[c-nsp] OSPF Campus Design : Excessive SPF Runs

[Jason LeBlanc]

Hello,

We currently have Layer 3 Routed Access configured at all of our Metro Campus locations.  There are a few obvious deviations from the best practice design guides.   The current setup is:

Core --> 	Datacenter Distribution --> | (fiber connect) | --> 	Building Distribution --> 	Access
(backbone)	(ABR)										(ASBR)					(OSPF enabled access switch)

The Cisco best practice is:

Core --> 	Distribution --> 	Access
(backbone)	(ABR)			(OSPF enabled access switch)

We are running NSSA with no-summary and the range command on the Datacenter Distribution routers.  Each floor has 2 access switches (w/ OSPF running) which each have a link back to the Building Distribution router.  Vlans on each box on each floor are mutually exclusive.

Symptoms: 
Lots of SPF re-calculations, NTP failing from Datacenter Distro -> Building Distro, and users reporting loss of their shared drives. 

router-a#sh ip ospf stat   
  Area 0.0.0.0: SPF algorithm executed 7865 times
  Area 192.8.208.0: SPF algorithm executed 386 times
  Area 192.70.0.0: SPF algorithm executed 563 times
  Area 192.100.0.0: SPF algorithm executed 93076 times


Questions:
Should we be advertising (passively or non-passively) L3 Vlans into OSPF?
Should we be doing Totally NSSA's instead of NSSA's?
	If not is there a way to get the DR in NSSA to advertise a single route back as default route?
Should we be sending each campus distribution router directly to the Core so that its the 3 hops?
Do you suggest tuning the OSPF dead interval to achieve subsecond convergence?


Any help advise is greatly appreciated!

Regards,

//LeBlanc