Question 1,170 of 2,152

Control Plane Policing (CoPP) →mediumMultiple ChoiceObjective-mapped

Why a Low CoPP Police Rate Drops EIGRP Packets and Causes Adjacency Flaps

This 300-410 practice question tests your understanding of control plane policing (copp). Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 router running EIGRP has a CoPP policy that includes a class-map matching EIGRP packets with a police rate of 2000 bps. The network engineer notices that EIGRP neighbor adjacencies are flapping. The EIGRP network has 100 routes. The engineer checks the CoPP statistics and sees that the EIGRP class has dropped 500 packets in the last hour. What is the most likely root 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 EIGRP hello interval is set too low, causing excessive hello packets that exceed the police rate.
Why wrong: The hello interval default is 5 seconds; even if set lower, the police rate should be adjusted accordingly, but the root cause is the police rate being too low.
B
The CoPP police rate of 2000 bps is insufficient for EIGRP hello and update traffic, causing packet drops.
EIGRP packets, though small, can be dropped if the police rate is too low, leading to adjacency flapping.
C
The EIGRP authentication is causing larger packets that exceed the police rate.
Why wrong: EIGRP authentication adds a small overhead but not enough to cause significant drops with 2000 bps.
D
The CoPP class-map is matching EIGRP packets incorrectly, causing them to be dropped by a default class.
Why wrong: The statistics show drops in the EIGRP class, so the class is matching correctly.

Full breakdown with real-world context →

Quick Answer

The answer is that the CoPP police rate of 2000 bps is insufficient for EIGRP hello and update traffic, causing packet drops and adjacency flaps. EIGRP sends small hello packets every 5 seconds by default, and with 100 routes, the update traffic remains modest, but a police rate this low means even these small packets exceed the token bucket capacity, leading to drops. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of how CoPP interacts with routing protocol keepalives—a common trap is assuming a low drop count is harmless, when in fact even a few dropped hellos can tear down adjacencies. Remember that EIGRP hellos are tiny but frequent, so a police rate must accommodate both the burst of updates and the steady hello stream. Memory tip: “Hellos are small but they come often; a low CoPP rate makes neighbors soften.”

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 police rate of 2000 bps is insufficient for EIGRP hello and update traffic, causing packet drops.

The CoPP police rate of 2000 bps is too low for EIGRP traffic. EIGRP hello packets are sent every 5 seconds (default) and are typically around 60-80 bytes each, plus periodic updates and queries. With 100 routes, the initial exchange and any topology changes generate significant update traffic. Dropping 500 packets in an hour confirms the rate is insufficient, causing hello loss and neighbor flapping.

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 EIGRP hello interval is set too low, causing excessive hello packets that exceed the police rate.
Why it's wrong here
The hello interval default is 5 seconds; even if set lower, the police rate should be adjusted accordingly, but the root cause is the police rate being too low.
✓
The CoPP police rate of 2000 bps is insufficient for EIGRP hello and update traffic, causing packet drops.
Why this is correct
EIGRP packets, though small, can be dropped if the police rate is too low, leading to adjacency flapping.
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 EIGRP authentication is causing larger packets that exceed the police rate.
Why it's wrong here
EIGRP authentication adds a small overhead but not enough to cause significant drops with 2000 bps.
✗
The CoPP class-map is matching EIGRP packets incorrectly, causing them to be dropped by a default class.
Why it's wrong here
The statistics show drops in the EIGRP class, so the class is matching correctly.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the misconception that CoPP drops are always due to misconfiguration or authentication overhead, when in fact the police rate is simply too low for the protocol's normal operation, especially with a moderate number of routes.

Trap categories for this question

Command / output trap
The statistics show drops in the EIGRP class, so the class is matching correctly.

Detailed technical explanation

How to think about this question

EIGRP uses RTP (Reliable Transport Protocol) for updates and queries, which can generate bursts of traffic during convergence. The 2000 bps rate is roughly 250 bytes per second, which is easily exceeded by a single EIGRP update packet (e.g., a 1500-byte MTU-sized update) or by multiple hello packets. In real-world scenarios, CoPP for routing protocols should be set based on worst-case traffic, including hellos, updates, and queries, often requiring rates of 10-100 kbps for stability.

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.

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.

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 CoPP police rate of 2000 bps is insufficient for EIGRP hello and update traffic, causing packet drops. — The CoPP police rate of 2000 bps is too low for EIGRP traffic. EIGRP hello packets are sent every 5 seconds (default) and are typically around 60-80 bytes each, plus periodic updates and queries. With 100 routes, the initial exchange and any topology changes generate significant update traffic. Dropping 500 packets in an hour confirms the rate is insufficient, causing hello loss and neighbor flapping.

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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