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300-410 Practice Question: In a DMVPN Phase 2 network with EIGRP, R1 (hub)…
In a DMVPN Phase 2 network with EIGRP, R1 (hub) and R2 (spoke) are configured. R2's tunnel interface has 'ip nhrp redirect' enabled. R3 (another spoke) can ping R2's tunnel IP, but when R3 tries to reach a subnet behind R2, traffic is forwarded to R1 instead of directly to R2. What is the root cause?
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 (hub) does not have 'ip nhrp redirect' enabled on its tunnel interface, so it does not send redirect messages to R3, preventing direct spoke-to-spoke tunnel establishment.
In DMVPN Phase 2, spoke-to-spoke tunnels are established using NHRP redirect. However, if the hub does not have 'ip nhrp redirect' enabled, it will not send redirect messages to spokes. Without redirect, spokes will not learn the direct path to other spokes and will forward traffic through the hub.
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 (hub) does not have 'ip nhrp redirect' enabled on its tunnel interface, so it does not send redirect messages to R3, preventing direct spoke-to-spoke tunnel establishment.
Why this is correct
Correct. In Phase 2, the hub must have NHRP redirect enabled to inform spokes of direct paths. Without it, spokes forward traffic through the hub.
- ✗
R2 has 'ip nhrp shortcut' disabled, preventing direct tunnel establishment.
Why it's wrong here
Incorrect. 'ip nhrp shortcut' is used on spokes to accept redirects, but the issue is that redirects are not being sent.
- ✗
R3 has a static route pointing to R1 for the subnet behind R2.
Why it's wrong here
Incorrect. Static routes could cause this, but the question focuses on NHRP configuration.
- ✗
EIGRP is not redistributing the subnet behind R2 to R3.
Why it's wrong here
Incorrect. If R3 can ping R2's tunnel IP, routing is working. The issue is path selection.
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
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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