- A
Configure 'monitor session 1 source interface Gi1/0/1 both' and 'monitor session 1 destination interface Gi1/0/24'.
Why wrong: Incorrect; this would only capture traffic on that specific interface, not all inter-VLAN traffic.
- B
Configure 'monitor session 1 source vlan 10 - 20 both' and 'monitor session 1 destination interface Gi1/0/24'.
Correct; VLAN-based SPAN captures all traffic entering or leaving the specified VLANs, including routed traffic between them.
- C
Configure an RSPAN VLAN and use 'monitor session 1 source vlan 10 - 20' and 'monitor session 1 destination remote vlan 100'.
Why wrong: Incorrect; RSPAN is used when the monitoring station is on a different switch; here it is local.
- D
Configure an ERSPAN session with source IP and destination IP.
Why wrong: Incorrect; ERSPAN is for encapsulating traffic over IP, not necessary for local capture.
Quick Answer
The answer is to configure 'monitor session 1 source vlan 10 - 20 both' with 'monitor session 1 destination interface Gi1/0/24'. This is correct because inter-VLAN traffic is routed by the switch’s Layer 3 engine, meaning it never appears as ingress or egress on a single physical port; instead, it traverses the VLANs themselves via the SVI. VLAN-based SPAN captures all packets entering or leaving the specified VLANs, including the routed traffic between them, which is exactly what you need for inter-VLAN traffic capture with VLAN SPAN. On the ENCOR 350-401 exam, this question tests your understanding that interface SPAN only mirrors a specific port’s traffic, missing routed frames, while RSPAN and ERSPAN are overkill for a local monitoring station. A common trap is choosing interface SPAN on the SVI or a trunk port, but that won’t capture the full routed flow. Memory tip: think “VLAN SPAN for VLAN traffic” — if the traffic crosses VLANs, source the VLANs, not the ports.
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.
A network engineer needs to monitor traffic between two VLANs on a Cisco Catalyst 9300 switch. The engineer wants to capture all packets that traverse the switch between VLAN 10 and VLAN 20. The monitoring station is connected to port Gi1/0/24. Which configuration should the engineer use to capture this inter-VLAN traffic?
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 vlan 10 - 20 both' and 'monitor session 1 destination interface Gi1/0/24'.
Inter-VLAN traffic is routed by the switch's Layer 3 engine. To capture it, the engineer must use a SPAN session that sources from the VLANs themselves (VLAN-based SPAN) or from the SVI. The correct answer is to configure a SPAN session with source VLANs 10 and 20, and destination interface Gi1/0/24. This captures all traffic entering or leaving those VLANs, including routed traffic. Option A is incorrect because interface SPAN would only capture traffic on that specific port, not all inter-VLAN traffic. Option C is incorrect because RSPAN is for remote monitoring, not needed here. Option D is incorrect because ERSPAN is for encapsulated remote SPAN over IP, not needed.
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 destination interface Gi1/0/24'.
Why it's wrong here
Incorrect; this would only capture traffic on that specific interface, not all inter-VLAN traffic.
- ✓
Configure 'monitor session 1 source vlan 10 - 20 both' and 'monitor session 1 destination interface Gi1/0/24'.
- ✗
Configure an RSPAN VLAN and use 'monitor session 1 source vlan 10 - 20' and 'monitor session 1 destination remote vlan 100'.
Why it's wrong here
Incorrect; RSPAN is used when the monitoring station is on a different switch; here it is local.
- ✗
Configure an ERSPAN session with source IP and destination IP.
Why it's wrong here
Incorrect; ERSPAN is for encapsulating traffic over IP, not necessary for local capture.
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 vlan 10 - 20 both' and 'monitor session 1 destination interface Gi1/0/24'. — Inter-VLAN traffic is routed by the switch's Layer 3 engine. To capture it, the engineer must use a SPAN session that sources from the VLANs themselves (VLAN-based SPAN) or from the SVI. The correct answer is to configure a SPAN session with source VLANs 10 and 20, and destination interface Gi1/0/24. This captures all traffic entering or leaving those VLANs, including routed traffic. Option A is incorrect because interface SPAN would only capture traffic on that specific port, not all inter-VLAN traffic. Option C is incorrect because RSPAN is for remote monitoring, not needed here. Option D is incorrect because ERSPAN is for encapsulated remote SPAN over IP, not needed.
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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