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.

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 police rate of 8000 bps is insufficient for the BGP traffic generated by exchanging a full BGP table of 500,000 prefixes. BGP updates for such a large table can easily exceed 8000 bps, especially when combined with keepalive messages. When the police rate is exceeded, CoPP drops BGP packets, causing the session to flap as the hold timer expires due to missing keepalives or updates.

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.

✗
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
Read the scenario before looking for a memorised answer.
✗
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: answer the scenario, not the keyword

Cisco often tests the misconception that MD5 authentication causes CPU spikes leading to CoPP drops, but the real issue is that CoPP police rates must be sized to accommodate the actual BGP traffic volume, especially during full table exchanges.

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

BGP updates for 500,000 prefixes can be several megabytes in size, easily exceeding 8000 bps (1 KB/s). CoPP uses a token bucket policer; when the rate is exceeded, packets are dropped, which disrupts BGP keepalives and updates. In production, CoPP for BGP should be configured with a reasonable rate (e.g., 256,000 bps or higher) based on the expected update size and frequency, and the class-map should match on BGP TCP port 179 with a specific access-list to avoid unintended drops.

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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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: The CoPP police rate of 8000 bps is too low for the BGP keepalive and update traffic, causing packet drops. — The CoPP police rate of 8000 bps is insufficient for the BGP traffic generated by exchanging a full BGP table of 500,000 prefixes. BGP updates for such a large table can easily exceed 8000 bps, especially when combined with keepalive messages. When the police rate is exceeded, CoPP drops BGP packets, causing the session to flap as the hold timer expires due to missing keepalives or updates.

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.

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?

Read the scenario before looking for a memorised answer.

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