Understanding OSPF Networ ...
    09 January 08

    Understanding OSPF Network Types

    Posted byINE

    By adjusting the hello/dead timers you can make non-compatible OSPF network types appear as neighbors via the "show ip ospf neighbor" but they won't become "adjacent" with each other.  OSPF network types that use a DR (broadcast and non-broadcast) can neighbor with each other and function properly.  Likewise OSPF network types (point-to-point and point-to-multipoint) that do not use a DR can neighbor with each other and function properly.  But if you mix DR types with non-DR types they will not function properly (i.e. not fully adjacent).  You should see in the OSPF database "Adv Router is not-reachable" messages when you've mixed DR and non-DR types.

    Here is what will work:

    Broadcast to Broadcast
    Non-Broadcast to Non-Broadcast
    Point-to-Point to Point-to-Point
    Point-to-Multipoint to Point-to-Multipoint
    Broadcast to Non-Broadcast (adjust hello/dead timers)
    Point-to-Point to Point-to-Multipoint (adjust hello/dead timers)

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