Design issue with OSPF

[kreinz.robert]

Hi all,

I have following problem and I am not sure if I can solve this:

I have two Backbone Routers (Area0) and they are connected to a NSSA area. The NSSA area is connected in a "chain" starting from the first Backbone Router and terminating at the second one.

The issue I have is the traffic going inside, from Area 0 to the NSSA area. The backbone routers are routing all traffic directly to the connected NSSA area, even if the cost through Area0 and the second Backbone Router would be better for some destinations.

Is there any chance to overcome this issue?

Thanks in advance,

Robert

[ariela]

Hi Robert,

if I well understand, your NSSA ABR choose external route instead of internal, isn't it?

please post your IOS versions (NSSA ABR).

Thanks

Andrea

[kreinz.robert]

Hi Ariela,

The NSSA ABR has IOS 12.2(25)S9 (7304 NSE100)

It's the other way around:

The NSSA ABR choose always the directly (internal) way through the connected NSSA Area instead using the external way through area 0 to the second NSSA ABR, where the costs to reach the destination are better.

Thanks,

Robert

[Richard Burts · Accepted solution]

Robert

You have encountered one of the principles of OSPF. An OSPF router will always prefer an intra-area route (route within the area) to an inter-area route (route between areas). When an OSPF router is making a routing decision and has a choice of an intra-area route and an inter-area route it will choose the intra-area route without any consideration of metrics or anything else. I do not know of any way to change this behavior.

HTH

Rick

[ariela · Accepted solution]

Hi Robert,

http://www.cisco.com/en/US/tech/tk365/technologies_q_and_a_item09186a0080094704.shtml#q13

The suggestion is: use two OSPF processes. But pay attention!

HTH

Andrea

[kreinz.robert]

Thanks all for the useful replies!

Robert