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I am doing OSPF labs right now and have been reading the explanation for 6.30 (Page 167) which states:

[..] When the route moves between areas, each ABR originates a Type-4 ASBR Summary LSA advertising their reachability to the ASBR. This means that for all Type-5 External LSA inter-area lookups OSPF would require  Ext_Routes + Num_ABRs + Num_Routers LSAs. [..]

In my opinion, if the first sentence holds true, meaning that each ABR generates Type-4 LSA for each ASBR (described by LSA-1), then the number of LSAs is Ext_Routes + (Num_Routers * Num_ABRs) + Num_Routers.

On the next page we read:

[..] Let's suppose for the sake of argument that each ABR connecting to the NSSA to area 0 did do a translation of Type-7 to 5. This would mean for all inter-area lookups on Type-5 External LSAs that were translated from Type7-, there would be (NSSA_Routes * Num_ABRs) + Num_ABRs + Num_Routers LSAs [..]

I think, that if there is no LSA Type-4 generated on ABR for NSSA, the Num_ABRs in the formula is not neccessary, it should be:  (NSSA_Routes * Num_ABRs) + Num_Routers

Anyone willing to comment on this?

Many thanks, 

Sebastian

Guys,

Some of you may have come up with a slightly modified solution than SG offers using "route summrization" on R3.

This will make R5 prefer route to 150.1.9.9 via R6 because /32 host route will be preferred to summarized route from R3. Works for failover too.

# R3

router ospf 1

area 2 range 150.1.9.0 255.255.255.0

Tom