Question 1,563 of 2,152

Control Plane Policing (CoPP) →mediumMultiple ChoiceObjective-mapped

Quick Answer

The answer is a default class in the CoPP policy that drops all unmatched traffic, including OSPF packets. This occurs because OSPF uses IP protocol 89, which is not matched by a class-map designed for ICMP (protocol 1); when no explicit match exists for OSPF, the policy’s default class—often configured with a “drop” action—silently discards those packets, breaking hello-based neighbor relationships. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding that CoPP policies require explicit classes for all critical control-plane protocols, or a permit action in the default class, to avoid accidental denial of service. A common trap is assuming only matched traffic is affected, when in reality the default class catches everything else. Memory tip: “Default drops the rest—OSPF is not ICMP, so it fails the test.”

300-410 Control Plane Policing (CoPP) Practice Question

This 300-410 practice question tests your understanding of control plane policing (copp). This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 engineer applies a CoPP policy to a router to protect the control plane. The policy includes a class-map that matches all ICMP traffic and polices it to 5000 bps. After the policy is applied, the engineer notices that OSPF adjacencies are going down. The OSPF hello packets are not being received. What is the most likely cause?

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

Review the full OSPF breakdown →

A
The CoPP policy is policing OSPF packets because the class-map matches all IP traffic, not just ICMP.
Why wrong: The scenario says the class-map matches ICMP traffic; OSPF uses IP protocol 89, so it should not be matched unless the class-map is misconfigured.
B
The CoPP policy has a default class that drops all unmatched traffic, including OSPF packets.
If the CoPP policy does not explicitly permit OSPF packets, a default drop class will cause OSPF adjacencies to fail.
C
The OSPF hello packets are being rate-limited because they are ICMP packets.
Why wrong: OSPF packets are not ICMP; they are IP protocol 89.
D
The CoPP policy is applied to the wrong interface, causing OSPF packets to be dropped.
Why wrong: CoPP is applied to the control plane, not interfaces. This is a common misconception.

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 has a default class that drops all unmatched traffic, including OSPF packets.

OSPF uses IP protocol 89, not ICMP. However, if the class-map is misconfigured to match all IP traffic or if there is a default class that drops packets, OSPF packets might be affected. The most likely cause is that the CoPP policy has a default class that drops unmatched traffic, including OSPF packets.

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 CoPP policy is policing OSPF packets because the class-map matches all IP traffic, not just ICMP.
Why it's wrong here
The scenario says the class-map matches ICMP traffic; OSPF uses IP protocol 89, so it should not be matched unless the class-map is misconfigured.
✓
The CoPP policy has a default class that drops all unmatched traffic, including OSPF packets.
Why this is correct
If the CoPP policy does not explicitly permit OSPF packets, a default drop class will cause OSPF adjacencies to fail.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
OSPF neighbours must agree on key parameters.
✗
The OSPF hello packets are being rate-limited because they are ICMP packets.
Why it's wrong here
OSPF packets are not ICMP; they are IP protocol 89.
✗
The CoPP policy is applied to the wrong interface, causing OSPF packets to be dropped.
Why it's wrong here
CoPP is applied to the control plane, not interfaces. This is a common misconception.

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

Scenario analysis trap
The scenario says the class-map matches ICMP traffic; OSPF uses IP protocol 89, so it should not be matched unless the class-map is misconfigured.

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 CoPP policy has a default class that drops all unmatched traffic, including OSPF packets. — OSPF uses IP protocol 89, not ICMP. However, if the class-map is misconfigured to match all IP traffic or if there is a default class that drops packets, OSPF packets might be affected. The most likely cause is that the CoPP policy has a default class that drops unmatched traffic, including OSPF packets.

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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