Question 740 of 2,152

DMVPN →mediumMultiple ChoiceObjective-mapped

Missing 'ip nhrp map multicast dynamic' on DMVPN Spoke

This 300-410 practice question tests your understanding of dmvpn. 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.

A spoke router has the following DMVPN configuration:

interface Tunnel0
 ip address 10.0.0.2 255.255.255.0
 ip nhrp network-id 100
 ip nhrp nhs 10.0.0.1

tunnel source GigabitEthernet0/0 tunnel mode gre multipoint

ip nhrp map 10.0.0.1 192.168.1.1

What is missing from this configuration?

A
The spoke is missing the 'ip nhrp map multicast dynamic' command to register with the hub.
Why wrong: The 'ip nhrp map multicast dynamic' command is typically used on the hub, not the spoke, and is not required for registration. The spoke's NHRP registration works via unicast using the 'ip nhrp nhs' and static mapping, so this is not missing.
B
The spoke is missing the 'ip nhrp authentication' command.
Why wrong: The 'ip nhrp authentication' command is optional and not required for basic DMVPN operation. Authentication can be added for security but is not missing in this configuration.
C
The spoke is missing the 'tunnel key' command.
The 'tunnel key' command is missing. In DMVPN, the hub often uses a tunnel key to identify the mGRE tunnel. Without matching tunnel key on the spoke, the tunnel might not come up properly. This is a common requirement in production environments.
D
The spoke is missing the 'ip nhrp holdtime' command.
Why wrong: The 'ip nhrp holdtime' command is optional; the default holdtime of 3600 seconds is sufficient for normal operation. It is not missing.

Full breakdown with real-world context →

Quick Answer

The answer is that the spoke is missing the 'ip nhrp map multicast dynamic' command. This command is essential because, in a DMVPN Phase 2 or Phase 3 network, the spoke must dynamically register its real interface (the tunnel source) with the hub NHS (10.0.0.1). Without it, the spoke cannot send NHRP registration packets to the hub, nor can it receive multicast or broadcast traffic—such as routing protocol hellos or dynamic routing updates—from the hub over the mGRE tunnel. On the Cisco CCNP ENARSI 300-410 exam, this is a classic configuration gap that tests your understanding of NHRP registration mechanics; a common trap is to assume that a static 'ip nhrp map' for the NHS alone is sufficient. Remember the memory tip: "No multicast dynamic, no registration—your spoke stays silent."

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 is missing the 'tunnel key' command.

The spoke configuration is missing the 'tunnel key' command, which is required in many DMVPN deployments when the hub is configured with a tunnel key. The tunnel key ensures that the mGRE interface on the spoke only accepts packets with the correct key, preventing misconfiguration. The existing commands 'ip nhrp nhs' and 'ip nhrp map' are sufficient for NHRP registration and unicast communication, but without a matching tunnel key, the spoke may not establish the tunnel correctly with the hub.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

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 is missing the 'ip nhrp map multicast dynamic' command to register with the hub.
Why it's wrong here
The 'ip nhrp map multicast dynamic' command is typically used on the hub, not the spoke, and is not required for registration. The spoke's NHRP registration works via unicast using the 'ip nhrp nhs' and static mapping, so this is not missing.
✗
The spoke is missing the 'ip nhrp authentication' command.
Why it's wrong here
The 'ip nhrp authentication' command is optional and not required for basic DMVPN operation. Authentication can be added for security but is not missing in this configuration.
✓
The spoke is missing the 'tunnel key' command.
Why this is correct
The 'tunnel key' command is missing. In DMVPN, the hub often uses a tunnel key to identify the mGRE tunnel. Without matching tunnel key on the spoke, the tunnel might not come up properly. This is a common requirement in production environments.
Related concept
Read the scenario before looking for a memorised answer.
✗
The spoke is missing the 'ip nhrp holdtime' command.
Why it's wrong here
The 'ip nhrp holdtime' command is optional; the default holdtime of 3600 seconds is sufficient for normal operation. It is not missing.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.

Trap categories for this question

Command / output trap
The 'ip nhrp map multicast dynamic' command is typically used on the hub, not the spoke, and is not required for registration. The spoke's NHRP registration works via unicast using the 'ip nhrp nhs' and static mapping, so this is not missing.

Detailed technical explanation

How to think about this question

This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.

KKey Concepts to Remember

Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
Use explanations to understand the rule behind the answer.

TExam Day Tips

Underline the problem statement mentally.
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

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

A practitioner preparing for the 300-410 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.

What to study next

Got this wrong? Here's your next step.

Identify which 300-410 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.

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FAQ

Questions learners often ask

What does this 300-410 question test?

DMVPN — This question tests DMVPN — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The spoke is missing the 'tunnel key' command. — The spoke configuration is missing the 'tunnel key' command, which is required in many DMVPN deployments when the hub is configured with a tunnel key. The tunnel key ensures that the mGRE interface on the spoke only accepts packets with the correct key, preventing misconfiguration. The existing commands 'ip nhrp nhs' and 'ip nhrp map' are sufficient for NHRP registration and unicast communication, but without a matching tunnel key, the spoke may not establish the tunnel correctly with the hub.

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

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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