[c-nsp] OSPF area design question

[Terry Baranski]

Marcel Lammerse wrote:

> Ok, if you have that area 1 with 15 routers. Would it be 
> a good idea to keep them all in one area, or would it make 
> sense to assign 15 different area numbers and make each of 
> them a separate area (NSSA in this case). Because, I figured, 
> an update from one of the router will be flooded throughout 
> the entire area which is totally unnecessary.
> 
> I like to know whether the extra configuration and administrative
> overhead is worth saving on unnecessary update floods and cpu 
> cycles processing them.

Depends on how much routing churn you expect in your network.  If each
site advertises a single subnet that is only "withdrawn" when that
site's WAN link goes down, things should be pretty quiet overall.  The
less churn you expect, the less the "one area per site" technique makes
sense in a hub & spoke topology (IMO). 

I worked on a ~50 site hub & spoke network (one spoke, area 0) last year
and divided the spokes into 2 separate areas in what I thought was a
reasonable balance between the two extremes.

-Terry