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selectively redistribute in some OSPF areas, not all

gnijs
Level 4
Level 4

Hello,

I might have a strange question: is it possible to selectively redistribute into an area when your router has multiple areas ??
Let me explain: we have a NSSA area composed of 4 routers: lets say routers A and B connect to the backbone area 0.0.0.0, router C & D have a RIP/static/EIGRP connection and redistribute some (very limited) routes into the NSSA (hence NSSA).
However, recently we have started to deploy BGP additionally on our core routers A and B. They receive BGP routes and redistribute them into the backbone. However, by default, they ALSO push (all) these routes into the NSSA area, which i in fact don't want and which is not needed (since A & B already put a default into the NSSA area by design).
Is there a way to prevent this from happening ?

Probably area filter ?

area NSSA filter-list prefix DEFAULT out 

or something like that.....

4 Replies 4

OSPF: Area range vs Summary address | IPNET
two command you have 
area range
summary address 
check link above and see which option is suitable for you.
thanks 
MHM 

Hi,

so you do redistribution on NSSA ABR routers which are "A" and "B". Use just below command:

area X nssa no-redistribution where X is nssa area number. In this case NSSA ABR (which is also OSPF ASBR due to BGP redistribution) will create type5 LSA of external subnets (redistributed subnets) for non-NSSA areas , but not type7 for NSSA area.

Note that, OSPF filter-list is used on ABR for inter-area filtering (type3 LSA). Area range command is also for type3 creation (based on another area type1/2).

HTH,
Please rate and mark as an accepted solution if you have found any of the information provided useful.

Hello
I agree with @Kanan Huseynli rtrs A/B are the ASBR for area 0 for the bgp routes,
Now you state you do not want these bgp routes to be advertised into the NSSA, so to accomplish this those bgp routes which are at present originate as external type 5 LSa's in area 0 are being converted into type 7 LSAs when entering the NSSA.

So you need to negate this external LSA translation into the NSSA on rtr A/B .
Rtr C/D should still have reachability via the default routes you say they are receiving in the NSSA.

Example rtr A/B   (area 10 is the nssa)
router ospf 100
area 10 nssa no-redistribution
area 10 nssa no-summary <-- assumption this is already applied?)


Please rate and mark as an accepted solution if you have found any of the information provided useful.
This then could assist others on these forums to find a valuable answer and broadens the community’s global network.

Kind Regards
Paul

can you share the topology please ?

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