OSPF is configured over a Frame Relay network as shown in the exhibit. All PVCs are active.
However, R1 and R3 fail to see all OSPF routes in their routing tables. The show ip ospf neighbor
command executed on R2 shows the state of the neighbors. What should be done to fix the problem?
A.
The ip ospf network non-broadcast command should be configured on each Frame Relay
interface.
B.
The ip ospf network broadcast command should be configured on each Frame Relay interface.
C.
The neighbor command should be configured under the OSPF routing process on all routers.
D.
The ip ospf priority value on the hub router should be set to 0.
E.
The ip ospf priority value on the spoke routers should be set to 0.
Explanation:
In an NBMA network topology, neighbors are not discovered automatically. OSPF tries to elect a
DR and a BDR due to the multi-access nature of the network, but the election fails since neighbors
are not discovered because NBMA environment doesn’t forward broadcast and multicast packets.
Neighbors must be configured manually to overcome these problems.
Also, additional configuration is necessary in a hub and spoke topology to make sure that the hub
routers, which have connectivity with every other spoke router, are elected as the DR and BDR.
You must set the spoke interfaces to an OSPF priority of zero, this ensures that the spokes will not
become the DR or BDR.