Hi,
 I need a clarification on routes to ASBR. We can have
multiple intra area routes & inter area route to ASBR.
When we add to the routing table, section 16.2 point 5
asks to check if the route is available in that area.
If it is not available in that area, we will add the
route. So the router type routing table will have
routes in more than one area.

It is best explained by the example below:

If suppose an ASBR is reachable through 2 ABRs (ABR1 &
ABR0 connected to areas Area 1 & Area 0).
                   10(cost)
               ASBR---------ABR1
               | |
      10(cost) | |10(cost)
               | |
              ABR0--------Normal Router
                  10(cost)

In the above diagram if ASBR, ABR1 & ABR0 are in Area
1
and Normal router,ABR0 & ABR1 area in Area 0.

ABR1 & ABR0 will have intra area route & inter area
route to ASBR.(so routes in Area 1 Area 0). If we
have routes in Area 1 & Area 0, we cannot have Type-4
LSA in Area 1 & Area 0. So the ASBR will become
unreachable from Normal router.

So if we were to only follow point 5 in section 16.2
in RFC 2328, Normal router will not have AS external
routes.

But in the book "OSPF Complete Implementation",section
11.5, we are asked to check the external path
preference mentioned in section 16.4.1 also.

Which method are we supposed to follow.

rgds
Alex

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