hardMultiple ChoiceObjective-mapped
300-410 Practice Question: An engineer configures a DMVPN Phase 2 network
An engineer configures a DMVPN Phase 2 network. Spoke-to-spoke tunnels are established, but traffic between spokes is not being forwarded directly; it is still going through the hub. The engineer verifies that NHRP is working and spoke-to-spoke registrations are successful. What 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 is not sending NHRP redirect messages to the spokes.
In DMVPN Phase 2, spoke-to-spoke traffic requires that the spoke routers have a route to the destination prefix via the tunnel interface with the next-hop being the remote spoke's tunnel IP. If the hub is not configured to send an NHRP redirect or if the spoke does not have a route for the remote subnet via the tunnel, traffic will continue to go through the hub. The edge case is that the hub may be using a different next-hop in its routing table, or the spoke's routing table does not have a more specific route for the remote spoke's subnet via the 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 hub is not sending NHRP redirect messages to the spokes.
Why this is correct
In DMVPN Phase 2, the hub must send NHRP redirect messages to inform spokes of the existence of a direct path. Without these redirects, spokes do not know to send traffic directly to each other.
- ✗
The spoke routers have 'ip nhrp shortcut' disabled.
Why it's wrong here
The 'ip nhrp shortcut' command is used in Phase 3 to allow spoke-to-spoke tunnels; in Phase 2, it is not required as spokes can learn from NHRP redirects.
- ✗
The hub is configured with 'no ip split-horizon' on the tunnel interface.
Why it's wrong here
In DMVPN Phase 2, split horizon must be disabled on the hub to allow spoke-to-spoke traffic; if it is enabled, the hub will not advertise routes from one spoke to another, preventing direct communication.
- ✗
The spoke routers have mismatched IPsec transform sets.
Why it's wrong here
Mismatched IPsec transform sets would prevent the spoke-to-spoke tunnel from forming, but the question states spoke-to-spoke tunnels are established.
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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
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