Question

A network engineer manages a DMVPN Phase 1 hub-and-spoke topology running EIGRP over the multipoint tunnel interface Tunnel0 on the hub. Each spoke forms an EIGRP adjacency with the hub and advertises its LAN prefix successfully. However, the engineer notices that no spoke learns the LAN prefixes of any other spoke, even though the hub shows all spoke routes in its topology and routing table. The hub's Tunnel0 has no distribute-lists or route-maps applied. What is the most likely cause?

Accepted Answer

EIGRP split horizon is enabled by default on the hub's multipoint tunnel interface, preventing routes learned on Tunnel0 from being re-advertised out the same interface.

Answer

The hub is missing the 'no ip next-hop-self eigrp' command, so spoke routes are being suppressed by route poisoning.

Answer

Auto-summarization on the hub is collapsing the spoke prefixes into a single classful route that the spokes reject.

Answer

The spokes have a higher administrative distance configured for EIGRP, causing them to discard the hub-advertised routes.