Question 900 of 2,015

SPAN and RSPAN →mediumMultiple ChoiceObjective-mapped

Quick Answer

The answer is that the destination port remains a member of a VLAN, causing the switch to process the copied SPAN frames as normal traffic, which drives high CPU utilization. When a SPAN destination port is not isolated from normal switching operations, the switch must perform Layer 2 lookups and potentially forward the copied frames back into the VLAN, creating unnecessary processing overhead. This is a common trap on the ENCOR 350-401 exam, where candidates often overlook that a SPAN destination port should be configured with commands like switchport nonegotiate and placed in a dedicated, unused VLAN to prevent the switch from treating the mirrored traffic as standard data. The scenario tests your understanding that SPAN is a CPU-intensive feature, and high CPU often stems from the destination port still participating in VLAN switching rather than from the source traffic volume itself. Memory tip: "SPAN destination ports must be VLAN-shunned—if they stay in a VLAN, CPU gets spun."

CCNP SPAN and RSPAN Practice Question

This 350-401 practice question tests your understanding of span and rspan. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 is using a Cisco Catalyst 3850 switch to monitor traffic from a server connected to port Gi1/0/1. The monitoring station is on port Gi1/0/24. The engineer configures 'monitor session 1 source interface Gi1/0/1 both' and 'monitor session 1 destination interface Gi1/0/24'. The monitoring station receives traffic, but the engineer notices that the switch CPU utilization is high. What is the most likely cause of the high CPU?

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.

Question 1mediummultiple choice

Read the full NAT/PAT explanation →

A
The SPAN session is capturing both directions, which doubles the number of packets and increases CPU usage.
Why wrong: Incorrect; capturing both directions is normal and should not cause excessive CPU if the traffic volume is not high.
B
The destination port is not configured with 'switchport nonegotiate' and is still participating in DTP, causing CPU overhead.
Why wrong: Incorrect; DTP is not related to SPAN CPU usage.
C
The destination port is still a member of a VLAN, and the switch is processing the copied frames as normal traffic, leading to high CPU.
Correct; when a destination port is not dedicated to SPAN, the switch may attempt to switch the copied frames, increasing CPU load.
D
The source interface is a trunk port, and SPAN is capturing all VLANs, causing high CPU.
Why wrong: Incorrect; the scenario does not mention trunk, and even if it were, it would not necessarily cause high CPU unless the traffic volume is high.

Full breakdown with real-world context →

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 destination port is still a member of a VLAN, and the switch is processing the copied frames as normal traffic, leading to high CPU.

SPAN can cause high CPU if the destination port is not configured with 'ingress' or if the switch is overloaded. However, a common cause is that the destination port is configured to also forward traffic normally (i.e., it is not a dedicated SPAN destination). But the question says the monitoring station receives traffic, so the destination port is working. High CPU can occur if the SPAN session is configured to capture from a large number of sources or if the switch is processing many packets. The most likely cause here is that the destination port is not configured with 'switchport nonegotiate' or is in a VLAN that causes the switch to process the copied frames as normal traffic, leading to high CPU. But the best answer: The destination port should be configured as a SPAN destination only, and if it is also a member of a VLAN, the switch may try to switch the copied frames, causing high CPU. The correct answer is that the destination port is not configured as a SPAN destination-only port; it is still a member of a VLAN, causing the switch to process the copied frames as normal traffic.

Key principle: A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.

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 SPAN session is capturing both directions, which doubles the number of packets and increases CPU usage.
Why it's wrong here
Incorrect; capturing both directions is normal and should not cause excessive CPU if the traffic volume is not high.
✗
The destination port is not configured with 'switchport nonegotiate' and is still participating in DTP, causing CPU overhead.
Why it's wrong here
Incorrect; DTP is not related to SPAN CPU usage.
✓
The destination port is still a member of a VLAN, and the switch is processing the copied frames as normal traffic, leading to high CPU.
Why this is correct
Correct; when a destination port is not dedicated to SPAN, the switch may attempt to switch the copied frames, increasing CPU load.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Access ports place end devices into a single VLAN.
✗
The source interface is a trunk port, and SPAN is capturing all VLANs, causing high CPU.
Why it's wrong here
Incorrect; the scenario does not mention trunk, and even if it were, it would not necessarily cause high CPU unless the traffic volume is high.

Common exam traps

Common exam trap: an active trunk can still block the VLAN you need

A trunk being up does not prove every VLAN is crossing it. Check allowed VLAN lists, native VLAN mismatch, VLAN existence and access-port assignment.

Trap categories for this question

Scenario analysis trap
Incorrect; the scenario does not mention trunk, and even if it were, it would not necessarily cause high CPU unless the traffic volume is high.

Detailed technical explanation

How to think about this question

VLAN questions usually combine access-port and trunking clues. The key is to identify whether the issue is local to one switchport, caused by the trunk, or caused by the VLAN not existing where it needs to exist.

KKey Concepts to Remember

Access ports place end devices into a single VLAN.
Trunk ports carry multiple VLANs between switches.
Allowed VLAN lists decide which VLANs can cross a trunk.
Native VLAN mismatch can create confusing symptoms.

TExam Day Tips

Use show vlan brief to verify access VLANs.
Use show interfaces trunk to verify trunk state and allowed VLANs.
Do not treat every same-VLAN issue as a routing problem.

Key takeaway

A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.

Real-world example

How this comes up in practice

A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.

What to study next

Got this wrong? Here's your next step.

Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 350-401 questions on switching, trunking, and access-port configuration.

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FAQ

Questions learners often ask

What does this 350-401 question test?

SPAN and RSPAN — This question tests SPAN and RSPAN — Access ports place end devices into a single VLAN..

What is the correct answer to this question?

The correct answer is: The destination port is still a member of a VLAN, and the switch is processing the copied frames as normal traffic, leading to high CPU. — SPAN can cause high CPU if the destination port is not configured with 'ingress' or if the switch is overloaded. However, a common cause is that the destination port is configured to also forward traffic normally (i.e., it is not a dedicated SPAN destination). But the question says the monitoring station receives traffic, so the destination port is working. High CPU can occur if the SPAN session is configured to capture from a large number of sources or if the switch is processing many packets. The most likely cause here is that the destination port is not configured with 'switchport nonegotiate' or is in a VLAN that causes the switch to process the copied frames as normal traffic, leading to high CPU. But the best answer: The destination port should be configured as a SPAN destination only, and if it is also a member of a VLAN, the switch may try to switch the copied frames, causing high CPU. The correct answer is that the destination port is not configured as a SPAN destination-only port; it is still a member of a VLAN, causing the switch to process the copied frames as normal traffic.

What should I do if I get this 350-401 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?

Access ports place end devices into a single VLAN.

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Last reviewed: Jun 18, 2026

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