From: arunsy <[email-masked]>
Date: Wed, 20 Aug 2003 09:10:00 -0000

Hi all,
Would someone be able to explain the following clause in RFC 2328
section 16.5 (Incremental Updates -- Summary LSAs) Case 2 (Area A
is a transit area and the router is an ABR).

Case 2: Area A is a transit area and the router is an area
            border router.
            In this case, the following calculations must be
performed.
            First, if N's routing table entry presently contains one
or
            more inter-area paths that utilize the transit area Area
A,
            these paths should be removed. If this removes all paths
            from the routing table entry, the entry should be
            invalidated.  The entry's old values should be saved for
            later comparisons. Next the calculation in Section 16.3
must
            be run again for the single destination N. If the results
of
            this calculation have caused the cost to N to increase,
the
            complete routing table calculation must be rerun starting
            with the Dijkstra algorithm specified in Section 16.1.
            Otherwise, if the cost/path to an AS boundary router (as
            would be the case for a Type 4 summary-LSA) or to any
            forwarding addresses has changed, all AS-external-LSAs
will
             have to be reexamined by rerunning the calculation
in
            Section 16.4.  Otherwise, if N is now newly unreachable,
the
            calculation in Section 16.4 must be rerun for the single
            destination N, in case an alternate external route to N
            exists.

Why complete routing table calculation need to be rerun  if the
calculated new route has the higher cost than that of older one.
And how this behaviour is different from case 1?

And one more thing, how a router (ABR) knows whether the path of
the route is utilizing the transit area, since all the inter-area
routes in ABR are always associated with the Back Bone (even after
step 16.3).

Thanks and Regards,
ARun SY.