The answer is that the spoke routers have a default route via the hub, which prevents them from using the direct tunnel. In DMVPN Phase 2, spoke-to-spoke traffic requires the spoke to have a specific route to the destination network via the tunnel interface, with a next hop that triggers NHRP resolution for a direct path. When a default route points to the hub, the spoke forwards all non-local traffic to the hub instead of initiating the NHRP resolution process, so the direct tunnel remains unused. On the Cisco CCNP ENARSI 300-410 exam, this tests your understanding of how routing and NHRP interact in Phase 2; a common trap is assuming that establishing the mGRE tunnel automatically enables spoke-to-spoke traffic. Remember the key condition: for a direct tunnel to form, the spoke must have a route with a next hop that is not the hub. Memory tip: “No default, no hub—direct spoke-to-spoke needs a specific route to the sub.”
300-410 BGP Troubleshooting Practice Question
This 300-410 practice question tests your understanding of bgp troubleshooting. 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.
An engineer configures a DMVPN Phase 2 network. Spoke-to-spoke tunnels are established, but traffic between spokes is not using the direct tunnel. What 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 spoke routers have a default route via the hub, so they send traffic to the hub instead of initiating NHRP resolution for a direct tunnel.
In DMVPN Phase 2, spoke-to-spoke tunnels require that the spoke routers have a route to the destination network via the tunnel interface with a next hop that triggers NHRP resolution. If the spoke has a default route pointing to the hub, it will not attempt to resolve the spoke-to-spoke tunnel.
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 spoke routers have a default route via the hub, so they send traffic to the hub instead of initiating NHRP resolution for a direct tunnel.
Why this is correct
Phase 2 requires that spokes have a specific route to the remote subnet to trigger NHRP; a default route prevents this.
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 hub has 'no ip nhrp redirect' configured, which disables spoke-to-spoke tunnel setup.
Why it's wrong here
In Phase 2, the hub does not send redirect messages; that is Phase 3.
✗
The spokes have 'ip nhrp shortcut' enabled, which forces all traffic through the hub.
Why it's wrong here
Shortcut is used in Phase 3, not Phase 2.
✗
The tunnel mode is set to 'tunnel mode gre multipoint' on the spokes, which is incorrect.
Why it's wrong here
Spokes can use point-to-point GRE in Phase 2, but multipoint is also valid.
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.
BGP Troubleshooting — This question tests BGP Troubleshooting — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The spoke routers have a default route via the hub, so they send traffic to the hub instead of initiating NHRP resolution for a direct tunnel. — In DMVPN Phase 2, spoke-to-spoke tunnels require that the spoke routers have a route to the destination network via the tunnel interface with a next hop that triggers NHRP resolution. If the spoke has a default route pointing to the hub, it will not attempt to resolve the spoke-to-spoke tunnel.
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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