Question 1,563 of 2,152

Control Plane Policing (CoPP) →mediumMultiple ChoiceObjective-mapped

CoPP Default Class Dropping OSPF Packets

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.

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 →

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.”

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.

The CoPP policy includes a class-map that matches only ICMP traffic, but when applied, it uses a default class that drops all unmatched traffic. OSPF hello packets, which are not ICMP, fall into this default class and are dropped, causing adjacencies to fail. This is a common misconfiguration where the policy lacks an explicit permit for essential control plane protocols like OSPF.

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

Cisco often tests the trap that candidates assume only the explicitly matched class affects traffic, forgetting that the default class in a CoPP policy drops all unmatched traffic unless explicitly configured otherwise.

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

CoPP uses a control-plane service policy that classifies traffic destined to the router's control plane. If the policy does not include an explicit class to permit OSPF (protocol 89) or a default class that allows it, the implicit default action is to drop unmatched packets. In real-world deployments, engineers must ensure that routing protocol packets like OSPF, BGP, and EIGRP are explicitly permitted or rate-limited appropriately to avoid adjacency loss.

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

Quick reference

Routing Protocol Comparison

Protocol	Metric	Max Hops	Algorithm	Type
RIP v2	Hop count	15	Bellman-Ford	Distance vector
OSPF	Cost (bandwidth)	Unlimited	Dijkstra (SPF)	Link state
EIGRP	Composite metric	Unlimited	DUAL	Hybrid
IS-IS	Cost	Unlimited	Dijkstra	Link state
BGP	Policy / attributes	Unlimited	Path vector	Path vector

RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.

What to study next

Got this wrong? Here's your next step.

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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 policy has a default class that drops all unmatched traffic, including OSPF packets. — The CoPP policy includes a class-map that matches only ICMP traffic, but when applied, it uses a default class that drops all unmatched traffic. OSPF hello packets, which are not ICMP, fall into this default class and are dropped, causing adjacencies to fail. This is a common misconfiguration where the policy lacks an explicit permit for essential control plane protocols like OSPF.

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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