Subject: Re: Question about NSSA

From: "Pat Murphy - (650)329-4044" <[email-masked]>
Date: Thu, 12 Sep 2002 12:21:25 -0700

Mani,

This depends on the implementation. Anytime you change the OSPF area
type and don't reset, strange things might happen. Since changing the
area type from Standard to NSSA forces every one of the area's
adjacencies to reset, there is some hope the old standard area's type
4 summary LSAs and its type 5 external LSAs will be flushed. If just
the type 4 LSAs are flushed, the original Type 5 LSA should no longer
compute a forwarding path.

Note that by default cisco's implementation requires that
redistribution into the NSSA must be specifically disabled. I can't
speak for other implementations. In this case if you don't
specifically disabled redistribution into the NSSA when you change
the area type to NSSA, then a new Type 5 advertisement will be
generated by the NSSA translator, presumably R3, with perhaps the
same forwarding address. This Type 5 LSA should install.

Pat

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From: Mani Devarajan <[email-masked]>
Date: Thu, 12 Sep 2002 13:34:15 -0700

Hi Pat,
 Thanks for the explanation.

 But still my doubt is not fully cleared.
 This is what I understood from your explanation,
 correct me if i am wrong.

 On changing Area2 to NSSA,

 1 - if redistribution is not disabled, then R3 will
     translate the type7 to type5 LSA and inject it in to
     backbone. So that connectivity is not broken in between
     R1 and R5.

 2 - if redistribution is disabled, R4 will flush the
     type 4 and type5 LSA which it generated previously.
     So that R1 will not be able to reach the external
     network.

Thanks,
Mani