Cisco Certified Internetwork Expert (CCIE) Practice Test

What effect does the ip nhrp map multicast dynamic command have?

1. It configures a hub router to reflect the routes it learns from a spoke back to other spokes through the same interface

2. It enables a GRE tunnel to dynamically update the routing tables on the devices at each end of the tunnel

3. It configures a hub router to automatically add spoke routers to the multicast replication list of the hub

4. It enables a GRE tunnel to operate without the IPsec peer or crypto ACLs

The correct answer is: It configures a hub router to automatically add spoke routers to the multicast replication list of the hub

The command "ip nhrp map multicast dynamic" is primarily associated with the setup of Non-Broadcast Multi-Access (NBMA) networks using NHRP (Next Hop Resolution Protocol). This command specifically enables a hub router in a DMVPN (Dynamic Multipoint Virtual Private Network) configuration to dynamically recognize and register multicast traffic from the spoke routers. When this command is enabled on the hub router, it allows the hub to automatically include any spoke routers in the multicast replication list. This facilitates the transmission of multicast packets to all connected spokes without requiring manual configuration for each new spoke that joins the network. In a typical DMVPN setup, spokes can communicate directly with each other using multicast traffic directed over the hub. By using this command, the hub router can efficiently manage multicast traffic and ensure that all spokes receive the relevant broadcasts or multicast traffic. The dynamic addition feature enhances scalability since as new spoke routers are added, they will automatically be included in the multicast routing without further intervention. This understanding of multicast behavior and dynamic registration is critical for network engineers working with DMVPN, as it directly impacts the efficiency and performance of the network.