Question 1,075 of 2,152

DMVPN →hardMultiple ChoiceObjective-mapped

CoPP Dropping NHRP Registration Packets — Troubleshooting | Cisco CCNP ENARSI 300-410 Explained

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 network engineer configures Control Plane Policing (CoPP) on a DMVPN hub router to protect the control plane. The policy includes a class-map matching NHRP traffic and a police rate of 1000 pps. Unexpectedly, after applying the policy, NHRP registrations from spokes fail intermittently, and debug shows packets being dropped by CoPP. 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.

A
The CoPP policy's class-default has a lower police rate or is set to drop, and NHRP traffic is not explicitly matched in a higher class, causing it to fall into class-default and be dropped.
If NHRP traffic is not classified in a specific class, it matches class-default, which may have a restrictive policy, leading to drops.
B
The police rate of 1000 pps is too high for the hub's CPU, causing the router to drop packets due to CPU overload.
Why wrong: CoPP protects the CPU; a high rate would allow more traffic, not cause drops.
C
The CoPP policy is applied to the wrong interface; it should be applied to the tunnel interface, not the physical interface.
Why wrong: CoPP is applied globally to the control plane, not to interfaces; it filters traffic destined to the router itself.
D
The NHRP packets are being classified as 'critical' traffic, and the CoPP policy has a lower priority for critical traffic.
Why wrong: CoPP does not have priority levels; it uses class maps based on ACLs or DSCP.

Full breakdown with real-world context →

Quick Answer

The answer is that NHRP packets are being dropped because the CoPP policy’s class-default either has a lower police rate or is configured to drop, and the NHRP traffic is not explicitly matched in a higher-priority class. This occurs because CoPP applies a token-bucket policer to control-plane traffic; when NHRP registration packets from multiple DMVPN spokes arrive in bursts, they can exceed the policer’s committed rate or burst size if not properly classified. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of CoPP class-map ordering and the default behavior of class-default—a common trap where engineers assume all critical traffic is matched, but forget that unclassified traffic falls to the default class with potentially restrictive policing. Remember the memory tip: “If it’s not in a class, it’s in default—and default may default to drop.”

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 CoPP policy's class-default has a lower police rate or is set to drop, and NHRP traffic is not explicitly matched in a higher class, causing it to fall into class-default and be dropped.

CoPP rate-limits control plane traffic. If the police rate is set in packets per second (pps), but the actual NHRP registration traffic is bursty (e.g., multiple spokes registering simultaneously), the policer may drop packets. The corner case is that the default CoPP class-default may also match NHRP traffic if not explicitly classified, and the class-default may have a lower rate or be set to drop. Additionally, CoPP uses a token bucket; if the rate is too low or the burst size is insufficient, packets are dropped. The engineer should ensure that NHRP traffic is matched in a dedicated class with appropriate rate and burst.

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 CoPP policy's class-default has a lower police rate or is set to drop, and NHRP traffic is not explicitly matched in a higher class, causing it to fall into class-default and be dropped.
Why this is correct
If NHRP traffic is not classified in a specific class, it matches class-default, which may have a restrictive policy, leading to drops.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The police rate of 1000 pps is too high for the hub's CPU, causing the router to drop packets due to CPU overload.
Why it's wrong here
CoPP protects the CPU; a high rate would allow more traffic, not cause drops.
✗
The CoPP policy is applied to the wrong interface; it should be applied to the tunnel interface, not the physical interface.
Why it's wrong here
CoPP is applied globally to the control plane, not to interfaces; it filters traffic destined to the router itself.
✗
The NHRP packets are being classified as 'critical' traffic, and the CoPP policy has a lower priority for critical traffic.
Why it's wrong here
CoPP does not have priority levels; it uses class maps based on ACLs or DSCP.

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.

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 CoPP policy's class-default has a lower police rate or is set to drop, and NHRP traffic is not explicitly matched in a higher class, causing it to fall into class-default and be dropped. — CoPP rate-limits control plane traffic. If the police rate is set in packets per second (pps), but the actual NHRP registration traffic is bursty (e.g., multiple spokes registering simultaneously), the policer may drop packets. The corner case is that the default CoPP class-default may also match NHRP traffic if not explicitly classified, and the class-default may have a lower rate or be set to drop. Additionally, CoPP uses a token bucket; if the rate is too low or the burst size is insufficient, packets are dropped. The engineer should ensure that NHRP traffic is matched in a dedicated class with appropriate rate and burst.

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?

Read the scenario before looking for a memorised answer.

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