OSPF: Network Types and NBMA Caveats

Use of OSPF across Frame Relay can be challenging, here is a list of things to check when looking at OSPF configuration over Frame Relay when OSPF network types do not match on the various routers:

  • Make sure Hello/Dead timers match
  • Make sure that all routers on a NBMA use an OSPF network type that uses a DR or NOT
  • If a Dr is used, the DR and BDR must have a PVC to each and every other router so they can forward LSUs to those devices.
  • It is best practice to configure neighbor commands on both routers

Also, if the design allows for point to point subinterfaces use those and  take the default OSPF network type of point to point, no additional work should be required for it to work across an NBMA network.

If multipoint subinterfaces are required adding the ip ospf point-to-multipoint command on all routers works without requiring additional effort to manually define neighbors or worry about which router becomes DR.

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