[c-nsp] OSPF, summarization, areas etc.

[Jon Lewis]

On Mon, 19 Nov 2007, Primoz Jeroncic wrote:

> Until recently we had all our network in one single area (not area 0). Now I
> moved our backbone to area 0, while keeping most of spokes in old area
> (area 100).
>
> I will be moving these spokes to different areas later on, but I would like to
> clarify few things first.
> So currently our config looks like this:
>
> router A -- area 100 - Router B - area 0 - Router C - area 200 - Router D
> router E -- area 100 - |
>
> Now my question. I understood all this so, that on Router D (in area 200) I
> wouldn't see all subnets in area 100, but summarized networks or even no area
> 100 networks. Obviously I'm wrong, or I'm doing something wrong, since I still
> see same amount of routes on router D as I did before, when whole network was
> in same area (area 100), even if I do summarization on Router B for networks
> behind Router A and/or E.
>
> PS: Config for OSPF is really simple standar thing...
>
> router ospf 1
> log-adjacency-changes
> redistribute connected subnets
> redistribute static subnets
> network x.x.x.x 0.0.0.0 area 0
> network y.y.y.y 0.0.0.0 area 100
> network z.z.z.z 0.0.0.0 area 100
> !
> ! and for summarization on router B
> area 100 range 10.10.0. 255.255.0.0

Assuming most of your network's routes come from redistribution of static 
and connected, these are type 2 external routes and will be sent into all 
regular areas.  Summarization of these types of routes can only be done on 
the routers that redistribute them into OSPF, and based on the config you 
posted, you're not doing that.

If you were to make areas 100 and 200 into NSSA's you would see a 
reduction of OSPF routes in those areas and still be able to redistribute 
static and connected from them into their respective areas and the 
backbone.

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  Jon Lewis                   |  I route
  Senior Network Engineer     |  therefore you are
  Atlantic Net                |
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