Hani Mustafa hani.mustafa at noorgroup.net
Tue Feb 10 20:19:43 EST 2004

> distribute-list ?

With OSPF, distribute lists do not block actual LSA's. They merily prevent them from being used in the routing table. LSA's will still be propagated to other routers.

Try using "area 1 filter-list prefix <prefix-list>".

I have played around with this scenario of yours and have found out that if you set up area 1 as NSSA, and also include the loopback (assuming its your router-id) in your network commands, R1 will automatically do a recursive look-up and loadbalance for the external route (even though there will be one OSPF external type-5 LSA in R1's database, which conforms with what Oliver says).

interface loopback 0
  ip address

router ospf 1
  area 1 nssa
  network area 1
  <... other network commands ...>
  redistribute static subnets

If you do a "show ip ospf database external" at this point on R1, you will find one LSA for the redistributed route, with the "Forward Address" set to R4's router-id. The router then looks at the 2 Summary LSA's for R4's router-id (advertised by R2 and R3), and loadbalances between both of them (provided they're equal).

~Hani Mustafa

> > One main reason why I ran NSSA was because R1 & R4 are
> > also redistributing static/connected routes and I
> > would like to limit the number of external routes that
> > enter R4 since R4 can basically just pass the traffic
> > to either R1/R2 and doesn't need to see everything
> > else that R1 redistributes.
> > 
> > Do you have any idea what could be done to achieve
> > this effect? Maybe some filtering in normal OSPF area
> > mode?

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