300-410 Layer 3 Technologies Practice Question
A network engineer is troubleshooting a DMVPN Phase 3 network using Cisco IOS-XE routers. The hub router is configured with `ip nhrp redirect` and spoke routers with `ip nhrp shortcut`. A spoke router is unable to establish a direct spoke-to-spoke tunnel for a specific destination. Which action should the engineer take to resolve this?
⚠ Common exam trap
The trap here is focusing on NHRP or multicast configuration when the missing piece is often the routing table entry on the spoke that points to the hub, which is required to trigger the redirect.
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
✓
Ensure that the spoke routers have a route to the destination network via the hub.
DMVPN Phase 3 relies on NHRP redirects from the hub to trigger spoke-to-spoke shortcuts. For the spoke to send initial traffic to the hub and receive a redirect, it must have a route to the destination via the hub. This route is typically learned through the routing protocol running over the DMVPN. Without it, the spoke cannot initiate the shortcut process.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Disable `ip split-horizon` on the hub's tunnel interface.
Why it's wrong here
Split horizon is relevant for distance-vector routing protocols like EIGRP or RIP to prevent routing loops. In DMVPN Phase 3, the issue is not split horizon but rather the presence of a route via the hub. Disabling split horizon might affect routing updates but does not directly enable shortcut tunnels.
- ✗
Configure `ip nhrp map multicast dynamic` on the hub.
Why it's wrong here
The `ip nhrp map multicast dynamic` command is used to enable dynamic multicast mapping on the hub for routing protocols, but it does not affect spoke-to-spoke shortcut tunnels. This command is typically already present in DMVPN configurations for multicast support. It is not the cause of the shortcut failure.
- ✗
Configure `ip nhrp nhs` on the spoke to point to the hub.
Why it's wrong here
The `ip nhrp nhs` command specifies the Next Hop Server (NHS), which is typically the hub. This is a fundamental configuration for DMVPN registration and is likely already configured. If it were missing, the spoke would not register at all, so it is not the specific cause of shortcut failure.
- ✓
Ensure that the spoke routers have a route to the destination network via the hub.
Why this is correct
For DMVPN Phase 3 shortcut tunnels to work, the spoke must have a route to the destination network pointing to the hub initially. When traffic is sent to the hub, the hub sends an NHRP redirect, and the spoke can then establish a direct tunnel. Without a route via the hub, the spoke cannot trigger the shortcut process.
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
DMVPN and FlexVPN Technologies
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.