- A
The RSPAN VLAN is not allowed on a trunk link between the source and destination switches.
RSPAN traffic traverses the network in the RSPAN VLAN; if that VLAN is not permitted on an intermediate trunk, the traffic is dropped.
- B
The RSPAN VLAN is configured as a native VLAN on the trunk, causing VLAN tagging issues.
Why wrong: RSPAN VLANs can be native, but the native VLAN is untagged; RSPAN expects tagged frames unless configured otherwise.
- C
The destination switch has a different RSPAN VLAN ID configured for the session.
Why wrong: The RSPAN VLAN must match on both switches; a mismatch would prevent the destination from recognizing the traffic.
- D
The source switch has not enabled RSPAN globally with the 'monitor session' command.
Why wrong: RSPAN is configured per session, not globally; the session configuration creates the RSPAN VLAN.
300-410 SPAN, RSPAN, and ERSPAN Practice Question
This 300-410 practice question tests your understanding of span, rspan, and erspan. 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 configures RSPAN VLAN 100 on two switches to monitor traffic across the network. The remote switch shows the RSPAN source as active, but the destination switch receives no mirrored traffic. 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.
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 RSPAN VLAN is not allowed on a trunk link between the source and destination switches.
RSPAN requires that the RSPAN VLAN be created and allowed on all intermediate switches (trunks) between source and destination. If the RSPAN VLAN is pruned or not allowed on a trunk, the mirrored traffic never reaches the destination. Additionally, the RSPAN VLAN must not be used for user data.
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 RSPAN VLAN is not allowed on a trunk link between the source and destination switches.
Why this is correct
RSPAN traffic traverses the network in the RSPAN VLAN; if that VLAN is not permitted on an intermediate trunk, the traffic is dropped.
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 RSPAN VLAN is configured as a native VLAN on the trunk, causing VLAN tagging issues.
Why it's wrong here
RSPAN VLANs can be native, but the native VLAN is untagged; RSPAN expects tagged frames unless configured otherwise.
- ✗
The destination switch has a different RSPAN VLAN ID configured for the session.
Why it's wrong here
The RSPAN VLAN must match on both switches; a mismatch would prevent the destination from recognizing the traffic.
- ✗
The source switch has not enabled RSPAN globally with the 'monitor session' command.
Why it's wrong here
RSPAN is configured per session, not globally; the session configuration creates the RSPAN VLAN.
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 300-410 questions on switching, trunking, and access-port configuration.
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FAQ
Questions learners often ask
What does this 300-410 question test?
SPAN, RSPAN, and ERSPAN — This question tests SPAN, RSPAN, and ERSPAN — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: The RSPAN VLAN is not allowed on a trunk link between the source and destination switches. — RSPAN requires that the RSPAN VLAN be created and allowed on all intermediate switches (trunks) between source and destination. If the RSPAN VLAN is pruned or not allowed on a trunk, the mirrored traffic never reaches the destination. Additionally, the RSPAN VLAN must not be used for user data.
What should I do if I get this 300-410 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 300-410 questions on switching, trunking, and access-port configuration.
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 19, 2026
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