- A
The hub is not configured with 'ip nhrp redirect' and the spokes are not configured with 'ip nhrp shortcut'.
In Phase 2, the hub must send NHRP redirect messages to trigger the spoke to send a resolution request. Without these commands, spokes will not attempt to build a direct tunnel.
- B
The spokes have different NHRP authentication strings, causing NHRP resolution to fail.
Why wrong: If authentication were mismatched, NHRP registration would fail, but the problem states registration is successful.
- C
The tunnel interface on the spokes is configured with 'tunnel mode gre multipoint' but the hub uses 'tunnel mode gre ip'.
Why wrong: In Phase 2, the hub must use multipoint GRE (mGRE), but the spokes can use either. This mismatch would prevent the hub from accepting multiple connections, but not spoke-to-spoke.
- D
The spokes are using different IPsec transform sets, causing the IPsec tunnel to fail.
Why wrong: IPsec transform sets are negotiated between peers. If they mismatch, the IPsec tunnel would not form, but the issue is with NHRP triggering the tunnel.
300-410 Device Access Control Practice Question
This 300-410 practice question tests your understanding of device access control. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
An engineer configures DMVPN Phase 2 with spoke-to-spoke tunnels. Spokes can ping each other's physical interfaces, but cannot establish a direct tunnel. NHRP registration is successful. Which is the most likely explanation?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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 configured with 'ip nhrp redirect' and the spokes are not configured with 'ip nhrp shortcut'.
In DMVPN Phase 2, spoke-to-spoke tunnels require NHRP redirect and shortcut mechanisms to dynamically build direct tunnels. The hub must be configured with 'ip nhrp redirect' to send redirect messages to spokes, and spokes must have 'ip nhrp shortcut' to install the NHRP-learned /32 host routes for direct traffic. Without these, spokes will forward traffic through the hub even though they can ping each other's physical interfaces, preventing the establishment of a direct tunnel.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 configured with 'ip nhrp redirect' and the spokes are not configured with 'ip nhrp shortcut'.
Why this is correct
In Phase 2, the hub must send NHRP redirect messages to trigger the spoke to send a resolution request. Without these commands, spokes will not attempt to build a direct tunnel.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The spokes have different NHRP authentication strings, causing NHRP resolution to fail.
Why it's wrong here
If authentication were mismatched, NHRP registration would fail, but the problem states registration is successful.
- ✗
The tunnel interface on the spokes is configured with 'tunnel mode gre multipoint' but the hub uses 'tunnel mode gre ip'.
Why it's wrong here
In Phase 2, the hub must use multipoint GRE (mGRE), but the spokes can use either. This mismatch would prevent the hub from accepting multiple connections, but not spoke-to-spoke.
- ✗
The spokes are using different IPsec transform sets, causing the IPsec tunnel to fail.
Why it's wrong here
IPsec transform sets are negotiated between peers. If they mismatch, the IPsec tunnel would not form, but the issue is with NHRP triggering the tunnel.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that successful NHRP registration alone guarantees spoke-to-spoke tunnels, when in fact the redirect and shortcut commands are mandatory for Phase 2 dynamic tunnel establishment.
Detailed technical explanation
How to think about this question
The NHRP redirect mechanism leverages the hub's routing table to detect suboptimal paths; when a spoke sends traffic to another spoke via the hub, the hub sends an NHRP Redirect message to the source spoke, which then triggers an NHRP Resolution Request to the destination spoke. The 'ip nhrp shortcut' command on the spoke installs a /32 host route pointing to the destination spoke's tunnel IP, enabling direct forwarding. This behavior is defined in RFC 2332 and is critical for scaling DMVPN networks by offloading traffic from the hub.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Questions learners often ask
What does this 300-410 question test?
Device Access Control — This question tests Device Access Control — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The hub is not configured with 'ip nhrp redirect' and the spokes are not configured with 'ip nhrp shortcut'. — In DMVPN Phase 2, spoke-to-spoke tunnels require NHRP redirect and shortcut mechanisms to dynamically build direct tunnels. The hub must be configured with 'ip nhrp redirect' to send redirect messages to spokes, and spokes must have 'ip nhrp shortcut' to install the NHRP-learned /32 host routes for direct traffic. Without these, spokes will forward traffic through the hub even though they can ping each other's physical interfaces, preventing the establishment of a direct tunnel.
What should I do if I get this 300-410 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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