hardMultiple ChoiceObjective-mapped
300-410 Practice Question: An engineer configures a DMVPN Phase 2 network
An engineer configures a DMVPN Phase 2 network. Spoke routers can communicate with the hub, but spoke-to-spoke traffic is not establishing dynamically. The engineer verifies that NHRP is configured and that the hub is configured as an NHRP server. Which is the most likely explanation?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The hub is not configured with 'no ip next-hop-self' for the routing protocol on the tunnel interface
In DMVPN Phase 2, spoke-to-spoke tunnels require that the spoke routers have a route to the remote spoke's tunnel IP address via the hub. This is achieved by the hub advertising the spoke's prefix with the next-hop set to the spoke's tunnel IP. However, if the hub does not configure 'no ip next-hop-self eigrp' (or similar for the routing protocol), the hub will set the next-hop to itself, preventing the spoke from directly reaching the remote spoke. This is a common edge case because the default behavior of routing protocols is to set the next-hop to the router's own IP.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The hub is not configured with 'no ip next-hop-self' for the routing protocol on the tunnel interface
Why this is correct
Correct. In Phase 2, the hub must not change the next-hop to itself; otherwise, spokes cannot build direct tunnels.
- ✗
NHRP authentication is mismatched between spokes
Why it's wrong here
NHRP authentication mismatch would prevent registration, not spoke-to-spoke traffic after registration.
- ✗
The spoke routers have not enabled NHRP redirect
Why it's wrong here
NHRP redirect is used in Phase 3, not Phase 2.
- ✗
The tunnel mode is set to GRE multipoint on the spokes
Why it's wrong here
Tunnel mode GRE multipoint is required on spokes, but this is not the cause of the issue.
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
Go deeper
Related to this question
Learn chapter
Introduction to ENARSI Exam and Network Fundamentals
Key term
DMVPN Phase 2
DMVPN Phase 2 is an advanced Cisco routing technology that allows spoke routers to communicate directly with one another without sending traffic through a central hub, using dynamic routing protocols and multipoint GRE tunnels.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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