Question 629 of 2,152

Control Plane Policing (CoPP) →mediumMultiple ChoiceObjective-mapped

Why Telnet Sessions Fail Under CoPP While SSH Succeeds

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 has a CoPP policy that includes a class-map matching all TCP traffic with a police rate of 5000 bps. The engineer notices that Telnet sessions to the router are timing out, but SSH sessions work fine. The router is configured to accept both Telnet and SSH. What is the most likely cause?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

A
The CoPP policy has a separate class for Telnet with a lower police rate or a drop action.
If Telnet is in a different class with a lower rate or drop, it would explain why Telnet fails while SSH works.
B
The SSH traffic is encrypted, so it uses less bandwidth than Telnet.
Why wrong: SSH encryption adds overhead, so SSH actually uses slightly more bandwidth than Telnet.
C
The Telnet server on the router is not responding due to a configuration error.
Why wrong: The scenario states both are configured, and the issue is related to CoPP.
D
The CoPP policy is rate-limiting TCP traffic to 5000 bps, which is enough for SSH but not for Telnet.
Why wrong: Both use TCP, and 5000 bps should be sufficient for interactive sessions; the difference is likely due to separate classes.

Full breakdown with real-world context →

Quick Answer

The answer is that the CoPP policy has a separate class for Telnet with a lower police rate or a drop action. Both Telnet and SSH use TCP, so a single class matching all TCP traffic at 5000 bps would police both equally; the fact that Telnet sessions time out while SSH succeeds indicates that Telnet is being matched by a different, more restrictive class within the policy. This scenario tests your understanding of how CoPP class-maps and policy-maps interact with control plane traffic—a common trap on the Cisco CCNP ENARSI 300-410 exam is assuming a broad TCP match applies uniformly, when in reality separate classes for Telnet and SSH can have distinct police rates or actions. Remember the memory tip: “TCP is the same, but class is the game”—if one protocol fails and another succeeds under CoPP, look for a separate class targeting the failing protocol.

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 CoPP policy has a separate class for Telnet with a lower police rate or a drop action.

The correct answer is A because the CoPP policy likely includes a separate class-map that matches Telnet traffic (TCP port 23) and applies a police rate lower than 5000 bps or a drop action, causing Telnet sessions to time out. Since the existing class-map matches all TCP traffic with a 5000 bps police rate, and SSH (TCP port 22) works fine, the issue is not with the general TCP rate limit but with a more specific Telnet class that overrides or preempts the general TCP class. This is a common CoPP misconfiguration where a more specific class with a restrictive action is placed before a broader class in the policy-map.

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.

✓
The CoPP policy has a separate class for Telnet with a lower police rate or a drop action.
Why this is correct
If Telnet is in a different class with a lower rate or drop, it would explain why Telnet fails while SSH works.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The SSH traffic is encrypted, so it uses less bandwidth than Telnet.
Why it's wrong here
SSH encryption adds overhead, so SSH actually uses slightly more bandwidth than Telnet.
✗
The Telnet server on the router is not responding due to a configuration error.
Why it's wrong here
The scenario states both are configured, and the issue is related to CoPP.
✗
The CoPP policy is rate-limiting TCP traffic to 5000 bps, which is enough for SSH but not for Telnet.
Why it's wrong here
Both use TCP, and 5000 bps should be sufficient for interactive sessions; the difference is likely due to separate classes.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the concept that CoPP class-maps are processed in order, and a more specific class (e.g., matching Telnet) with a restrictive action can override a broader class (e.g., all TCP), causing candidates to incorrectly assume the general TCP rate limit is the sole cause.

Trap categories for this question

Scenario analysis trap
The scenario states both are configured, and the issue is related to CoPP.

Detailed technical explanation

How to think about this question

CoPP uses a policy-map applied to the control plane, where class-maps match traffic based on ACLs or protocols, and actions like police or drop are applied sequentially. If a class-map matching Telnet (e.g., via access-list permitting TCP port 23) is placed before the general TCP class and has a police rate of, say, 1000 bps or a drop action, Telnet packets are policed or dropped before reaching the general TCP class. In real-world scenarios, this often happens when engineers create specific classes for management protocols (SSH, Telnet, SNMP) but misconfigure the order or rate, leading to selective service degradation.

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 practitioner preparing for the 300-410 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.

What to study next

Got this wrong? Here's your next step.

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

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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: The CoPP policy has a separate class for Telnet with a lower police rate or a drop action. — The correct answer is A because the CoPP policy likely includes a separate class-map that matches Telnet traffic (TCP port 23) and applies a police rate lower than 5000 bps or a drop action, causing Telnet sessions to time out. Since the existing class-map matches all TCP traffic with a 5000 bps police rate, and SSH (TCP port 22) works fine, the issue is not with the general TCP rate limit but with a more specific Telnet class that overrides or preempts the general TCP class. This is a common CoPP misconfiguration where a more specific class with a restrictive action is placed before a broader class in the policy-map.

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.

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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