- 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.
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.”
300-410 DMVPN Practice Question
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.
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: 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 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
Static NAT maps one inside address to one outside address.
- ✗
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: 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.
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?
DMVPN — This question tests DMVPN — Static NAT maps one inside address to one outside address..
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?
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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Last reviewed: Jun 18, 2026
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