Question 1,675 of 2,152

VRF-Lite →hardMultiple ChoiceObjective-mapped

CoPP Interaction with VRF-Lite: Why SSH is Dropped

This 300-410 practice question tests your understanding of vrf-lite. 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 network engineer applies a CoPP (Control Plane Policing) policy to a router running VRF-Lite. The policy includes a class that matches SSH traffic and polices it to 1 Mbps. After applying the policy, the engineer cannot SSH into the router from any VRF. Which is the most likely explanation?

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 an explicit 'deny' in the class-default, which drops all traffic not matched by other classes.
If class-default has a 'police' or 'drop' action, all unmatched traffic (including SSH) is dropped. The engineer should have added a 'class class-default' with 'police' or 'permit'.
B
The SSH traffic is being policed to 1 Mbps, but the traffic rate is below that, so it should be allowed.
Why wrong: If the traffic is below the police rate, it should be allowed. The issue is not the police rate but the classification.
C
The CoPP policy is applied to the control plane of the VRF, not the global control plane, so it does not affect SSH traffic.
Why wrong: CoPP is applied globally to the control plane, not per-VRF. There is no per-VRF CoPP.
D
The SSH traffic is being matched by a different class that has a 'drop' action, such as a class for ICMP.
Why wrong: This is possible but less likely than the default class issue. The question states the policy includes a class for SSH, so it should match.

Full breakdown with real-world context →

Quick Answer

The answer is that the CoPP policy’s class-default has an explicit ‘deny’ action, which drops all traffic not matched by other classes, including SSH from any VRF. This happens because CoPP policies are applied globally to the control plane and classify traffic using the global routing table, regardless of VRF context. When SSH traffic originates from a VRF-Lite instance, the class-map—whether using ‘match protocol’ or ‘match access-group’—evaluates it in the global table, so if the SSH class is not explicitly matched, the traffic falls into class-default and is dropped by the policer. On the Cisco CCNP ENARSI 300-410 exam, this tests your understanding that CoPP interacts with VRF-Lite by ignoring VRF separation during classification, a common trap where engineers assume VRF-aware classification. A key memory tip: “CoPP sees the global table, not the VRF label—if class-default denies, SSH from any VRF is gone.”

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 an explicit 'deny' in the class-default, which drops all traffic not matched by other classes.

CoPP policies are applied to the control plane and affect all traffic destined to the router, regardless of VRF. However, CoPP uses the global routing table for classification. If the SSH traffic is sourced from a VRF, the CoPP policy may not match it correctly because the class-map might be using 'match protocol' or 'match access-group' that is evaluated in the global context. Additionally, the default class (class-default) often has a police action that drops traffic if not explicitly allowed. A common edge case is that the engineer forgot to include a 'class-default' action to permit traffic, causing all unmatched traffic to be dropped.

Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.

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 an explicit 'deny' in the class-default, which drops all traffic not matched by other classes.
Why this is correct
If class-default has a 'police' or 'drop' action, all unmatched traffic (including SSH) is dropped. The engineer should have added a 'class class-default' with 'police' or 'permit'.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✗
The SSH traffic is being policed to 1 Mbps, but the traffic rate is below that, so it should be allowed.
Why it's wrong here
If the traffic is below the police rate, it should be allowed. The issue is not the police rate but the classification.
✗
The CoPP policy is applied to the control plane of the VRF, not the global control plane, so it does not affect SSH traffic.
Why it's wrong here
CoPP is applied globally to the control plane, not per-VRF. There is no per-VRF CoPP.
✗
The SSH traffic is being matched by a different class that has a 'drop' action, such as a class for ICMP.
Why it's wrong here
This is possible but less likely than the default class issue. The question states the policy includes a class for SSH, so it should match.

Common exam traps

Common exam trap: ACLs stop at the first match

ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.

Detailed technical explanation

How to think about this question

ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.

KKey Concepts to Remember

Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.

TExam Day Tips

Check inbound versus outbound direction.
Read the ACL from top to bottom.
Look for a broader permit or deny above the intended line.

Key takeaway

ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.

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.

Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related 300-410 ACL questions on filtering logic and placement.

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FAQ

Questions learners often ask

What does this 300-410 question test?

VRF-Lite — This question tests VRF-Lite — Standard ACLs match source addresses..

What is the correct answer to this question?

The correct answer is: The CoPP policy has an explicit 'deny' in the class-default, which drops all traffic not matched by other classes. — CoPP policies are applied to the control plane and affect all traffic destined to the router, regardless of VRF. However, CoPP uses the global routing table for classification. If the SSH traffic is sourced from a VRF, the CoPP policy may not match it correctly because the class-map might be using 'match protocol' or 'match access-group' that is evaluated in the global context. Additionally, the default class (class-default) often has a police action that drops traffic if not explicitly allowed. A common edge case is that the engineer forgot to include a 'class-default' action to permit traffic, causing all unmatched traffic to be dropped.

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

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?

Standard ACLs match source addresses.

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