- A
The hub's EIGRP is not configured to advertise the LAN subnet.
Why wrong: Incorrect. The stem explicitly states that spokes are learning the hub's LAN route, meaning EIGRP is advertising the LAN subnet.
- B
The spoke's tunnel interface has 'ip nhrp shortcut' disabled.
Why wrong: Incorrect. The 'ip nhrp shortcut' setting on the spoke is used for spoke-to-spoke shortcuts and does not affect spoke-to-hub reachability.
- C
The hub's tunnel interface has 'no ip nhrp redirect' configured.
Why wrong: Incorrect. The stem confirms that the hub's tunnel interface has 'ip nhrp redirect' enabled.
- D
The spoke's NHRP registration is not reaching the hub.
Correct. Without the spoke's NHRP registration, the hub lacks a mapping for the spoke's tunnel IP and cannot return traffic, causing ping failures.
DMVPN Phase 3 Hub LAN Not Advertised via EIGRP
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. A key principle to apply: dMVPN Phase 3. 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 is troubleshooting a DMVPN phase 3 network where spokes are unable to reach the hub's LAN subnet. The hub router is running EIGRP over the DMVPN tunnel interface, and the spokes are learning the hub's LAN route. However, pings from a spoke to the hub's LAN IP fail. The engineer checks the hub's routing table and sees the spoke's LAN route. The hub's tunnel interface has 'ip nhrp redirect' and 'ip nhrp shortcut' enabled. 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.
Quick Answer
The answer is that the hub’s EIGRP is not configured to advertise the LAN subnet. In a DMVPN Phase 3 network, the hub uses NHRP redirect and shortcut to dynamically direct spoke-to-spoke traffic, but the hub’s own LAN subnet must still be explicitly injected into EIGRP for spokes to learn a valid route to it. Without a network statement or a redistribute command covering the hub’s LAN interface, EIGRP will not advertise that subnet across the tunnel, leaving spokes with no path to reach it even though the hub may have routes for spoke LANs. This scenario directly tests your understanding of EIGRP route advertisement boundaries in DMVPN Phase 3 on the Cisco CCNP ENARSI 300-410 exam, where a common trap is assuming that NHRP redirect alone handles all routing. A quick memory tip: “If the hub’s LAN is not in EIGRP, the spokes can’t reach it—NHRP shortcuts only redirect traffic, they don’t originate routes.”
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 spoke's NHRP registration is not reaching the hub.
The spoke learns the hub's LAN route via EIGRP, but the hub lacks an NHRP mapping for the spoke's tunnel IP because the spoke's NHRP registration is not reaching the hub. When the spoke pings the hub's LAN IP, the hub receives the packet but cannot send a reply back to the spoke's tunnel IP, causing the ping to fail.
Key principle: DMVPN Phase 3
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's EIGRP is not configured to advertise the LAN subnet.
Why it's wrong here
Incorrect. The stem explicitly states that spokes are learning the hub's LAN route, meaning EIGRP is advertising the LAN subnet.
- ✗
The spoke's tunnel interface has 'ip nhrp shortcut' disabled.
Why it's wrong here
Incorrect. The 'ip nhrp shortcut' setting on the spoke is used for spoke-to-spoke shortcuts and does not affect spoke-to-hub reachability.
- ✗
The hub's tunnel interface has 'no ip nhrp redirect' configured.
Why it's wrong here
Incorrect. The stem confirms that the hub's tunnel interface has 'ip nhrp redirect' enabled.
- ✓
The spoke's NHRP registration is not reaching the hub.
Why this is correct
Correct. Without the spoke's NHRP registration, the hub lacks a mapping for the spoke's tunnel IP and cannot return traffic, causing ping failures.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
DMVPN Phase 3
Common exam traps
Common exam trap: answer the scenario, not the keyword
A common trap is to assume that routing is sufficient and overlook the need for NHRP registration for return traffic. Even with correct routing, without NHRP mapping, the hub cannot forward packets back to the spoke.
Detailed technical explanation
How to think about this question
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- DMVPN Phase 3
- NHRP Registration
- EIGRP over Tunnel
- Return Traffic Failure
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
DMVPN Phase 3
Real-world example
How this comes up in practice
A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
Visual reference
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
What to study next
Got this wrong? Here's your next step.
Review dMVPN Phase 3, then practise related 300-410 questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this 300-410 question test?
DMVPN — This question tests DMVPN — DMVPN Phase 3.
What is the correct answer to this question?
The correct answer is: The spoke's NHRP registration is not reaching the hub. — The spoke learns the hub's LAN route via EIGRP, but the hub lacks an NHRP mapping for the spoke's tunnel IP because the spoke's NHRP registration is not reaching the hub. When the spoke pings the hub's LAN IP, the hub receives the packet but cannot send a reply back to the spoke's tunnel IP, causing the ping to fail.
What should I do if I get this 300-410 question wrong?
Review dMVPN Phase 3, then practise related 300-410 questions on the same topic to reinforce the concept.
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?
DMVPN Phase 3
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Last reviewed: Jun 18, 2026
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