The answer is that the SPAN session is capturing only ingress traffic because the default direction for a SPAN source is ingress only. By default, when you configure a SPAN source using the `monitor session source` command without specifying a direction, the switch applies the `rx` keyword, meaning it only copies packets received on that source interface or VLAN. This explains why the laptop sees only traffic generated by the switch itself—those packets are entering the switch’s monitoring port—while traffic from other devices in VLAN 20, which would be forwarded out of the switch, is not captured. On the Cisco CCNP ENARSI 300-410 exam, this is a classic trap: candidates often assume SPAN captures all traffic by default, but the default direction is ingress only. To capture both directions, you must explicitly add the `both` keyword to the source configuration. A quick memory tip: think “SPAN defaults to RX” as in “receive only”—if you want both ways, you have to say so.
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 a local SPAN session on a Cisco switch to monitor all traffic on VLAN 20. The engineer uses the command 'monitor session 1 source vlan 20' and 'monitor session 1 destination interface GigabitEthernet0/3'. The engineer connects a laptop to GigabitEthernet0/3 and runs a packet capture, but sees only traffic from the switch itself, not from other devices in VLAN 20. 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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The SPAN session is configured to monitor only ingress traffic by default.
By default, SPAN monitors only ingress traffic on the source VLAN. To capture both directions, the command must specify 'both' for the source. The default is 'rx' only.
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 SPAN session is configured to monitor only ingress traffic by default.
Why this is correct
Correct because the default direction for a SPAN source VLAN is 'rx' (received traffic); to capture all traffic, the engineer must add 'both' or 'tx'.
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 destination port is in a different VLAN than the source VLAN.
Why it's wrong here
Incorrect because the destination port does not need to be in the same VLAN; it receives a copy of the traffic regardless.
✗
The switch does not support SPAN on VLANs.
Why it's wrong here
Incorrect because most Cisco switches support SPAN on VLANs; this is a common feature.
✗
The laptop is not configured to accept tagged traffic.
Why it's wrong here
Incorrect because SPAN sends untagged copies of traffic to the destination port by default; tagging is not required.
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 SPAN session is configured to monitor only ingress traffic by default. — By default, SPAN monitors only ingress traffic on the source VLAN. To capture both directions, the command must specify 'both' for the source. The default is 'rx' only.
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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