NSSA with two ABRs

[m.gamal]

i am having an OSPF network, and one of the areas is NSSA area, when i try to make the area with two ABRs , this thing fails, and other routers in the core area doesn't see the networks in the NSSA area from the two ABR, even the network is symetrical and all costs are equal

so my question is , can i have two ABRs for a NSSA area..??

[mark-obrien]

I have a NSSA with two ABRs. It works fine.

Mark

[m.gamal]

mark

i tried it in a lab environment..and it didn't work.

is there any extra config. i shall do?

do u have document for this case.?

Thanks

[vincent-n]

Becareful here cause from memory, NSSA is a Cisco proprietary thing so it will not work with other vendor.

[jmcoffey]

You can have 2 ABR in an NSSA area. The problem most people run into though is that only the higher router-ID will do type-7 to type-5 translation for external routes. The other ABR will basically act as a hot standby router for external routes in case the other ABR fails. All incoming traffic to external routes come though 1 router. Interarea routes will be OK because both ABRs will distribute these type 3 and 4 LSAs to the backbone. It screws up your external routing causing extra hops and unsymetrical routing. You do not have these problems with just one ABR. But we all need redundancy. So you are between a rock and a hard place using an NSSA with two ABRs.