Question 29 of 2,015

ACLs and CoPP →mediumMultiple ChoiceObjective-mapped

Quick Answer

The answer is that the CoPP policy is policing ICMP traffic to a rate that is too low for the monitoring server's traffic. Control Plane Policing (CoPP) protects the switch CPU by rate-limiting certain types of traffic, and when ICMP echo requests from a monitoring server exceed the configured police rate, legitimate packets are dropped even though the server is a valid source. On the ENCOR 350-401 exam, this scenario tests your understanding that CoPP drops are not always due to an attack—they can simply result from misconfigured rate limits that fail to accommodate normal monitoring traffic. A common trap is to blame the monitoring server or assume a CPU overload, but the CoPP statistics showing drops specifically for matched ICMP traffic point directly to policing thresholds. Remember the memory tip: “CoPP drops don’t mean attack—check the rate, not the source.”

350-401 ACLs and CoPP Practice Question

This 350-401 practice question tests your understanding of acls and 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.

An enterprise network uses a Cisco Catalyst 9300 switch as a distribution layer device. The network team notices that ICMP echo requests from a monitoring server (192.168.1.100) to the switch's management IP are being dropped intermittently. The switch has a CoPP policy that includes a class-map matching ICMP traffic. The engineer checks the CoPP statistics and sees that ICMP packets from the monitoring server are being dropped by the policy. What is the most likely cause of this issue?

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.

Question 1mediummultiple choice

Study the full ACL explanation →

A
The CoPP policy is policing ICMP traffic to a rate that is too low for the monitoring server's traffic.
Correct because CoPP polices traffic to the control plane; if the rate is too low, legitimate ICMP packets may be dropped.
B
An ACL applied to the management interface is blocking ICMP from the monitoring server.
Why wrong: Incorrect because the CoPP statistics show drops due to the policy, not an interface ACL.
C
The monitoring server is sending ICMP packets with a TTL of 1, causing them to be dropped.
Why wrong: Incorrect because TTL=1 would cause packets to be dropped before reaching the switch, not due to CoPP.
D
The switch's CPU is overloaded, causing CoPP to drop all packets.
Why wrong: Incorrect because CoPP drops are based on policy, not CPU load; CPU overload might cause other issues but not CoPP drops specifically.

Full breakdown with real-world context →

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 is policing ICMP traffic to a rate that is too low for the monitoring server's traffic.

The correct answer is that the CoPP policy is policing ICMP traffic to a rate that is too low for the monitoring server's traffic. Option B is incorrect because the ACL is not mentioned as blocking ICMP. Option C is incorrect because the monitoring server is not the source of the issue; it is the target. Option D is incorrect because the switch's CPU is not necessarily overloaded; the drops are due to CoPP policing.

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 CoPP policy is policing ICMP traffic to a rate that is too low for the monitoring server's traffic.
Why this is correct
Correct because CoPP polices traffic to the control plane; if the rate is too low, legitimate ICMP packets may be dropped.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✗
An ACL applied to the management interface is blocking ICMP from the monitoring server.
Why it's wrong here
Incorrect because the CoPP statistics show drops due to the policy, not an interface ACL.
✗
The monitoring server is sending ICMP packets with a TTL of 1, causing them to be dropped.
Why it's wrong here
Incorrect because TTL=1 would cause packets to be dropped before reaching the switch, not due to CoPP.
✗
The switch's CPU is overloaded, causing CoPP to drop all packets.
Why it's wrong here
Incorrect because CoPP drops are based on policy, not CPU load; CPU overload might cause other issues but not CoPP drops specifically.

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
Incorrect because the CoPP statistics show drops due to the policy, not an interface ACL.

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.

What to study next

Got this wrong? Here's your next step.

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 350-401 ACL questions on filtering logic and placement.

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FAQ

Questions learners often ask

What does this 350-401 question test?

ACLs and CoPP — This question tests ACLs and CoPP — Standard ACLs match source addresses..

What is the correct answer to this question?

The correct answer is: The CoPP policy is policing ICMP traffic to a rate that is too low for the monitoring server's traffic. — The correct answer is that the CoPP policy is policing ICMP traffic to a rate that is too low for the monitoring server's traffic. Option B is incorrect because the ACL is not mentioned as blocking ICMP. Option C is incorrect because the monitoring server is not the source of the issue; it is the target. Option D is incorrect because the switch's CPU is not necessarily overloaded; the drops are due to CoPP policing.

What should I do if I get this 350-401 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?

Standard ACLs match source addresses.

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