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List:       ms-ospf
Subject:    Re: NSSA Problem
From:       Amit Srivastava <ospfisfun () YAHOO ! COM>
Date:       2002-08-16 4:19:48
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Hi Pat and Acee,
    Thanks a lot for your help i really understood the
concept.
Regards
Amit


--- "Pat Murphy - (650)329-4044"
<pmurphy@NOC.USGS.NET> wrote:
> Amit,
>
> Sorry to be slow late with this posting. I have been
> unavailable lately due to USGS security concerns.
>
> Consider the following example. A0, B0, C0 are area
> 0
> routers. A0 and B0 are ABRs for NSSA 1, both of
> which
> translate Type 7 LSAs into Type 5 LSAs. D1 is an
> ASBR for
> NSSA 1 which learns an external route for N1 from
> E1, an
> EIGRP peer.
>
>                         C0
>                        .   .
>                      .       .
>             10Mbps .           . T1
>                  .    Area 0     .
>                .                   .
>              A0     - - - - -      B0
>                .                   .
>                  .    NSSA 1     .
>            128Kbps .           . T1
>             ISDN     .       .
>            backup     .   .
>                         D1
>                         .
>                         .
>                         .
>                         E1
>                         .
>                         .
>                         N1
>
> If D1 sets a 0.0.0.0 forwarding address for N1 in
> its type
> 7 LSA, A0 and B0 would have to do the same in the
> Type 5
> translation of this LSA. Thus C0 would see, via the
> Type 5
> LSA translation, the 10Mbps path through A0 as the
> shortest
> path to N1. If D1 sets a non-zero forwarding addess,
> C0
> correctly computes the shortest path to N1 as the T1
> link
> through B0.
>
> Note that even if both A0 and B0 originated a type 4
> summary link for D1, the same logic would still
> hold, as
> the type 5 LSA advertisement for N1 originates from
> A0 and
> B0, not D1.
>
> Pat


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