The answer is that SPAN must be configured on the port-channel interface, not on the individual physical interface. When you configure a SPAN source using a physical interface that is part of an EtherChannel, the switch only monitors traffic on that specific physical link, not the aggregated bandwidth of the entire EtherChannel. This causes only half the traffic—either incoming or outgoing on that single member link—to be mirrored to the analyzer, rather than the full bidirectional traffic of the port-channel. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of how SPAN interacts with EtherChannel, a common trap where candidates mistakenly target a physical interface instead of the logical port-channel. Remember the memory tip: “Mirror the bundle, not the wire”—always use the port-channel interface as the SPAN source to capture all traffic across the EtherChannel.
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 SPAN to monitor traffic on interface Gi0/0/0 to a local analyzer on interface Gi0/1. The configuration: monitor session 1 source interface Gi0/0/0 both monitor session 1 destination interface Gi0/1. The analyzer sees only half of the traffic (only incoming or outgoing). The switch also has an EtherChannel configured on Gi0/0/0 as part of a port-channel. The port-channel is up/up. What is the root cause?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The SPAN source is a physical interface that is part of an EtherChannel; SPAN should be configured on the port-channel interface instead.
When a source interface is part of an EtherChannel, SPAN must be configured on the port-channel interface, not on the individual physical interface. If SPAN is configured on a physical interface that is part of a port-channel, the switch may only monitor traffic on that specific physical link, not the entire EtherChannel. This can result in only a portion of the traffic being mirrored. The fix is to use the port-channel interface as the source.
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 source is a physical interface that is part of an EtherChannel; SPAN should be configured on the port-channel interface instead.
Why this is correct
SPAN on a physical member of an EtherChannel only monitors that link, not the entire bundle.
Related concept
Access ports place end devices into a single VLAN.
✗
The destination interface Gi0/1 is not in the same VLAN as the source.
Why it's wrong here
SPAN does not require VLAN matching; it sends mirrored traffic regardless.
✗
The monitor session is missing the 'no shutdown' command.
Why it's wrong here
SPAN sessions are enabled by default.
✗
The EtherChannel load-balancing algorithm causes some traffic to be missed.
Why it's wrong here
The issue is not load-balancing but the source interface selection.
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 source is a physical interface that is part of an EtherChannel; SPAN should be configured on the port-channel interface instead. — When a source interface is part of an EtherChannel, SPAN must be configured on the port-channel interface, not on the individual physical interface. If SPAN is configured on a physical interface that is part of a port-channel, the switch may only monitor traffic on that specific physical link, not the entire EtherChannel. This can result in only a portion of the traffic being mirrored. The fix is to use the port-channel interface as the source.
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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