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.

Question 1hardmultiple choice

Open the full BGP breakdown →

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-BGP class shows zero packets, but the BGP session is established and exchanging messages. This indicates that BGP traffic is not being classified by the CoPP-BGP class, likely because the access-group 120 is not matching the BGP packets. The BGP session is up, so the traffic is being processed by the class-default instead.

Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.

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
OSPF neighbours must agree on key parameters.
✗
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: OSPF can fail even when IP connectivity looks correct

OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.

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

OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.

KKey Concepts to Remember

OSPF neighbours must agree on key parameters.
Router ID selection can affect neighbour relationships and LSDB output.
OSPF cost influences the preferred path.
A route can appear in OSPF information but not become the installed route.

TExam Day Tips

Check area mismatch first when OSPF adjacency fails.
Review passive interfaces when a network is advertised but no neighbour forms.
Use show ip ospf neighbor and show ip route clues carefully.

Key takeaway

OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.

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.

What to study next

Got this wrong? Here's your next step.

Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.

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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) — OSPF neighbours must agree on key parameters..

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-BGP class shows zero packets, but the BGP session is established and exchanging messages. This indicates that BGP traffic is not being classified by the CoPP-BGP class, likely because the access-group 120 is not matching the BGP packets. The BGP session is up, so the traffic is being processed by the class-default instead.

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?

OSPF neighbours must agree on key parameters.

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