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 broadcast command should be configured on each Frame Relay
interface.
B.
The ip ospf network non-broadcast command should be configured on each Frame Relay
interface.
C.
The ip ospf priority value on the spoke routers should be set to 0.
D.
The ip ospf priority value on the hub router should be set to 0.
E.
The neighbor command should be configured under the OSPF routing process on all
routers.
Setting Priority to 0 will just force R2 to be the DR.
to “work” these would need to be set as two separate Point-to-point with sub-int
or as a “point-to-multipoint non-broadcast”
forcing all multicast traffic to be uni-cast instead.
in which case both C & E are used to manually define Neighbors
Please someone clarify for me how forcing R2 to be the DR would fix routing?
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•Hub-and-spoke environments should elect the hub as the DR or use point-to-point subinterfaces – which don’t require a DR
http://www.ccnpguide.com/ccnp-route-642-902-ospf/
NEVERMIND: i found my answer.
FR is broadcast…..DR are elected and multicast works.
in a point-to-multipoint like this…it makes sense to just force the hub to be DR in order to allow it to push route update LSA to the spokes.
Since the DR (the hub) sees the two spokes…it will tell them each about the other and it will work.
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You cant predict your spokes will have full visibility of the other spokes because of your frame relay topology. You set the spokes priorities to 0 so they cannot be DR or BDR. The Hub router assumes the BDR has full visibility of the network (it doesnt !) so as long as the BDR exists, it remains passive and listen for traffic from the DR. By having no BDR, the DR will send LSU updates to all the spokes !
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What’s more, part of the new 489Q 300-101 dumps for your reference:
https://drive.google.com/open?id=0B-ob6L_QjGLpZEE0S2YxR3ZMUWs
Best Regards!
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