- A
The trunk ports between the switches do not have the RSPAN VLAN (999) in their allowed VLAN list.
Correct; the RSPAN VLAN must be allowed on all trunk links to transport the mirrored traffic to the destination switch.
- B
The destination session on the central switch is configured with 'monitor session 2 destination remote vlan 999' instead of 'monitor session 2 destination interface Gi1/0/1'.
Why wrong: Incorrect; the destination session should use 'destination remote vlan' to receive from the RSPAN VLAN, but the question says the destination session is configured, so this is not the missing piece.
- C
The source sessions on the remote switches are configured with 'monitor session 1 source vlan 100' but the destination is not set to 'remote vlan 999'.
Why wrong: Incorrect; the source session should have 'destination remote vlan 999', but the question states the source sessions are configured, so this is not the missing piece.
- D
The RSPAN VLAN is not created as a remote SPAN VLAN; it must be configured with 'remote-span' command.
Why wrong: Incorrect; the 'remote-span' command is used on the VLAN to designate it as an RSPAN VLAN, but the question says the VLAN is active, implying it is configured. However, this is a common missing step, but the most likely missing configuration is the trunk allowance.
Quick Answer
The answer is that the trunk ports between the switches are missing the RSPAN VLAN (999) in their allowed VLAN list. This is the likely missing configuration because RSPAN relies on a dedicated VLAN to carry mirrored traffic across the network; if that VLAN is not explicitly permitted on every trunk link between the source switches and the central destination switch, the encapsulated monitoring traffic will be dropped at the first trunk interface. On the ENCOR 350-401 exam, this question tests your understanding of RSPAN’s Layer 2 transport requirements, often hiding the trap in a scenario where the RSPAN VLAN is active and sessions are configured, leading you to overlook the trunk’s allowed list. A common memory tip is “RSPAN rides the trunk—if the VLAN isn’t allowed, the ride is stalled.”
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 RSPAN to monitor traffic from multiple switches in a data center. The monitoring station is connected to a central switch. The engineer has configured an RSPAN VLAN (VLAN 999) on all switches and set up the source sessions on the remote switches. However, the monitoring station receives no traffic. On the central switch, the engineer verifies that the RSPAN VLAN is active and that the destination session is configured. What is a likely missing configuration?
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 trunk ports between the switches do not have the RSPAN VLAN (999) in their allowed VLAN list.
For RSPAN to work, the RSPAN VLAN must be allowed on all trunk links between the source switches and the destination switch. If the trunk ports do not have the RSPAN VLAN in their allowed list, the traffic will be dropped. Also, the RSPAN VLAN must not be pruned by VTP. The correct answer is that the trunk ports between the switches are not configured to allow the RSPAN VLAN. Option B is incorrect because the destination session is already configured. Option C is incorrect because the source session is already configured. Option D is incorrect because the RSPAN VLAN is active.
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 trunk ports between the switches do not have the RSPAN VLAN (999) in their allowed VLAN list.
- ✗
The destination session on the central switch is configured with 'monitor session 2 destination remote vlan 999' instead of 'monitor session 2 destination interface Gi1/0/1'.
Why it's wrong here
Incorrect; the destination session should use 'destination remote vlan' to receive from the RSPAN VLAN, but the question says the destination session is configured, so this is not the missing piece.
- ✗
The source sessions on the remote switches are configured with 'monitor session 1 source vlan 100' but the destination is not set to 'remote vlan 999'.
Why it's wrong here
Incorrect; the source session should have 'destination remote vlan 999', but the question states the source sessions are configured, so this is not the missing piece.
- ✗
The RSPAN VLAN is not created as a remote SPAN VLAN; it must be configured with 'remote-span' command.
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
Command / output trap
Incorrect; the 'remote-span' command is used on the VLAN to designate it as an RSPAN VLAN, but the question says the VLAN is active, implying it is configured. However, this is a common missing step, but the most likely missing configuration is the trunk allowance.
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 trunk ports between the switches do not have the RSPAN VLAN (999) in their allowed VLAN list. — For RSPAN to work, the RSPAN VLAN must be allowed on all trunk links between the source switches and the destination switch. If the trunk ports do not have the RSPAN VLAN in their allowed list, the traffic will be dropped. Also, the RSPAN VLAN must not be pruned by VTP. The correct answer is that the trunk ports between the switches are not configured to allow the RSPAN VLAN. Option B is incorrect because the destination session is already configured. Option C is incorrect because the source session is already configured. Option D is incorrect because the RSPAN VLAN is active.
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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