The answer is that RSPAN traffic traverses the stack ring, which is disrupted during master re-election. In a switch stack, the stack ring serves as the backplane for inter-member communication, and RSPAN mirrored packets must cross this ring to reach a destination port on a different member. When a stack master re-election occurs, the ring briefly goes down or reconverges as the new master is elected, causing intermittent gaps in the mirrored traffic. This concept tests your understanding of how control-plane events impact data-plane forwarding in a stacked environment, a common scenario on the Cisco CCNP ENARSI 300-410 exam. A frequent trap is assuming RSPAN is purely local to a single switch, but the key is that any inter-member traffic relies on the stack ring’s stability. Remember: RSPAN across the stack means the ring must stay intact—master re-election breaks the link.
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 on a switch stack to monitor traffic from a VLAN. The RSPAN destination port is on a different stack member. The mirrored traffic works intermittently, with gaps during stack master re-election. What is the most likely explanation?
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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
RSPAN traffic traverses the stack ring, which is disrupted during master re-election.
In a switch stack, RSPAN traffic is forwarded across the stack ring. During master re-election, the stack ring may briefly go down or reconverge, causing loss of RSPAN traffic. Additionally, if the RSPAN VLAN is not configured consistently across all stack members, traffic may be dropped.
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.
✓
RSPAN traffic traverses the stack ring, which is disrupted during master re-election.
Why this is correct
The stack ring is used for inter-member communication; a master change can cause temporary disruption.
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 pruned on the stack ring due to VTP pruning.
Why it's wrong here
VTP pruning is not typically enabled on stack rings, and the issue is intermittent.
✗
The RSPAN session is configured on the master only, and does not survive failover.
Why it's wrong here
RSPAN sessions are replicated to all stack members; they persist across failover.
✗
The destination port is on a different VLAN than the source, causing a mismatch.
Why it's wrong here
RSPAN uses a dedicated VLAN; the destination port is in that VLAN, not the source 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.
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: RSPAN traffic traverses the stack ring, which is disrupted during master re-election. — In a switch stack, RSPAN traffic is forwarded across the stack ring. During master re-election, the stack ring may briefly go down or reconverge, causing loss of RSPAN traffic. Additionally, if the RSPAN VLAN is not configured consistently across all stack members, traffic may be dropped.
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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