- A
R1 (hub) does not have 'ip nhrp redirect' enabled on its tunnel interface, so it does not send redirect messages to R3, preventing direct spoke-to-spoke tunnel establishment.
Correct. In Phase 2, the hub must have NHRP redirect enabled to inform spokes of direct paths. Without it, spokes forward traffic through the hub.
- B
R2 has 'ip nhrp shortcut' disabled, preventing direct tunnel establishment.
Why wrong: Incorrect. 'ip nhrp shortcut' is used on spokes to accept redirects, but the issue is that redirects are not being sent.
- C
R3 has a static route pointing to R1 for the subnet behind R2.
Why wrong: Incorrect. Static routes could cause this, but the question focuses on NHRP configuration.
- D
EIGRP is not redistributing the subnet behind R2 to R3.
Why wrong: Incorrect. If R3 can ping R2's tunnel IP, routing is working. The issue is path selection.
Quick Answer
The answer is that the hub router R1 is missing the 'ip nhrp redirect' command on its tunnel interface. In DMVPN Phase 2, direct spoke-to-spoke tunnels rely on the hub sending NHRP redirect messages to inform a spoke that a better path exists to another spoke; without this command on the hub, R3 never receives a redirect when it sends traffic for R2’s subnet, so it continues forwarding through the hub instead of building a direct tunnel. This question tests your understanding of the NHRP redirect mechanism and its dependency on the hub, a common pitfall in the Cisco CCNP ENARSI 300-410 exam where candidates often assume only the spoke needs the redirect command. A frequent trap is confusing Phase 2 with Phase 3—remember that in Phase 2, the hub initiates the redirect, while the spoke only needs 'ip nhrp shortcut' to accept it. Memory tip: "Redirect is a hub job; without it, spokes stay stuck through the hub."
300-410 DMVPN Practice Question
This 300-410 practice question tests your understanding of dmvpn. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
In a DMVPN Phase 2 network with EIGRP, R1 (hub) and R2 (spoke) are configured. R2's tunnel interface has 'ip nhrp redirect' enabled. R3 (another spoke) can ping R2's tunnel IP, but when R3 tries to reach a subnet behind R2, traffic is forwarded to R1 instead of directly to R2. What is the root 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
R1 (hub) does not have 'ip nhrp redirect' enabled on its tunnel interface, so it does not send redirect messages to R3, preventing direct spoke-to-spoke tunnel establishment.
In DMVPN Phase 2, spoke-to-spoke tunnels are established using NHRP redirect. However, if the hub does not have 'ip nhrp redirect' enabled, it will not send redirect messages to spokes. Without redirect, spokes will not learn the direct path to other spokes and will forward traffic through the hub.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
R1 (hub) does not have 'ip nhrp redirect' enabled on its tunnel interface, so it does not send redirect messages to R3, preventing direct spoke-to-spoke tunnel establishment.
Why this is correct
Correct. In Phase 2, the hub must have NHRP redirect enabled to inform spokes of direct paths. Without it, spokes forward traffic through the hub.
Related concept
CIDR notation defines the prefix length.
- ✗
R2 has 'ip nhrp shortcut' disabled, preventing direct tunnel establishment.
Why it's wrong here
Incorrect. 'ip nhrp shortcut' is used on spokes to accept redirects, but the issue is that redirects are not being sent.
- ✗
R3 has a static route pointing to R1 for the subnet behind R2.
Why it's wrong here
Incorrect. Static routes could cause this, but the question focuses on NHRP configuration.
- ✗
EIGRP is not redistributing the subnet behind R2 to R3.
Why it's wrong here
Incorrect. If R3 can ping R2's tunnel IP, routing is working. The issue is path selection.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
- CIDR notation defines the prefix length.
- Block size helps identify subnet boundaries.
- Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
- The required host count determines the smallest suitable subnet.
TExam Day Tips
- Write the block size before choosing the subnet.
- Check whether the question asks for hosts, subnets or a specific address range.
- Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 300-410 subnetting questions on CIDR, address ranges, and subnet selection.
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FAQ
Questions learners often ask
What does this 300-410 question test?
DMVPN — This question tests DMVPN — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: R1 (hub) does not have 'ip nhrp redirect' enabled on its tunnel interface, so it does not send redirect messages to R3, preventing direct spoke-to-spoke tunnel establishment. — In DMVPN Phase 2, spoke-to-spoke tunnels are established using NHRP redirect. However, if the hub does not have 'ip nhrp redirect' enabled, it will not send redirect messages to spokes. Without redirect, spokes will not learn the direct path to other spokes and will forward traffic through the hub.
What should I do if I get this 300-410 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 300-410 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Last reviewed: Jun 18, 2026
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