>I don't know about the genius part. >:-) But, you've described the
>initial scenario I was asking about. In my original post I wasn't
>suggesting that this would be a good design by any means. I simply was
>wondering if it was possible and how you'd configure it.
>
>In this particular case, the hub router is participating in 20 areas
>which would cause it to be very busy, especially if the network wasn't
>very stable. It would be better to extend area zero across the WAN
>links to insulate the hub router from any instability in the outlying
>areas.
>
>John
You definitely are describing an "it depends" situation. Without
considering other factors, the number of areas per physical router
isn't a major performance consideration.
The reason for restricting it is that in general, with increasing
numbers of areas, you are more likely to need to do a SPF calculation
simultaneously in more than one area. If the areas are highly
stable, or have very few links in them, the effect of the SPF may be
minimal.
Another consideration is the degree to which inter-area routes
propagate to other non-backbone areas. Interarea routes do not
necessarily trigger the most intensive part of SPF, the Dijkstra. By
"not necessarily," I don't know how Cisco's implementation actually
reacts to receiving an inter-area LSA without any accompanying
intra-area changes.
You also need to consider the CPU power of the routers involved. The
most areas I've configured were on 7000's, not all that fast a CPU
box, typically with seven nonzero areas each. The nonzero areas were
very stable optically wired campuses.
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