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300-410 Practice Question: A DMVPN phase 3 network with IPv6 over IPv4…
A DMVPN phase 3 network with IPv6 over IPv4 tunnels is experiencing spoke-to-spoke tunnel failures. Hub router R1 has the following relevant configuration: interface Tunnel0 ipv6 address 2001:DB8:1::1/64 tunnel source GigabitEthernet0/0 tunnel mode gre multipoint ip nhrp network-id 1 ip nhrp map multicast dynamic ipv6 nhrp map multicast dynamic. Spoke router R2 shows: R2# show dmvpn detail Legend: Attrb -> S: Static, D: Dynamic, I: Incomplete NHRP domain: 1 Interface: Tunnel0, IPv4 NHRP Details Type:Spoke, Total NBMA Peers: 1 # Ent Peer NBMA Addr Peer Tunnel Add State UpDn Tm Attrb 1 192.0.2.2 2001:DB8:1::2 UP 00:10:00 D. What is the root cause?
⚠ Common exam trap
Cisco often tests the distinction between Phase 2 (where `ip nhrp map multicast dynamic` alone enables spoke-to-spoke tunnels) and Phase 3 (which additionally requires `ip nhrp redirect` on the hub and `ip nhrp shortcut` on spokes), causing candidates to overlook the missing redirect command.
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 is missing the ip nhrp redirect command under Tunnel0.
In DMVPN Phase 3, spoke-to-spoke tunnels rely on the hub to send NHRP Redirect messages to trigger shortcut creation. The hub's configuration is missing the `ip nhrp redirect` command under Tunnel0, which prevents it from informing the spoke that a better path exists directly to another spoke. Without this redirect, the spoke never initiates an NHRP Resolution Request to build a direct tunnel, causing spoke-to-spoke communication to fail.
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 is missing the ip nhrp redirect command under Tunnel0.
Why this is correct
This command enables NHRP redirect messages, which are essential for phase 3 spoke-to-spoke shortcut establishment.
- ✗
The spoke is missing the ip nhrp shortcut command under Tunnel0.
Why it's wrong here
While the spoke also needs this command, the hub's missing redirect is the primary cause here.
- ✗
The tunnel mode should be gre multipoint on the spokes.
Why it's wrong here
Spokes can use point-to-point GRE tunnels; multipoint is only required on the hub.
- ✗
IPv6 NHRP is not supported on DMVPN phase 3.
Why it's wrong here
IPv6 NHRP is supported on DMVPN phase 3 with appropriate configuration.
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.
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.
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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.