- A
Add 'permit icmp any any' to access-list 150 to include ICMP in the COPP-CORE class.
Correct. Adding ICMP to the ACL would match it in the COPP-CORE class and apply the lower 64000 bps policer, providing better protection.
- B
Change the class-default police rate to 64000 bps to match the COPP-CORE rate.
Why wrong: Incorrect. While that would lower the rate for ICMP, it would also affect all other unclassified traffic. Better to specifically classify ICMP.
- C
Add a second class-map for ICMP and apply a separate policer.
Why wrong: Incorrect. That would work but is not the simplest fix. The question asks what is missing, and the simplest answer is to add ICMP to the existing ACL.
- D
The configuration is complete; ICMP is not a significant control-plane threat.
Why wrong: Incorrect. ICMP echo requests can be used for control-plane attacks, so they should be rate-limited.
Protecting Against ICMP Attacks with CoPP
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.
Consider the following CoPP configuration:
access-list 150 permit tcp any any eq 179 access-list 150 permit udp any any eq 646
! class-map match-all COPP-CORE match access-group 150 ! policy-map COPP-POLICY
class COPP-CORE
police 64000 conform-action transmit exceed-action drop
class class-default
police 128000 conform-action transmit exceed-action drop ! control-plane service-policy input COPP-POLICY
What is missing from this configuration to also protect against ICMP-based control-plane attacks?
Quick Answer
The answer is to add 'permit icmp any any' to access-list 150 so that ICMP traffic is matched by the COPP-CORE class. Without this entry, ICMP packets fall into the class-default, where they are policed at 128,000 bps—a rate that is often too generous to effectively mitigate a control-plane attack, such as a ping flood. On the Cisco CCNP ENARSI 300-410 exam, this question tests your understanding of how CoPP class-maps rely on ACLs to selectively police critical protocols; a common trap is assuming the default class provides adequate protection for all traffic types. The key insight is that CoPP works by explicitly classifying sensitive control-plane protocols—like BGP, LDP, and ICMP—into a higher-priority class with a lower police rate, while leaving less critical traffic in the default. A useful memory tip: "If it talks to the control plane, it needs its own ACL line—don't let ICMP fall through the default crack."
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
Add 'permit icmp any any' to access-list 150 to include ICMP in the COPP-CORE class.
Option A is correct because the current CoPP configuration only matches BGP (TCP port 179) and LDP (UDP port 646) traffic in the COPP-CORE class. ICMP-based control-plane attacks (e.g., ICMP floods, Smurf attacks) are not matched by any explicit class, so they fall into class-default, which has a higher police rate (128 kbps) and may allow excessive ICMP traffic to reach the control plane. Adding 'permit icmp any any' to access-list 150 ensures ICMP packets are classified into COPP-CORE and subjected to the more restrictive 64 kbps policer, protecting the control plane from ICMP-based attacks.
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.
- ✓
Add 'permit icmp any any' to access-list 150 to include ICMP in the COPP-CORE class.
- ✗
Change the class-default police rate to 64000 bps to match the COPP-CORE rate.
Why it's wrong here
Incorrect. While that would lower the rate for ICMP, it would also affect all other unclassified traffic. Better to specifically classify ICMP.
- ✗
Add a second class-map for ICMP and apply a separate policer.
- ✗
The configuration is complete; ICMP is not a significant control-plane threat.
Why it's wrong here
Incorrect. ICMP echo requests can be used for control-plane attacks, so they should be rate-limited.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that class-default alone is sufficient for all unmatched traffic, but the trap here is that ICMP is a direct control-plane threat that must be explicitly classified and rate-limited, not left to the default catch-all policer which may be too permissive.
Detailed technical explanation
How to think about this question
Under the hood, CoPP uses a hierarchical policing model where the control-plane service policy is applied to all packets destined to the router's control plane (e.g., routing protocols, management traffic, ICMP). The class-default policer acts as a catch-all, but its rate (128 kbps) is often too permissive for ICMP floods. In real-world deployments, ICMP rate-limiting is critical because ICMP packets are processed by the route processor's interrupt level, and a flood can cause CPU starvation. Cisco best practices (e.g., CoPP for IOS/IOS-XE) recommend matching ICMP types (echo, echo-reply, unreachable) with specific permit statements and applying a low policer rate (e.g., 32-64 kbps) to prevent DoS while allowing legitimate ICMP for path MTU discovery and diagnostics.
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.
TExam Day Tips
- 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 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.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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Control Plane Policing (CoPP) — study guide chapter
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FAQ
Questions learners often ask
What does this 300-410 question test?
Control Plane Policing (CoPP) — This question tests Control Plane Policing (CoPP) — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Add 'permit icmp any any' to access-list 150 to include ICMP in the COPP-CORE class. — Option A is correct because the current CoPP configuration only matches BGP (TCP port 179) and LDP (UDP port 646) traffic in the COPP-CORE class. ICMP-based control-plane attacks (e.g., ICMP floods, Smurf attacks) are not matched by any explicit class, so they fall into class-default, which has a higher police rate (128 kbps) and may allow excessive ICMP traffic to reach the control plane. Adding 'permit icmp any any' to access-list 150 ensures ICMP packets are classified into COPP-CORE and subjected to the more restrictive 64 kbps policer, protecting the control plane from ICMP-based attacks.
What should I do if I get this 300-410 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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