OSPF over NBMA Networks

In general, there are 5 ways to deal with it.

1. Fully meshed topology. Drawback is you have to manage n(n-1)/2 PVCs
2. Estabish each PVC as an individual point-to-point network with its own subnet. Most easily managed, requires more processing power on routers.
3. Using the neighbor command. The oldest solution for pre-10.0 version IOS.

Example
Hub site router
router ospf 1
network 172.16.0.0 0.0.255.255 area 0
neighbor 172.16.2.2 ! Default priority 0, means spoke router will never be DR
neighbor 172.16.2.3

Spoke site Router A
router ospf 1
network 172.16.0.0 0.0.255.255 area 0
neighbor 172.16.2.1 priority 10 ! It makes the hub site router a DR

4. ip ospf network broadcast. Cause the NBMA cloud to view as broadcast multiaccess network.

Example
Hub site router
interface Serial0
ip ospf network broadcast
ip ospf priority 10 ! It makes the hub site router a DR

Spoke site Router A
interface Serial0
ip ospf network broadcast
ip ospf priority 0 ! means spoke router will never be DR

5. ip ospf network point-to-multipoint. Treat the PVCs as a collection of point-to-point links. Therefore no DR/BDR election takes place.

Example
Hub site router
interface Serial0
ip ospf network point-to-multipoint non-broadcast

Spoke site Router A
interface Serial0
ip ospf network point-to-multipoint non-broadcast