[c-nsp] OSPF NSSA question

[Ruben Alvarez]

Yes the routers in area 1 are set to redistribute connected and static.
They do DSL aggregation and if you can imagine I need some flexibility with
those addresses (approx /20.)  I'll move IP pools and /30 -/29 networks from
router to router as customers come and go.

I like how it's setup now because area 0 gets a few summarized routes and
have the flexibility to let the ABR dynamically do the routing for the
aggregation routers.  Only downside is the aggregation routers get all the
N2 routes when a default route is sufficient.  I'm reading about the "area 1
no-redistribution" command.  It reads external routes will not be flooded
into the NSSA.  So I read that as a router will advertise its routes and not
the routes it receives from other routers.  But wouldn't aggregationrouter1
still receive routes from aggregationrouter2?  It just wouldn't re-advertise
them.

I'm thinking the best plan would be to have each router in its own area.  As
far as what I read about stub, I can't redistribute static or connected
routes into OSPF which is the whole reason why I'm doing this.  Someone said
a stub area can have multiple routers.  Wikipedia says it can't.  

" A stub area is an area which does not receive external route
advertisements. It may be configured to reduce many route advertisements
into an area when the routing table consists of mostly external routes.
Instead of the external routes, a default route is advertised to the stub
area. A stub area has only one OSPF router, cannot contain an AS boundary
router (ASBR) and routes cannot be distributed from other protocols into the
stub area."

Can someone confirm that?

Thanks all.



-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Jon Lewis
Sent: Wednesday, July 22, 2009 10:44 AM
To: Laurent Geyer
Cc: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] OSPF NSSA question

On Wed, 22 Jul 2009, Laurent Geyer wrote:

> If you're set on keeping the routers in a NSSA you could simply
> disable redistribution into the NSSA area by adding
> 'no-redistribution' to the area config.
>
> This will effectively keep type 5 LSAs from being advertised into the
NSSA.
>
> Realistically it makes more sense to turn the areas into totally
> stubby areas. I don't see what benefit you gain from keeping the
> routers in a NSSA.

Simpler configuration?  I'm going to assume the routers in the NSSA are 
exporting (probably static and or connected) routes into OSPF and can't do 
this in a regular stub area.

I have an NSSA for some layer 3 switches doing this.  The switches can 
handle a limited number of routes and really don't gain anything by 
carrying our full internal routes.

----------------------------------------------------------------------
  Jon Lewis                   |  I route
  Senior Network Engineer     |  therefore you are
  Atlantic Net                |
_________ http://www.lewis.org/~jlewis/pgp for PGP public key_________
_______________________________________________
cisco-nsp mailing list  cisco-nsp at puck.nether.net
https://puck.nether.net/mailman/listinfo/cisco-nsp
archive at http://puck.nether.net/pipermail/cisco-nsp/