hardMultiple ChoiceObjective-mapped
300-410 Practice Question: An engineer configures a DMVPN Phase 2 network
An engineer configures a DMVPN Phase 2 network. Spoke routers can communicate with the hub, but spoke-to-spoke tunnels do not form. The NHRP registration is successful, and the hub has the spoke's NBMA address. 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 spoke routers are missing the `ip nhrp redirect` command on the hub.
In DMVPN Phase 2, spoke-to-spoke tunnels require that the spoke routers have a route to the remote spoke's tunnel IP via the hub, and that the hub has NHRP redirect enabled. Without the redirect, the spoke does not know to initiate a direct tunnel.
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 spoke routers are missing the `ip nhrp redirect` command on the hub.
Why this is correct
In Phase 2, the hub must send NHRP redirect messages to inform spokes of better paths; without it, spokes send traffic through the hub.
- ✗
The spoke routers have different tunnel keys configured.
Why it's wrong here
Tunnel keys must match for the tunnel to form, but this would affect all tunnels, not just spoke-to-spoke.
- ✗
The spoke routers are using the same NHRP authentication string.
Why it's wrong here
NHRP authentication must match, but that is for registration; it does not prevent spoke-to-spoke tunnels specifically.
- ✗
The hub router has a lower MTU on the physical interface, causing fragmentation.
Why it's wrong here
MTU issues can cause problems, but they would affect all traffic, not just spoke-to-spoke tunnel establishment.
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.