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SPAN and RSPAN →mediumMultiple ChoiceObjective-mapped

Quick Answer

The correct configuration is to use the `monitor session 1 source interface Gi1/0/1 both` command followed by `monitor session 1 filter vlan 20`, because the `filter vlan` option is the only way to restrict a SPAN session to capture traffic from a specific VLAN on a trunk port without affecting the source interface’s operation. This works by applying an ingress and egress VLAN filter to the monitored traffic, ensuring that only frames tagged with VLAN 20 are copied to the destination port. On the ENCOR 350-401 exam, this concept tests your understanding of SPAN filtering versus VLAN-based SPAN, a common trap where candidates mistakenly use `monitor session source vlan`—which captures all traffic on that VLAN across the entire switch, not just from the trunk. Remember the key distinction: `filter vlan` narrows the source interface’s traffic, while `source vlan` broadens it to all ports. A useful memory tip is “Filter the trunk, source the VLAN” to avoid confusing the two commands.

350-401 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.

An engineer is configuring SPAN on a Cisco Catalyst 3850 switch to monitor traffic from a trunk port (Gi1/0/1) that carries VLANs 10, 20, and 30. The monitoring station is on port Gi1/0/24. The engineer wants to capture only VLAN 20 traffic from the trunk. Which configuration should the engineer use?

Question 1mediummultiple choice
Open the full VLAN trunking answer →

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

✓

Configure 'monitor session 1 source interface Gi1/0/1 both' and 'monitor session 1 filter vlan 20'.

To capture traffic from a specific VLAN on a trunk port, the engineer must use the 'filter vlan' option in the SPAN session. The correct answer is to configure 'monitor session 1 source interface Gi1/0/1 both' and then 'monitor session 1 filter vlan 20'. Option B is incorrect because it captures all VLANs. Option C is incorrect because VLAN-based SPAN would capture all traffic on VLAN 20 from all ports, not just the trunk. Option D is incorrect because it captures only VLAN 20 but from all ports.

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.

  • ✓

    Configure 'monitor session 1 source interface Gi1/0/1 both' and 'monitor session 1 filter vlan 20'.

    Why this is correct

    Correct; the filter vlan option limits the SPAN session to only VLAN 20 traffic on the source interface.

    Related concept

    Access ports place end devices into a single VLAN.

  • ✗

    Configure 'monitor session 1 source interface Gi1/0/1 both' and 'monitor session 1 destination interface Gi1/0/24'.

    Why it's wrong here

    Incorrect; this would capture all VLANs on the trunk, not just VLAN 20.

  • ✗

    Configure 'monitor session 1 source vlan 20' and 'monitor session 1 destination interface Gi1/0/24'.

    Why it's wrong here

    Incorrect; this would capture all traffic on VLAN 20 from all ports, not just the trunk port.

  • ✗

    Configure 'monitor session 1 source interface Gi1/0/1 both' and 'monitor session 1 filter vlan 10,30'.

    Why it's wrong here

    Incorrect; this would filter out VLANs 10 and 30, but the filter is applied to the source, and the syntax is 'filter vlan' with the VLANs to include, not exclude.

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.

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: Configure 'monitor session 1 source interface Gi1/0/1 both' and 'monitor session 1 filter vlan 20'. — To capture traffic from a specific VLAN on a trunk port, the engineer must use the 'filter vlan' option in the SPAN session. The correct answer is to configure 'monitor session 1 source interface Gi1/0/1 both' and then 'monitor session 1 filter vlan 20'. Option B is incorrect because it captures all VLANs. Option C is incorrect because VLAN-based SPAN would capture all traffic on VLAN 20 from all ports, not just the trunk. Option D is incorrect because it captures only VLAN 20 but from all ports.

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

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.

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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This 350-401 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 350-401 exam.