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300-410 Practice Question: An engineer configures CoPP on a router with the…
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?
⚠ Common exam trap
Cisco often tests the misconception that CoPP only affects the protected class, but the trap here is that the class-default policer can starve essential control-plane traffic (like ARP) that is not explicitly matched, causing CPU issues even when OSPF appears healthy.
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 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 too low to handle essential control-plane traffic like ARP, which falls into class-default. When ARP packets are dropped, the router must retry ARP resolution, generating additional CPU overhead from policing and retransmissions, keeping CPU utilization high. OSPF neighbors form because OSPF traffic is explicitly protected in the PROTECT class with a 1000 pps policer, but the underlying ARP starvation causes CPU strain.
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.
- ✗
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.
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.