1

Dear expert,


Need you suggestion to configure the NSSA area. What would be the best practice to configure NSSA? Can we make area0 as NSSA, if we can not make area 0 nssa can some on please help me to understand why? Thanks for you suggestions.

3 Replies 3

Rolf Fischer
Level 9
Level 9


area 0 is a Type-5 (external routing information) capable area by definition, a NSSA is not Type-5 capable.

So area 0 always has to be a non-stub/regular area in order to be able to flood Type-5 LSAs into other non-stub areas.

A NSSA reduces the size of the LSDB similar to what stub areas do (there is also a totally option), but in contrast to stub areas you can inject external routing information. For this purpose, a new type of external LSAs was introduced (7) which has a scope limited to the NSSA, but can be translated into AS-wide Type-5 LSAs by a NSSA Border Router.

Link: OSPF Not-So-Stubby Area (NSSA)




Got that.... thanks Folf.


So basically area 0 is a capable of Type 5 LSA, in my infra if ASBR is connected to the area0 so not need to configure the NSSA.


Thanks for you input.

Well, you can place an ASBR in every Type-5 capable area and in a NSSA as well. An ASBR can even be an ABR at the same time.

Unlike internal LSAs, Type-5 LSAs are flooded unchanged among all non-stub areas and their inter-area reachability is achieved by evaluating a special field (Forwarding Address) or, if not set, the Type-4 LSA for the advertising ASBR. Stub areas have to rely on their default-routes to reach external networks.

This concepts can be somewhat confusing, feel free to ask further.




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