The answer is that the hub is configured with 'ip nhrp redirect' but the spokes are missing 'ip nhrp shortcut'. In DMVPN Phase 2, spoke-to-spoke traffic relies on the hub sending NHRP redirect messages to inform a spoke that a better path exists directly to another spoke, and the receiving spoke must have the 'ip nhrp shortcut' command enabled to dynamically install that direct tunnel. Without the shortcut on the spokes, they ignore the redirect, so they never learn each other’s NBMA addresses and continue forwarding traffic through the hub, which explains why 'show dmvpn' only shows the hub. This scenario directly tests your understanding of the NHRP redirect/shortcut mechanism, a frequent trap on the Cisco CCNP ENARSI 300-410 exam where candidates mistakenly focus on tunnel mode or authentication. Remember the mnemonic: "The hub redirects, the spoke shortcuts"—both must be present for Phase 2 spoke-to-spoke to work.
300-410 Route Redistribution Practice Question
This 300-410 practice question tests your understanding of route redistribution. 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 configures DMVPN Phase 2 with NHRP. Spoke routers can communicate with the hub, but spoke-to-spoke traffic fails. The 'show dmvpn' on spokes shows the hub's NBMA address but not other spokes. 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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The hub is configured with 'ip nhrp redirect' but spokes are missing 'ip nhrp shortcut'.
In DMVPN Phase 2, spoke-to-spoke tunnels require NHRP redirect from the hub and NHRP shortcut on spokes. If the hub is not sending NHRP redirect messages (e.g., due to 'no ip nhrp redirect'), spokes will not learn each other's NBMA addresses, and traffic will be sent through the hub.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 configured with 'ip nhrp redirect' but spokes are missing 'ip nhrp shortcut'.
Why this is correct
Without 'ip nhrp shortcut' on spokes, they will not install dynamic NHRP entries.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
The tunnel interface mode is GRE IP, not mGRE.
Why it's wrong here
DMVPN uses mGRE; GRE IP would prevent multiple destinations.
✗
The spokes have different IPsec transform sets configured.
Why it's wrong here
IPsec mismatch would prevent tunnel establishment entirely.
✗
The NHRP authentication string is missing on the hub.
Why it's wrong here
NHRP auth mismatch would prevent registration, not spoke-to-spoke after registration.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 300-410 NAT questions on configuration and troubleshooting.
Route Redistribution — This question tests Route Redistribution — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The hub is configured with 'ip nhrp redirect' but spokes are missing 'ip nhrp shortcut'. — In DMVPN Phase 2, spoke-to-spoke tunnels require NHRP redirect from the hub and NHRP shortcut on spokes. If the hub is not sending NHRP redirect messages (e.g., due to 'no ip nhrp redirect'), spokes will not learn each other's NBMA addresses, and traffic will be sent through the hub.
What should I do if I get this 300-410 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 300-410 NAT questions on configuration and troubleshooting.
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?
Static NAT maps one inside address to one outside address.
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