The answer is that the spoke’s tunnel interface is missing the 'ip nhrp shortcut' command. In DMVPN Phase 2, the 'ip nhrp redirect' on the hub and 'ip nhrp shortcut' on the spoke work together to trigger spoke-to-spoke tunnel establishment: when the hub forwards traffic between spokes, it sends an NHRP redirect message, and the spoke must have 'ip nhrp shortcut' enabled to act on that redirect by sending an NHRP resolution request to the destination spoke. Without this command, the spoke sees the route via the hub but never initiates the shortcut, even though the hub forwards traffic correctly. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of the DMVPN Phase 2 control-plane flow, where the spoke’s shortcut capability is the critical trigger—a common trap is assuming the route alone is sufficient. Memory tip: “No shortcut, no shortcut tunnel” — if the spoke lacks 'ip nhrp shortcut', it will never build a direct spoke-to-spoke path.
300-410 DMVPN Practice Question
This 300-410 practice question tests your understanding of dmvpn. 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.
A network engineer is troubleshooting a DMVPN phase 2 network where spoke-to-spoke tunnels are not being established. The hub router has 'ip nhrp redirect' enabled, and spokes have 'ip nhrp shortcut' enabled. The engineer notices that when a spoke sends traffic to another spoke, the hub forwards the traffic correctly, but the spoke does not initiate an NHRP resolution request to the destination spoke. The spoke's routing table shows the destination subnet via the hub. What is the most likely cause?
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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The spoke's tunnel interface does not have 'ip nhrp shortcut' enabled.
In DMVPN phase 2, spoke-to-spoke tunnels are triggered by the spoke sending an NHRP resolution request to the hub. The spoke will only send this request if it has a route to the destination subnet via the tunnel interface. If the spoke's routing table shows the route via the hub (next-hop is the hub's tunnel IP), the spoke should send a resolution request. However, if the spoke's 'ip nhrp shortcut' is not enabled, it will not attempt to create a shortcut. The issue is that 'ip nhrp shortcut' is missing on the spoke.
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.
✓
The spoke's tunnel interface does not have 'ip nhrp shortcut' enabled.
Why this is correct
Correct because 'ip nhrp shortcut' is required for the spoke to initiate NHRP resolution requests for spoke-to-spoke tunnels.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
The hub's tunnel interface does not have 'ip nhrp redirect' enabled.
Why it's wrong here
Incorrect because the engineer verified that 'ip nhrp redirect' is enabled on the hub.
✗
The spoke's routing table has a static route to the destination subnet via the hub.
Why it's wrong here
Incorrect because a static route would still allow the spoke to send a resolution request if shortcut is enabled.
✗
The hub's NHRP authentication is configured but the spoke's is not.
Why it's wrong here
Incorrect because NHRP authentication affects registration, not resolution requests.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
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.
DMVPN — This question tests DMVPN — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The spoke's tunnel interface does not have 'ip nhrp shortcut' enabled. — In DMVPN phase 2, spoke-to-spoke tunnels are triggered by the spoke sending an NHRP resolution request to the hub. The spoke will only send this request if it has a route to the destination subnet via the tunnel interface. If the spoke's routing table shows the route via the hub (next-hop is the hub's tunnel IP), the spoke should send a resolution request. However, if the spoke's 'ip nhrp shortcut' is not enabled, it will not attempt to create a shortcut. The issue is that 'ip nhrp shortcut' is missing on the spoke.
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.
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?
CIDR notation defines the prefix length.
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