Subject: Unresolved virtual next hops

From: Igor Miroshnik <[email-masked]>
Date: Tue, 4 Mar 2003 16:26:08 -0500

All,

Section 16.3 of RFC2328 says:

"The calculation also determines the actual next hop(s) for those
destinations whose next hop was calculated as a virtual link in Sections
16.1 and 16.2. After completion of the calculation below, any paths
calculated in Sections 16.1 and 16.2 that still have unresolved virtual
next hops should be discarded."

As far as I understand, at list one next hop (may be suboptimal though) has
been already found during the intra-area routes calculation in the
corresponding Transit Area. Otherwise, we would not have advertised that
virtual link in our backbone Router LSA.

Can anybody give an example when there still remain unresolved virtual next
hops at the stage described above in 16.3?

Thanks,
Igor

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From: Acee Lindem <[email-masked]>
Date: Thu, 6 Mar 2003 10:08:38 -0500

> virtual link in our backbone Router LSA.

Hi Igor,

Section 16.1.1 says that virtual nexthop resolution should be deferred
until after section 16.3. However, I believe most implementations will
use the virtual next hop and only update it if there is a better path
through the transit area.

> hops at the stage described above in 16.3?

I guess this could happen if you ran your backbone intra-area SPF calculation
prior to the transit area calculation. In our implementation, we always run
the backbone intra-area SPF after all the other areas.

Good Luck,
Acee

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Acee