Question 34 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). Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 policy-map control-plane

Control Plane

Service-policy input: CoPP-IN

Class-map: CoPP-BGP (match-all) 0 packets, 0 bytes 5 minute offered rate 0000 bps, drop rate 0000 bps Match: access-group 120 police: cir 32000 bps, bc 6000 bytes, be 6000 bytes conformed 0 packets, 0 bytes; actions: transmit exceeded 0 packets, 0 bytes; actions: drop violated 0 packets, 0 bytes; actions: drop

R1# show ip bgp summary

BGP router identifier 1.1.1.1, local AS number 100 BGP table version is 1, main routing table version 1

Neighbor        V           AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
10.1.1.2        4          200      10      10        1    0    0 00:05:00        5

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.

A
The BGP session is down.
Why wrong: The BGP summary shows the neighbor is up with state established.
B
The access-list 120 is not matching BGP traffic, so it is falling into class-default.
The zero packet count indicates the class is not matching, but BGP is working, so traffic is matched by class-default.
C
The police rate is too low and is dropping all BGP packets.
Why wrong: The counters show 0 packets, so no packets have been classified.
D
The policy-map is applied to the output direction.
Why wrong: The output shows input direction.

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 access-list 120 is not matching BGP traffic, so it is falling into class-default.

The CoPP policy shows zero packets matched under class CoPP-BGP, which uses access-group 120. Since the BGP session to 10.1.1.2 is up and exchanging routes, BGP traffic is not being classified by the policy and is instead falling into the default class, which typically permits all traffic. This indicates that access-list 120 does not match the BGP packets, likely due to incorrect ACL entries or direction.

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 session is down.
Why it's wrong here
The BGP summary shows the neighbor is up with state established.
✓
The access-list 120 is not matching BGP traffic, so it is falling into class-default.
Why this is correct
The zero packet count indicates the class is not matching, but BGP is working, so traffic is matched by class-default.
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 police rate is too low and is dropping all BGP packets.
Why it's wrong here
The counters show 0 packets, so no packets have been classified.
✗
The policy-map is applied to the output direction.
Why it's wrong here
The output shows input direction.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the misconception that a zero packet count under a CoPP class implies the policer is dropping all traffic, when in fact it indicates the classification is failing and traffic is not being evaluated by that policy.

Trap categories for this question

Command / output trap
The BGP summary shows the neighbor is up with state established.

Detailed technical explanation

How to think about this question

CoPP uses class-maps to match control-plane traffic via access-lists or other criteria, and the policer enforces rate limits. If the ACL does not match the source/destination IPs or protocol (e.g., TCP port 179 for BGP), packets bypass the policy and are handled by the default class, which often has no policing. In production, misconfigured ACLs are a common cause of CoPP ineffectiveness, as the control-plane CPU remains unprotected against the intended traffic.

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 network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.

Visual reference

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 access-list 120 is not matching BGP traffic, so it is falling into class-default. — The CoPP policy shows zero packets matched under class CoPP-BGP, which uses access-group 120. Since the BGP session to 10.1.1.2 is up and exchanging routes, BGP traffic is not being classified by the policy and is instead falling into the default class, which typically permits all traffic. This indicates that access-list 120 does not match the BGP packets, likely due to incorrect ACL entries or direction.

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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