A DMVPN single hub topology is using IPsec + mGRE with OSPF.
What should be configured on the hub to ensure it will be the designated router?
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A. B. C. D.D.
In a DM VPN (Dynamic Multipoint VPN) single hub topology using IPsec + mGRE with OSPF, there are multiple spoke routers that communicate with the hub router over the same IPsec VPN tunnel. The hub router acts as a hub for all the spoke routers, and it is responsible for forwarding the packets between the spoke routers.
In this scenario, OSPF (Open Shortest Path First) is used as the routing protocol to dynamically learn and distribute the routes between the hub and the spoke routers. OSPF uses a designated router (DR) and a backup designated router (BDR) to reduce the number of adjacencies in the network and to improve the scalability of the network.
To ensure that the hub router is selected as the DR in the DM VPN single hub topology, we can configure the OSPF priority of the hub router to a higher value than the other routers in the network. This will cause the hub router to become the DR, and it will be responsible for flooding the LSAs (Link State Advertisements) to the other routers.
The correct answer to the question is D - OSPF priority greater than 1. We should configure the OSPF priority of the hub router to a value greater than 1 to ensure that it becomes the DR. The OSPF priority range is from 0 to 255, with 0 being the lowest priority, and 255 being the highest priority. A priority of 0 means that the router cannot become the DR or BDR.
Option A - route map to set the metrics of learned routes to 110 is not a valid configuration to ensure that the hub router becomes the DR. Changing the metric value will not affect the DR election process.
Option B - tunnel interface of the hub with ip nhrp ospf dr is also not a valid configuration to ensure that the hub router becomes the DR. The ip nhrp ospf dr command is used to configure the hub router as the DR for NHRP (Next Hop Resolution Protocol), not OSPF.
Option C - OSPF priority to 0 is also not a valid configuration to ensure that the hub router becomes the DR. A priority of 0 means that the router cannot become the DR or BDR.