Question 1,870 of 2,152

Device Management →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is that the spoke routers lack a route to each other's tunnel IP via the hub, which prevents the NHRP shortcut from being triggered. In DMVPN Phase 2, spoke-to-spoke tunnels rely on the NHRP redirect and shortcut mechanism, but this process only initiates when a spoke has a valid route in its routing table pointing to the remote spoke’s tunnel address through the hub. Without that specific route, the spoke cannot send the initial data packet to the hub for redirection, so the shortcut request never fires. On the Cisco CCNP ENARSI 300-410 exam, this concept tests your understanding of how Phase 2 differs from Phase 1 and Phase 3—the common trap is assuming that successful NHRP registration alone guarantees spoke-to-spoke connectivity. Remember the memory tip: “No route via hub, no shortcut—Phase 2 needs a path through the hub to kickstart the spoke-to-spoke tunnel.”

300-410 Device Management Practice Question

This 300-410 practice question tests your understanding of device management. 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 do not form, even though 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.

Question 1hardmultiple choice

Read the full VPN explanation →

A
The spoke routers do not have a route to each other's tunnel IP via the hub, so the NHRP shortcut request fails.
Phase 2 requires that the spoke's routing table points to the hub for the remote spoke's tunnel IP; otherwise, the shortcut cannot be established.
B
The NHRP authentication key is mismatched between spokes.
Why wrong: NHRP authentication is between spoke and hub, not between spokes.
C
The mGRE interface is configured with tunnel mode gre multipoint on the spokes.
Why wrong: mGRE is required for Phase 2 and is correctly configured.
D
The hub is not configured with 'ip nhrp redirect' and the spokes with 'ip nhrp shortcut'.
Why wrong: These are required for Phase 2, but the scenario states registration is successful, implying these are configured.

Full breakdown with real-world context →

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 routers do not have a route to each other's tunnel IP via the hub, so the NHRP shortcut request fails.

In DMVPN Phase 2, spoke-to-spoke tunnels require that the spoke routers have a route to each other's tunnel IP via the hub. Phase 2 uses NHRP redirect and shortcut, but the spoke must have a route pointing to the hub for the destination network. If the spoke's routing table does not have a route to the remote spoke's tunnel IP via the hub, the shortcut will not be triggered.

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 do not have a route to each other's tunnel IP via the hub, so the NHRP shortcut request fails.
Why this is correct
Phase 2 requires that the spoke's routing table points to the hub for the remote spoke's tunnel IP; otherwise, the shortcut cannot be established.
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 NHRP authentication key is mismatched between spokes.
Why it's wrong here
NHRP authentication is between spoke and hub, not between spokes.
✗
The mGRE interface is configured with tunnel mode gre multipoint on the spokes.
Why it's wrong here
mGRE is required for Phase 2 and is correctly configured.
✗
The hub is not configured with 'ip nhrp redirect' and the spokes with 'ip nhrp shortcut'.
Why it's wrong here
These are required for Phase 2, but the scenario states registration is successful, implying these are configured.

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.

Trap categories for this question

Scenario analysis trap
These are required for Phase 2, but the scenario states registration is successful, implying these are configured.

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.

What to study next

Got this wrong? Here's your next step.

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.

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FAQ

Questions learners often ask

What does this 300-410 question test?

Device Management — This question tests Device Management — 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 do not have a route to each other's tunnel IP via the hub, so the NHRP shortcut request fails. — In DMVPN Phase 2, spoke-to-spoke tunnels require that the spoke routers have a route to each other's tunnel IP via the hub. Phase 2 uses NHRP redirect and shortcut, but the spoke must have a route pointing to the hub for the destination network. If the spoke's routing table does not have a route to the remote spoke's tunnel IP via the hub, the shortcut will not be triggered.

What should I do if I get this 300-410 question wrong?

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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