What is NSSA area in OSPF and why it is used for ?

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Accepted Answer

NSSA area is a type of OSPF area that allows external routes to be injected into the OSPF domain.

NSSA stands for Not-So-Stubby-Area.
It is used when an area needs to import external routes but still wants to maintain some level of stubbiness.
NSSA area has an ABR (Area Border Router) that translates Type 7 LSAs (Link State Advertisements) into Type 5 LSAs.
Type 7 LSAs are generated by ASBR (Autonomous System Boundary Router) in the NSSA area.
NSSA area can be used in scenarios where a company has multiple sites and wants to import external routes from the Internet into the OSPF domain.
NSSA area is also used in scenarios where a company has a remote site that needs to import external routes but doesn't want to flood the entire OSPF domain with those routes.

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