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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, the router becomes unreachable via SSH, and OSPF neighbor adjacencies go down. The engineer checks the CoPP policy and sees that the class-map for SSH and OSPF traffic is configured with a police rate. Which is the most likely explanation?
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 is set to drop all traffic not matched by explicit classes
A common edge case with CoPP is that the default class (class-default) is often configured with an explicit deny or a very low rate, which can drop all traffic not matched by other classes. If the engineer does not include a 'class class-default' with an appropriate action (e.g., 'police' with a conform action of 'transmit'), all unmatched traffic, including critical control plane traffic, may be dropped. Additionally, if the police rate is too low for OSPF hello packets, adjacencies can fail.
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 is set to drop all traffic not matched by explicit classes
Why this is correct
Correct. If class-default drops traffic, OSPF and SSH packets that are not explicitly permitted will be dropped.
- ✗
The police rate for OSPF traffic is too high
Why it's wrong here
A high police rate would not cause drops; a low rate would.
- ✗
The CoPP policy is applied to the wrong interface
Why it's wrong here
CoPP is applied globally, not per interface.
- ✗
The class-map for SSH uses the wrong match criteria
Why it's wrong here
If the match criteria were wrong, SSH traffic might not be classified, but the issue is more likely the default class.
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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JA
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.