The answer is that the RSPAN VLAN native VLAN conflict causes intermittent traffic because the RSPAN VLAN 200 is also configured as the native VLAN on some trunk links. When the RSPAN VLAN doubles as the native VLAN, mirrored frames that should be tagged with VLAN 200 are instead sent untagged across the trunk, leading the receiving switch to misinterpret them as belonging to the default native VLAN rather than the RSPAN VLAN, which can result in dropped or misdirected packets. This scenario tests your understanding of how RSPAN traffic must remain tagged to traverse the network correctly, a key concept for the Cisco CCNP ENARSI 300-410 exam where the common trap is assuming any VLAN works for RSPAN without considering native VLAN interactions. A useful memory tip is: "RSPAN tags its traffic; a native VLAN strips the tag—never let them be the same."
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.
A switch is configured with RSPAN to monitor traffic from VLAN 50 to a remote switch via VLAN 200. The source switch has: monitor session 1 source vlan 50 rx monitor session 1 destination remote vlan 200. The remote switch has: monitor session 2 source remote vlan 200 monitor session 2 destination interface Gi0/2. The intermediate switches have VLAN 200 configured with 'remote-span'. The network uses VTP transparent mode. The analyzer connected to Gi0/2 sees intermittent traffic. The RSPAN VLAN 200 is also used as a native VLAN on some trunk ports. What is the likely cause of intermittent traffic?
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 200 is also the native VLAN on some trunks, causing the mirrored frames to be sent untagged and possibly dropped.
RSPAN traffic is flooded across the RSPAN VLAN. If the RSPAN VLAN is used as the native VLAN on trunk ports, the switch may treat the RSPAN frames as untagged. However, RSPAN expects the frames to be tagged with the RSPAN VLAN ID. When the native VLAN is the same as the RSPAN VLAN, the frames may be sent untagged on the trunk, but the receiving switch may interpret them as belonging to the native VLAN, causing them to be dropped or misdirected. This can lead to intermittent loss because the native VLAN handling may vary. The correct fix is to ensure the RSPAN VLAN is not the native VLAN on any trunk.
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 200 is also the native VLAN on some trunks, causing the mirrored frames to be sent untagged and possibly dropped.
Why this is correct
When the RSPAN VLAN is the native VLAN, frames are sent untagged, but the receiving switch expects tagged frames for the RSPAN VLAN.
Related concept
Access ports place end devices into a single VLAN.
✗
VTP transparent mode prevents RSPAN from working correctly.
Why it's wrong here
VTP transparent mode is fine for RSPAN.
✗
The source VLAN 50 is not allowed on the trunk ports.
Why it's wrong here
The RSPAN VLAN is used for mirroring, not the source VLAN.
✗
The monitor session 2 is missing the 'no shutdown' command.
Why it's wrong here
SPAN sessions are enabled by default.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
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.
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 200 is also the native VLAN on some trunks, causing the mirrored frames to be sent untagged and possibly dropped. — RSPAN traffic is flooded across the RSPAN VLAN. If the RSPAN VLAN is used as the native VLAN on trunk ports, the switch may treat the RSPAN frames as untagged. However, RSPAN expects the frames to be tagged with the RSPAN VLAN ID. When the native VLAN is the same as the RSPAN VLAN, the frames may be sent untagged on the trunk, but the receiving switch may interpret them as belonging to the native VLAN, causing them to be dropped or misdirected. This can lead to intermittent loss because the native VLAN handling may vary. The correct fix is to ensure the RSPAN VLAN is not the native VLAN on any trunk.
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.
What is the key concept behind this question?
Access ports place end devices into a single VLAN.
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