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300-410 Practice Question: A DMVPN Phase 2 network is configured with EIGRP…
A DMVPN Phase 2 network is configured with EIGRP as the routing protocol over the tunnel interface. Spoke routers have `no ip split-horizon eigrp 100` configured on the tunnel interface. Unexpectedly, spoke-to-spoke tunnels are established, but EIGRP routes learned from one spoke are not installed in the routing table of another spoke, even though NHRP resolution works. 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 router has `ip next-hop-self eigrp 100` enabled by default, which sets the next-hop to the hub, preventing direct spoke-to-spoke routes.
In DMVPN Phase 2, spoke-to-spoke tunnels require that EIGRP next-hop self behavior is disabled or that the next-hop is changed. By default, EIGRP advertises routes with the next-hop set to the advertising router's tunnel IP. When a spoke learns a route from another spoke via the hub, the next-hop is the hub's tunnel IP, not the originating spoke. The spoke must have `no ip next-hop-self eigrp 100` on the hub's tunnel interface to preserve the original next-hop, allowing direct spoke-to-spoke communication.
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 router has `ip next-hop-self eigrp 100` enabled by default, which sets the next-hop to the hub, preventing direct spoke-to-spoke routes.
Why this is correct
Default EIGRP next-hop self on the hub causes spokes to see the hub as next-hop, not the originating spoke.
- ✗
The spoke routers need `ip split-horizon eigrp 100` enabled to advertise routes to other spokes.
Why it's wrong here
Split horizon prevents routes from being advertised back out the same interface; disabling it is correct for DMVPN.
- ✗
EIGRP does not support DMVPN Phase 2; OSPF must be used for spoke-to-spoke routing.
Why it's wrong here
EIGRP works with DMVPN Phase 2 when properly configured.
- ✗
The NHRP authentication is mismatched, so EIGRP packets are dropped.
Why it's wrong here
NHRP authentication does not affect EIGRP packet forwarding.
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
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.