Wednesday, November 19, 2008

OSPF routing part VII - NSSA special case

Consider the following scenario whereby an NSSA area exists between router 2 and 7. As expected type 7 LSAs are allowed to flow from router 7 to router 2, into area 0. An additional requirement was imposed that router 7 must ONLY see a default route from router 2. This can be achieved by specifying a 'not so stubby totally stubby area'!

The issue with acheiving the lab requirements is that by default type 7 LSAs are allowed to flow in BOTH directions: i.e. router 2 <->router 7. To prevent the flow of type 7 LSAs from Router 2 the 'no-redistribution' option can be used

router 2
router ospf 1
area 27 nssa no-summary no-redistribution

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