The answer is that the class-default police rate is too low, causing the router to drop essential ARP packets while still consuming CPU cycles due to policing overhead. This occurs because CoPP applies a 1000 pps limit to OSPF traffic, but all other traffic—including ARP, which is critical for neighbor discovery and Layer 2 resolution—is restricted to only 500 pps in the class-default. When ARP requests exceed that low rate, they are dropped, yet the router’s CPU remains high because the policing process itself requires processing cycles to evaluate and drop packets, and OSPF traffic is still being forwarded at its allowed rate. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding that CoPP can inadvertently starve control-plane protocols not explicitly matched, and a common trap is assuming high CPU always means too much traffic is passing rather than being policed. Remember the mnemonic: “Low default, high overhead—ARP drops don’t save the CPU.”
300-410 Control Plane Policing (CoPP) Practice Question
This 300-410 practice question tests your understanding of control plane policing (copp). The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 CoPP on a router with the following policy: class-map match-any PROTECT, match protocol ospf, police 1000 pps; class class-default, police 500 pps. After applying, OSPF neighbors form, but the router's CPU utilization remains high. 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The class-default police rate is too low, causing ARP packets to be dropped, but CPU is high due to the policing overhead.
The class-default police rate of 500 pps is lower than the OSPF class rate of 1000 pps. However, traffic not matching OSPF (e.g., ARP, ICMP) is limited to 500 pps. If such traffic exceeds 500 pps, it is dropped, but the CPU may still be high due to the policing process itself or because OSPF traffic is still allowed at 1000 pps. The edge case is that the class-default rate may be too low, causing drops of essential traffic like ARP, but the CPU issue persists because the router is still processing the policed 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 class-default police rate is too low, causing ARP packets to be dropped, but CPU is high due to the policing overhead.
Why this is correct
Policing itself consumes CPU, and dropping packets may cause retries, increasing CPU.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
OSPF traffic is being policed to 1000 pps, which is too high, causing CPU overload.
Why it's wrong here
A higher rate allows more traffic, not less.
✗
CoPP only works on hardware-switched platforms, not software.
Why it's wrong here
CoPP works on both, but CPU impact varies.
✗
The class-default should have a higher rate than the OSPF class.
Why it's wrong here
There is no such requirement; the issue is the policing overhead.
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.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
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.
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 class-default police rate is too low, causing ARP packets to be dropped, but CPU is high due to the policing overhead. — The class-default police rate of 500 pps is lower than the OSPF class rate of 1000 pps. However, traffic not matching OSPF (e.g., ARP, ICMP) is limited to 500 pps. If such traffic exceeds 500 pps, it is dropped, but the CPU may still be high due to the policing process itself or because OSPF traffic is still allowed at 1000 pps. The edge case is that the class-default rate may be too low, causing drops of essential traffic like ARP, but the CPU issue persists because the router is still processing the policed packets.
What should I do if I get this 300-410 question wrong?
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.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.