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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 SNMP. The engineer checks the policy and confirms that the class-map for SSH and SNMP traffic is set to 'permit'. What 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', causing all unmatched traffic to be dropped, including SSH and SNMP if they are not correctly classified.

A common edge case with CoPP is that the default class class-default is often set to 'drop' or 'police' with a very low rate, which can drop all traffic not explicitly matched by other classes. Even if SSH and SNMP are permitted, if the class-default is set to drop, any traffic that does not match the explicit classes (e.g., due to a misclassification) will be dropped. Additionally, the order of class-maps matters; if a broader class matches before the specific one, the traffic may be policed incorrectly.

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', causing all unmatched traffic to be dropped, including SSH and SNMP if they are not correctly classified.

    Why this is correct

    In CoPP, the class-default is the default class for all traffic not matched by other classes. If it is set to drop, any traffic that does not match the explicit classes will be dropped. If SSH or SNMP traffic is not correctly matched by the class-map (e.g., due to a typo in the access-list), it will fall into class-default and be dropped.

  • ✗

    The 'rate-limit' is configured in bps instead of pps, causing excessive policing.

    Why it's wrong here

    While unit mismatch can cause issues, it would not cause complete unreachability unless the rate is set to 0. The question states the policy is applied, but the router becomes unreachable, suggesting dropping rather than policing.

  • ✗

    The 'service-policy' is applied to the control-plane input direction, but SSH and SNMP are output traffic.

    Why it's wrong here

    SSH and SNMP traffic to the router is input traffic to the control plane, so applying CoPP input is correct. Output CoPP is for traffic originated by the router.

  • ✗

    The class-map for SSH and SNMP uses a 'match-all' condition, but the access-list has multiple entries that are ORed.

    Why it's wrong here

    Using 'match-all' with an access-list is fine; the access-list entries are ORed by default. This would not cause the traffic to be dropped.

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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.