Re: NSSA forwarding address

[Vivek Dubey <[e-mail]>]

Hi Somnath,
RFC preference rule for picking Fwd addr

1) If the network between the NSSA AS boundary router and the
adjacent AS is
    advertised into OSPF as an internal OSPF route (choose next
hop)
2) Loop back interface
3) NSSA interface
4) Stub interface

 From what i understood from your mail :
if you choose loop back address problem
scenarion will not occur.

vivek

On Fri, 30 May 2003 somnath mani wrote :
>Folks,
>The RFC for NSSA states that we set the forwarding address in a
>type 7 LSA to be that of any interface on which OSPF is
>configured ( barring the scenario, when the interface to the
>other AS is internal to OSPF).
>This is a problem when you are trying to do equal cost multipath
>routing and in some other situations.
>
>Consider a router A with 2 interfaces configured to run OSPF, IF1
>and IF2. The cost on both these interfaces is 10 , let's say.
>
>If we pick the forwarding address to be IF2 ( We are
>redistributing at router A), then a router B adjacent to A over
>IF1 will compute the cost for a type 7 LSA route to be 10 + 10 =
>20 ( Assume either ends of the interfaces are configured with
>same cost). Whereas, router C, adjacent to router A over IF2 will
>compute the same to be 10 !!
>
>Routers upstream of Router B and C will prefer to route via C !
>
>Would it not be better if we set the forwarding address to be the
>router ID ( provided we have added it as a stub host ) ?
>
>Thanks
>Somnath
>
>
>
>
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