The answer is that the class-map CoPP-ICMP shows zero packets matched because the referenced access-list 100 does not account for all ICMP types the control plane actually receives. This occurs because the access-list only permits specific ICMP types—echo, echo-reply, time-exceeded, and unreachable—but the router’s control plane may be processing other ICMP types, such as parameter-problem or redirect, which are not listed and thus get dropped before the class-map can count them. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of how Control Plane Policing (CoPP) relies on precise ACL entries to classify traffic; a common trap is assuming a few common ICMP types are sufficient, when in reality the control plane often handles a broader set. Remember that CoPP class-map with zero matches usually points to an incomplete match criterion, not a misapplied policy. A useful memory tip is “ICMP types are like keys—missing one locks the door,” so always verify you’ve covered all types the router might need to police.
300-410 Control Plane Policing (CoPP) Practice Question
This 300-410 practice question tests your understanding of control plane policing (copp). The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 runs the following command on Router R1:
R1# show access-lists 100
Extended IP access list 100
10 permit icmp any any echo
20 permit icmp any any echo-reply
30 permit icmp any any time-exceeded
40 permit icmp any any unreachable
R1# show policy-map control-plane
Based on this output, what is the most likely problem?
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 access-list does not include all ICMP types that may be sent to the control plane.
The access-list 100 matches ICMP types, but the class-map CoPP-ICMP uses 'match-all' which requires all match criteria to be met. Since only one access-group is referenced, 'match-all' is not incorrect, but the access-list may not be matching the actual ICMP traffic types sent to the control plane (e.g., ICMP type 8 for echo, but the router may receive other types). However, the key issue is that the class-map is not matching any packets, likely because the access-list is incomplete or the traffic is not matching the specified ICMP types.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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 class-map uses 'match-all' instead of 'match-any'.
Why it's wrong here
With a single match criterion, 'match-all' and 'match-any' behave the same.
✓
The access-list does not include all ICMP types that may be sent to the control plane.
Why this is correct
The access-list only matches specific ICMP types, potentially missing others like router advertisement or parameter problem.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✗
The police rate is too low and is dropping all packets.
Why it's wrong here
The counters show 0 packets, so no packets have been classified to be dropped.
✗
The policy-map is applied to the wrong direction.
Why it's wrong here
The policy is applied to input, which is correct for CoPP.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Trap categories for this question
Command / output trap
The counters show 0 packets, so no packets have been classified to be dropped.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Real-world example
How this comes up in practice
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
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 ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related 300-410 ACL questions on filtering logic and placement.
Control Plane Policing (CoPP) — This question tests Control Plane Policing (CoPP) — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: The access-list does not include all ICMP types that may be sent to the control plane. — The access-list 100 matches ICMP types, but the class-map CoPP-ICMP uses 'match-all' which requires all match criteria to be met. Since only one access-group is referenced, 'match-all' is not incorrect, but the access-list may not be matching the actual ICMP traffic types sent to the control plane (e.g., ICMP type 8 for echo, but the router may receive other types). However, the key issue is that the class-map is not matching any packets, likely because the access-list is incomplete or the traffic is not matching the specified ICMP types.
What should I do if I get this 300-410 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related 300-410 ACL questions on filtering logic and placement.
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?
Standard ACLs match source addresses.
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