Question 878 of 2,152
Control Plane Policing (CoPP)mediumMultiple ChoiceObjective-mapped

CoPP Selective SSH Rate-Limiting

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.

A router experiences high CPU utilization due to SSH login attempts from an external attacker. The network engineer implements a CoPP policy to rate-limit SSH traffic to 10000 bps. After applying the policy, the engineer notices that legitimate SSH sessions from the management network are also being dropped intermittently. The CoPP policy uses a class-map that matches TCP port 22 traffic. What should the engineer do to fix this issue?

Quick Answer

The correct solution is to create a separate class for legitimate SSH traffic from the management network with a higher police rate, while policing the attacker’s traffic more aggressively. This is necessary because the current CoPP policy applies a single rate-limit to all TCP port 22 traffic, which cannot distinguish between malicious SSH login attempts and legitimate management sessions. By implementing a more granular class-map that matches only the attacker’s source IP addresses or by classifying traffic from the trusted management subnet with a higher police rate, the engineer achieves selective SSH rate-limiting without dropping authorized connections. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of Control Plane Policing granularity and the importance of using ACLs or object-groups within class-maps to differentiate traffic flows. A common trap is assuming a single police rate for a protocol is sufficient, but the exam emphasizes that CoPP policies must be source-aware to preserve legitimate access. Memory tip: “One rate for all will drop the ball—separate the good from the bad to keep the network glad.”

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

Create a separate class for legitimate SSH traffic from the management network with a higher police rate, and police the attacker's traffic more aggressively.

Option C is correct because it uses a granular CoPP design: legitimate SSH traffic from the management network is placed in a separate class with a higher police rate, while the attacker's traffic is policed more aggressively. This preserves control-plane resources for authorized sessions without dropping them, addressing the root cause of the problem—overly broad rate-limiting of all TCP port 22 traffic.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • Increase the police rate for the SSH class to 100000 bps to allow all SSH traffic.

    Why it's wrong here

    This would allow the attacker's traffic as well, defeating the purpose of CoPP and potentially still causing high CPU.

  • Modify the class-map to match only SSH traffic from the attacker's source IP addresses using an access-list.

    Why it's wrong here

    The goal is to block the attacker, not match them. The engineer should match legitimate sources and police the attacker separately.

  • Create a separate class for legitimate SSH traffic from the management network with a higher police rate, and police the attacker's traffic more aggressively.

    Why this is correct

    This allows legitimate SSH sessions to pass while still protecting the control plane from the attacker.

    Related concept

    Read the scenario before looking for a memorised answer.

  • Remove the CoPP policy and implement an ACL on the interface to block the attacker's IP address.

    Why it's wrong here

    This is a valid alternative but does not fix the CoPP issue; the question asks what to do to fix the issue with the current CoPP policy.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the misconception that simply increasing the police rate or blocking a single attacker IP is sufficient, when the correct solution requires differentiated treatment of trusted versus untrusted traffic within the same protocol class.

Detailed technical explanation

How to think about this question

CoPP uses MQC (Modular QoS CLI) to classify control-plane traffic and apply policing actions. When a single class matches all TCP port 22 traffic, the police rate is applied to the aggregate of all SSH packets, causing legitimate sessions to be dropped when the attacker's traffic bursts exceed the rate. By creating separate classes—one for trusted management sources (matched via an access-list) and another for all other SSH traffic—the engineer can assign a higher committed information rate (CIR) to legitimate traffic and a lower CIR (or drop action) to attacker traffic, ensuring control-plane resources are allocated appropriately.

KKey Concepts to Remember

  • Read the scenario before looking for a memorised answer.
  • Find the constraint that changes the correct option.
  • Eliminate answers that are true in general but not in this case.

TExam Day Tips

  • Watch for words such as best, first, most likely and least administrative effort.
  • Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.

What to study next

Got this wrong? Here's your next step.

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FAQ

Questions learners often ask

What does this 300-410 question test?

Control Plane Policing (CoPP) — This question tests Control Plane Policing (CoPP) — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: Create a separate class for legitimate SSH traffic from the management network with a higher police rate, and police the attacker's traffic more aggressively. — Option C is correct because it uses a granular CoPP design: legitimate SSH traffic from the management network is placed in a separate class with a higher police rate, while the attacker's traffic is policed more aggressively. This preserves control-plane resources for authorized sessions without dropping them, addressing the root cause of the problem—overly broad rate-limiting of all TCP port 22 traffic.

What should I do if I get this 300-410 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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Last reviewed: Jul 4, 2026

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