hardMultiple ChoiceObjective-mapped
300-410 Practice Question: An engineer is troubleshooting a DMVPN phase 3…
An engineer is troubleshooting a DMVPN phase 3 network where spoke-to-spoke tunnels are not being established dynamically. The hub router has NHRP redirect enabled, and spokes have NHRP shortcut enabled. The engineer notices that when a spoke sends traffic to another spoke, the hub forwards the traffic but does not send an NHRP redirect. The hub's NHRP configuration includes the command 'ip nhrp redirect'. What is the most likely 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
✓
The hub router does not have a route to the spoke's LAN subnet.
In DMVPN phase 3, the hub must have 'ip nhrp redirect' enabled on the tunnel interface, and the spoke must have 'ip nhrp shortcut' enabled. Additionally, the hub must have a route to the spoke's subnet; otherwise, the hub will not send an NHRP redirect. The issue is that the hub does not have a route to the spoke's subnet.
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 does not have 'ip nhrp shortcut' enabled.
Why it's wrong here
Incorrect because the symptom is that the hub does not send the redirect; the spoke's shortcut setting does not affect the hub's redirect behavior.
- ✓
The hub router does not have a route to the spoke's LAN subnet.
Why this is correct
Correct because the hub must have a route to the spoke's subnet to generate an NHRP redirect; without it, the hub forwards traffic without sending a redirect.
- ✗
The tunnel interface on the hub has 'no ip nhrp redirect' configured.
Why it's wrong here
The question states the hub's NHRP configuration *includes* 'ip nhrp redirect', implying it is enabled. If 'no ip nhrp redirect' were configured on the tunnel interface, the hub would not be configured for redirects, directly contradicting the scenario where the command is present. This option is tempting because `no ip nhrp redirect` would indeed prevent redirects from being sent from that interface. It would be the correct choice if the hub was globally configured for redirect, but a specific interface was intended to *override* this behaviour and prevent redirects from being sent on that particular tunnel.
- ✗
The spoke's NHRP registration does not include the LAN subnet.
Why it's wrong here
Incorrect because NHRP registration includes the tunnel IP, not the LAN subnet; the hub learns the LAN subnet via routing protocols.
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Introduction to ENARSI Exam and Network Fundamentals
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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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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