The answer is that the CoPP policy is dropping incoming ICMP echo requests because the police rate is too low. CoPP (Control Plane Policing) applies only to traffic destined for the router’s control plane, such as incoming ping requests; when the rate is set to only 5000 bps, it is insufficient to handle the burst of ICMP packets, causing the router to drop them silently and fail to respond. This scenario tests your understanding that CoPP is unidirectional—it polices inbound control plane traffic only, so the router can still originate pings since outgoing ICMP is not affected. On the Cisco CCNP ENARSI 300-410 exam, this is a classic trap where candidates confuse the direction of CoPP enforcement or assume the policy applies symmetrically. A reliable memory tip: “CoPP cops the incoming, not the outgoing”—if the router can ping out but not answer pings in, the police rate is starving the control plane.
300-410 Control Plane Policing (CoPP) Practice Question
This 300-410 practice question tests your understanding of control plane policing (copp). 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 CoPP on a router to limit ICMP traffic to 5000 bps. After the policy is applied, the engineer notices that the router is not responding to ping requests from a remote network. However, the router can ping other devices successfully. The engineer checks the CoPP statistics and sees that the ICMP class has dropped packets. What is the most likely root cause?
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 CoPP policy is dropping incoming ICMP echo requests because the police rate is too low.
The CoPP policy is rate-limiting ICMP traffic to 5000 bps. Ping requests from the remote network are ICMP echo requests, which are processed by the control plane. If the rate is too low, these packets are dropped, causing the router to not respond to pings. The router can still originate pings because outgoing ICMP traffic is not subject to CoPP (CoPP applies to incoming control plane traffic).
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 is dropping incoming ICMP echo requests because the police rate is too low.
Why this is correct
Incoming ICMP packets are policed by CoPP, and if the rate is exceeded, they are dropped, preventing the router from responding.
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 CoPP policy is dropping outgoing ICMP echo replies because the police rate applies to both directions.
Why it's wrong here
CoPP applies to incoming traffic to the control plane, not outgoing traffic.
✗
The router's interface ACL is blocking incoming ICMP traffic.
Why it's wrong here
The scenario does not mention an ACL; CoPP is the likely cause.
✗
The router's ICMP rate-limit feature is enabled globally.
Why it's wrong here
ICMP rate-limit is a separate feature; the scenario focuses on CoPP.
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
The scenario does not mention an ACL; CoPP is the likely cause.
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.
Control Plane Policing (CoPP) — This question tests Control Plane Policing (CoPP) — 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 is dropping incoming ICMP echo requests because the police rate is too low. — The CoPP policy is rate-limiting ICMP traffic to 5000 bps. Ping requests from the remote network are ICMP echo requests, which are processed by the control plane. If the rate is too low, these packets are dropped, causing the router to not respond to pings. The router can still originate pings because outgoing ICMP traffic is not subject to CoPP (CoPP applies to incoming control plane traffic).
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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