Question 591 of 2,152

Control Plane Policing (CoPP) →hardMultiple ChoiceObjective-mapped

300-410 Control Plane Policing (CoPP) Practice Question

This 300-410 practice question tests your understanding of control plane policing (copp). Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 notices that BGP sessions between two directly connected routers are flapping every few minutes. The routers are running IOS-XE 17.3 and have CoPP enabled. The engineer checks the CoPP policy and sees a class-map matching BGP packets with a police rate of 8000 bps. The BGP session uses MD5 authentication and the routers exchange a full BGP table with 500,000 prefixes. What is the most likely cause of the BGP session flapping?

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 1hardmultiple choice

Open the full BGP breakdown →

A
The BGP MD5 authentication is causing excessive CPU utilization, triggering CoPP drops.
Why wrong: MD5 authentication adds CPU overhead but does not cause CoPP drops if the police rate is adequate. The issue is the police rate being too low.
B
The CoPP police rate of 8000 bps is too low for the BGP keepalive and update traffic, causing packet drops.
BGP with 500,000 prefixes generates significant update traffic, and 8000 bps is insufficient, leading to dropped packets and session flapping.
C
The CoPP class-map is not matching BGP packets correctly because it uses a wrong access-list.
Why wrong: While possible, the scenario states the class-map matches BGP packets, and the symptom is directly related to the police rate being too low.
D
The BGP hold timer is set too low, causing the session to reset before CoPP drops are noticed.
Why wrong: The hold timer default is 180 seconds; session flapping every few minutes suggests CoPP drops are the cause, not the hold timer.

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 police rate of 8000 bps is too low for the BGP keepalive and update traffic, causing packet drops.

The CoPP policy is policing BGP control plane packets at a rate of 8000 bps, which is insufficient for the BGP keepalive and update traffic. BGP keepalives are sent every 60 seconds by default, but with 500,000 prefixes, the initial BGP update traffic can easily exceed 8000 bps, causing packets to be dropped and the session to flap.

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 BGP MD5 authentication is causing excessive CPU utilization, triggering CoPP drops.
Why it's wrong here
MD5 authentication adds CPU overhead but does not cause CoPP drops if the police rate is adequate. The issue is the police rate being too low.
✓
The CoPP police rate of 8000 bps is too low for the BGP keepalive and update traffic, causing packet drops.
Why this is correct
BGP with 500,000 prefixes generates significant update traffic, and 8000 bps is insufficient, leading to dropped packets and session flapping.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✗
The CoPP class-map is not matching BGP packets correctly because it uses a wrong access-list.
Why it's wrong here
While possible, the scenario states the class-map matches BGP packets, and the symptom is directly related to the police rate being too low.
✗
The BGP hold timer is set too low, causing the session to reset before CoPP drops are noticed.
Why it's wrong here
The hold timer default is 180 seconds; session flapping every few minutes suggests CoPP drops are the cause, not the hold timer.

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

Scenario analysis trap
While possible, the scenario states the class-map matches BGP packets, and the symptom is directly related to the police rate being too low.

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 300-410 ACL questions on filtering logic and placement.

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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) — Standard ACLs match source addresses..

What is the correct answer to this question?

The correct answer is: The CoPP police rate of 8000 bps is too low for the BGP keepalive and update traffic, causing packet drops. — The CoPP policy is policing BGP control plane packets at a rate of 8000 bps, which is insufficient for the BGP keepalive and update traffic. BGP keepalives are sent every 60 seconds by default, but with 500,000 prefixes, the initial BGP update traffic can easily exceed 8000 bps, causing packets to be dropped and the session to flap.

What should I do if I get this 300-410 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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