300-410 Layer 3 Technologies Practice Question
A network engineer is troubleshooting a DMVPN Phase 3 network using EIGRP as the routing protocol. Spoke routers are unable to establish direct spoke-to-spoke tunnels. The engineer verifies that NHRP registration is successful and that the hub has routes to all spokes. Which action is most likely to resolve the issue?
⚠ Common exam trap
The trap here is focusing on EIGRP or tunnel configuration when the issue is actually NHRP Phase 3 specific commands.
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
✓
Verify that the hub is configured with ip nhrp redirect and the spokes with ip nhrp shortcut.
In DMVPN Phase 3, spoke-to-spoke tunnels require ip nhrp redirect on the hub and ip nhrp shortcut on the spokes. These commands allow the hub to redirect traffic and the spokes to create shortcut routes. Without them, spokes will continue to route through the hub, even if NHRP registration is successful.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Ensure that the tunnel interfaces on all routers are configured with the same tunnel key.
Why it's wrong here
The tunnel key is used to identify a tunnel and is not required to match for DMVPN operation. In fact, different keys can be used on different tunnels. The lack of spoke-to-spoke tunnels is typically due to NHRP resolution or routing issues, not tunnel key mismatch.
- ✓
Verify that the hub is configured with ip nhrp redirect and the spokes with ip nhrp shortcut.
Why this is correct
In DMVPN Phase 3, the hub must have ip nhrp redirect to inform spokes of a better path, and spokes must have ip nhrp shortcut to install shortcut routes. Without these, spoke-to-spoke tunnels will not be established. This is a common misconfiguration that prevents direct spoke communication.
- ✗
Change the EIGRP network type on the tunnel interfaces to point-to-multipoint.
Why it's wrong here
The EIGRP network type affects neighbor adjacency and DR/BDR election. In DMVPN, the tunnel network type is often point-to-multipoint by default, but changing it does not enable spoke-to-spoke tunnels. The issue is with NHRP and routing, not EIGRP network type.
- ✗
Configure EIGRP stub routing on the spoke routers.
Why it's wrong here
EIGRP stub routing is used to limit query propagation and is often configured on spokes in DMVPN. However, it does not directly enable spoke-to-spoke tunnels. The issue is likely related to NHRP resolution or routing, not stub routing. In fact, stub routing might prevent the hub from advertising spoke routes, but that is not the cause of the failure here.
Visual reference
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
EIGRP Route Summarization and Filtering
Key term
DMVPN Phase 3
DMVPN Phase 3 is a Cisco networking technology that allows branch offices to connect directly to each other without always going through a central hub, but with smarter routing that lets the hub control the traffic paths more efficiently.
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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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.