A DMVPN spoke router tunnel is up and passing traffic, but it cannot establish an EIGRP neighbor relationship with the hub router. Which solution resolves this issue?

Question

Options

• AEnable EIGRP Split Horizon on the hub tunnel interface.
• BRemove the EIGRP stub configuration on the spoke tunnel interface.
• CEnable the EIGRP next hop self feature on the hub tunnel interface.
• DConfigure the dynamic NHRP multicast map on the hub tunnel interface.

• A
  3% (1)
• B
  5% (2)
• C
  8% (3)
• D
  84% (31)

Explanation

EIGRP uses multicast (224.0.0.10) for Hello and Update packets. In DMVPN, the hub's tunnel interface must know how to replicate multicast traffic to all registered spokes - otherwise EIGRP Hellos sent by the hub never reach the spokes, and the neighbor relationship never forms.

The fix is adding ip nhrp map multicast dynamic on the hub's tunnel interface. This command tells NHRP to automatically add each spoke as a multicast recipient when it registers, so EIGRP multicast frames are replicated and forwarded correctly.

Why the other options are wrong:

• A - Split horizon should be disabled (no ip split-horizon eigrp <AS>) on the hub, not enabled. Enabling it would break spoke-to-spoke route advertisements.
• B - EIGRP stub limits a router's advertised prefixes but does not prevent neighbor formation. Removing stub would not fix a missing adjacency.
• C - next-hop-self ensures proper routing of spoke-to-spoke traffic, but it is a routing correctness fix, not a neighbor establishment fix.

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