Saturday, August 28, 2010

BSCI - OSPF - NSSA Totally Stubby Area

As I was reviewing my posts on OSPF LSA packet types and the Area types they are used in, it struck me that I missed off the last of the 4 area types.

We have a Stub area, totally stubby area, a Not-So-Stubby-Area, and the last one is NSSA Totally Stubby Area.

A NSSA Totally Stubby Area works in a similar manner to a Totally Stubby Area (blocking External type5 LSAs, Interarea route type4 LSA's and Summary type 3 LSA's). A single default route replaces all of these.

To configure a NSSA Totally Stubby Area you do the following:
On the NSSA ABR (this is the router that now has links to external networks/ Autonomous Systems):
R5(config)#router ospf 1
R5(config-router)#area 6 nssa
!

On the ABR that links to Area 0 do:
R4(config)#router ospf 1
R4(config-router)#area 6 nssa no-summary
!

In this situation R4 will automatically generate an O*N2 default route therefore you are not required to enter 'default-information originate'

Note that this is a Cisco propriortary config.

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