Question 1,436 of 2,152

Device Management →hardMultiple ChoiceObjective-mapped

CoPP Breaks OSPF: class-default Policing Drops Hello Packets

This 300-410 practice question tests your understanding of device management. 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 configures Control Plane Policing (CoPP) on a router to protect the control plane. After applying the policy, OSPF adjacencies go down. The policy includes a class that matches OSPF traffic with a police rate of 1000 pps. Which is the most likely explanation?

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 OSPF traffic is matched by class-default, which has a low police rate or is set to drop, causing hello packets to be dropped.
If OSPF is not explicitly matched in a higher class, it falls to class-default, which may have a restrictive policy.
B
The police rate of 1000 pps is too low for OSPF hello packets.
Why wrong: OSPF hello packets are small and infrequent; 1000 pps is more than sufficient.
C
CoPP only applies to management traffic, not routing protocols.
Why wrong: CoPP applies to all control plane traffic, including routing protocols.
D
The OSPF process is not configured to use the control plane policy.
Why wrong: CoPP is applied globally to the control plane, not per process.

Full breakdown with real-world context →

Quick Answer

The answer is that OSPF adjacencies are dropping because the OSPF traffic is being matched by class-default, which is policing or dropping packets. Even though a separate class was configured to match OSPF with a police rate of 1000 pps, the Control Plane Policing (CoPP) policy processes traffic sequentially, and if OSPF packets do not match that specific class—often due to a misconfigured match statement or order—they fall into class-default. This default class typically has an implicit or explicit low police rate, or even a drop action, which causes OSPF hello packets to be discarded, breaking the adjacency. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of CoPP traffic classification order and the critical role of class-default as a catch-all. A common trap is assuming a dedicated OSPF class alone guarantees protection; in reality, any unmatched traffic, including OSPF, is subject to the default class. Memory tip: “If it’s not matched, it’s defaulted—and defaulted OSPF means dropped neighbors.”

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 OSPF traffic is matched by class-default, which has a low police rate or is set to drop, causing hello packets to be dropped.

Option A is correct because when CoPP is applied, any traffic not explicitly matched by a user-defined class falls into class-default. If class-default has a low police rate or is configured to drop packets, OSPF hello packets (which are critical for adjacency maintenance) will be dropped, causing OSPF adjacencies to go down. The OSPF traffic is likely not being matched by the intended class due to incorrect classification or ordering, leaving it to be processed by class-default.

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 OSPF traffic is matched by class-default, which has a low police rate or is set to drop, causing hello packets to be dropped.
Why this is correct
If OSPF is not explicitly matched in a higher class, it falls to class-default, which may have a restrictive policy.
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 of 1000 pps is too low for OSPF hello packets.
Why it's wrong here
OSPF hello packets are small and infrequent; 1000 pps is more than sufficient.
✗
CoPP only applies to management traffic, not routing protocols.
Why it's wrong here
CoPP applies to all control plane traffic, including routing protocols.
✗
The OSPF process is not configured to use the control plane policy.
Why it's wrong here
CoPP is applied globally to the control plane, not per process.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the misconception that CoPP only affects management traffic, but the trap here is that class-default can inadvertently drop critical routing protocol packets if not properly configured, leading to adjacency loss.

Detailed technical explanation

How to think about this question

CoPP uses MQC (Modular QoS CLI) to classify traffic into classes and apply police actions. The 'class-default' is the implicit final class in a policy-map, and if not explicitly configured with a police rate, it defaults to 'transmit' (no policing). However, if an engineer mistakenly sets class-default to 'drop' or a very low rate, all unmatched traffic—including OSPF—is affected. A real-world scenario is when an engineer applies a restrictive CoPP policy to mitigate DoS attacks but forgets to include routing protocol traffic in a permit class, causing routing instability.

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?

Device Management — This question tests Device Management — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The OSPF traffic is matched by class-default, which has a low police rate or is set to drop, causing hello packets to be dropped. — Option A is correct because when CoPP is applied, any traffic not explicitly matched by a user-defined class falls into class-default. If class-default has a low police rate or is configured to drop packets, OSPF hello packets (which are critical for adjacency maintenance) will be dropped, causing OSPF adjacencies to go down. The OSPF traffic is likely not being matched by the intended class due to incorrect classification or ordering, leaving it to be processed by class-default.

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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