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300-410 Practice Question: An engineer configures Control Plane Policing…
An engineer configures Control Plane Policing (CoPP) on a router to protect the control plane. After applying the policy, OSPF neighbors go down. The CoPP policy has a class that matches OSPF traffic with a rate-limit of 100 pps. Which is the most likely explanation?
⚠ Common exam trap
Cisco often tests the misconception that CoPP is applied per-interface or that the default class is the culprit, but the real trap is understanding that control plane protocols like OSPF require consistent, low-latency delivery of Hello packets, and any rate limit—even one that seems high—can cause neighbor loss if it doesn't account for burst behavior.
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 being dropped because the rate-limit is too low for the hello interval.
OSPF uses Hello packets to establish and maintain neighbor adjacencies, typically sent every 10 seconds on broadcast networks. If the CoPP rate-limit of 100 pps is too low to accommodate the burst of OSPF Hello packets (e.g., during neighbor initialization or network convergence), the policer will drop excess packets, causing the OSPF dead timer to expire and neighbors to go down. This is the most direct cause because the policy explicitly matches OSPF traffic and applies a strict rate limit that can starve the control plane of necessary protocol messages.
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 being dropped because the rate-limit is too low for the hello interval.
Why this is correct
Correct. Low pps rate can drop OSPF hellos, causing neighbor loss.
- ✗
The CoPP policy is applied to the wrong interface.
Why it's wrong here
CoPP is applied globally to control plane, not per interface.
- ✗
The OSPF traffic is matched by the default class and dropped.
Why it's wrong here
If OSPF is explicitly matched, default class does not apply.
- ✗
The CoPP policy uses 'police' instead of 'rate-limit'.
Why it's wrong here
Both can be used; syntax difference does not cause drop.
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.