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Friday, April 29, 2011

Totally NSSA Filters type 3, 4 and type 5 LSA’s.


NSSA totally stubby area
An addition to the standard functionality of an NSSA, the totally stubby NSSA is an NSSA that takes on the attributes of a TSA, meaning that type 3 and 4 summary routes are not flooded into this type of area. It is also possible to declare an area both totally stubby and not-so-stubby, which means that the area will receive only the default route from area 0.0.0.0, but can also contain an autonomous system boundary router (ASBR) that accepts external routing information and injects it into the local area, and from the local area into area 0.0.0.0.
Redistribution into an NSSA area creates a special type of LSA known as TYPE 7, which can exist only in an NSSA area. An NSSA ASBR generates this LSA, and an NSSA ABR router translates it into type 5 LSA which gets propagated into the OSPF domain.
https://learningnetwork.cisco.com/message/111497
 

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