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300-410 Practice Question: A DMVPN network with EIGRP as the routing…
A DMVPN network with EIGRP as the routing protocol is experiencing spoke-to-spoke tunnel failures. Spoke routers R1 and R2 are both connected to hub R3. R1 shows: 'show ip nhrp' lists R2's NBMA address, but 'show ip eigrp neighbors' does not show R2. R1's configuration: interface Tunnel0 ip nhrp network-id 1 ip nhrp nhs 10.0.0.3. What is the root cause?
⚠ Common exam trap
Cisco often tests the misconception that NHRP and EIGRP are automatically linked; the trap here is that candidates assume a working NHRP mapping implies EIGRP adjacency, but EIGRP requires explicit interface-level configuration to send hellos over the tunnel.
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
✓
R1 has no EIGRP configuration on the tunnel interface, so it does not send hellos over the tunnel.
R1's 'show ip nhrp' lists R2's NBMA address, confirming NHRP phase 2/3 spoke-to-spoke resolution is working. However, 'show ip eigrp neighbors' does not show R2, indicating EIGRP adjacency is not established. Since R1's tunnel interface lacks EIGRP configuration (no 'ip eigrp <as-number>' under Tunnel0), it does not send EIGRP hellos over the tunnel, preventing neighbor formation even though NHRP can dynamically map spoke addresses.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
R1 has no EIGRP configuration on the tunnel interface, so it does not send hellos over the tunnel.
Why this is correct
EIGRP must be enabled on the tunnel interface to establish neighbor relationships over it.
- ✗
R2's NHRP registration is incomplete, so R1 cannot reach R2's NBMA address.
Why it's wrong here
NHRP shows R2's NBMA address, so registration is complete.
- ✗
The hub R3 is not configured to forward EIGRP packets between spokes.
Why it's wrong here
In DMVPN, spoke-to-spoke tunnels are direct; the hub does not forward EIGRP packets.
- ✗
R1's tunnel interface has an ACL that blocks EIGRP packets.
Why it's wrong here
No ACL is mentioned.
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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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.