OSPF: DR over WAN and Network Types

Using a DR makes sense on a LAN since it would improve LSA flooding efficiency while NOT having a DR on point to point WAN links also makes sense.  If there is only one other router on the other end of the point to point connection there is no need to optimize LSA exchange on that link.

NBMA networks could go either way, and OSPF has multiple options for dealing with those types of WAN connections.

The OSPF network type determines the following:

  • whether the router tries to elect a DR on that interface
  • whether the router must statically configure a neighbor or find neighbors using multicast Hello packets
  • whether more than two neighbors should be allowed on the same subnet

networktypesospf.PNG

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