Question 1,893 of 2,015

SPAN and RSPAN →mediumMultiple SelectObjective-mapped

Quick Answer

The correct answer is that a SPAN destination port cannot be used for normal network traffic. This is because when a port is configured as a SPAN destination, it is placed into a special monitoring mode that strips it of its normal switching functionality—it can only receive copied frames from the source ports and cannot forward or receive standard data traffic. On the ENCOR 350-401 exam, this concept tests your understanding of how SPAN and RSPAN limitations affect network design, often appearing in a "choose three" format where common traps include assuming RSPAN supports Layer 3 source interfaces directly or that SPAN can monitor control plane traffic without special configuration. Remember that SPAN impacts CPU performance, RSPAN requires a dedicated VLAN pruned across the network, and neither allows the destination port to function as a regular switchport. A useful memory tip: "Destination is dead to data"—once a port is a SPAN destination, it stops normal switching.

350-401 SPAN and RSPAN Practice Question

This 350-401 practice question tests your understanding of span and rspan. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.

Which three statements about SPAN and RSPAN limitations are true? (Choose three.)

Question 1mediummulti select

Full question →

A
SPAN can cause increased CPU utilization on the switch if many packets are mirrored.
Correct because mirroring high-bandwidth traffic can stress the switch CPU.
B
SPAN can monitor control plane traffic such as routing protocol updates by default.
Why wrong: Incorrect because SPAN typically monitors only data plane traffic; control plane traffic is not mirrored unless using CPU SPAN or special configuration.
C
RSPAN requires that the RSPAN VLAN be pruned from all trunks to avoid loops.
Correct because the RSPAN VLAN should be pruned from trunks where it is not needed to prevent loops and unnecessary flooding.
D
A SPAN destination port cannot be used for normal network traffic.
Correct because the destination port is dedicated to receiving mirrored traffic and does not forward normal traffic.
E
RSPAN can be used to monitor traffic on a Layer 3 routed interface.
Why wrong: Incorrect because RSPAN sources must be Layer 2 interfaces; Layer 3 interfaces are not supported as RSPAN sources.

Full breakdown with real-world context →

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

✓

SPAN can cause increased CPU utilization on the switch if many packets are mirrored.

SPAN and RSPAN can impact switch performance due to increased CPU/memory usage. SPAN cannot monitor control plane traffic (e.g., routing updates) unless specifically configured. RSPAN requires a dedicated VLAN that must be pruned appropriately. A SPAN destination port stops normal switching. RSPAN does not support Layer 3 routed interfaces as sources directly.

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.

✓
SPAN can cause increased CPU utilization on the switch if many packets are mirrored.
Why this is correct
Correct because mirroring high-bandwidth traffic can stress the switch CPU.
Related concept
Access ports place end devices into a single VLAN.
✗
SPAN can monitor control plane traffic such as routing protocol updates by default.
Why it's wrong here
Incorrect because SPAN typically monitors only data plane traffic; control plane traffic is not mirrored unless using CPU SPAN or special configuration.
✓
RSPAN requires that the RSPAN VLAN be pruned from all trunks to avoid loops.
Why this is correct
Correct because the RSPAN VLAN should be pruned from trunks where it is not needed to prevent loops and unnecessary flooding.
Related concept
Access ports place end devices into a single VLAN.
✓
A SPAN destination port cannot be used for normal network traffic.
Why this is correct
Correct because the destination port is dedicated to receiving mirrored traffic and does not forward normal traffic.
Related concept
Access ports place end devices into a single VLAN.
✗
RSPAN can be used to monitor traffic on a Layer 3 routed interface.
Why it's wrong here
Incorrect because RSPAN sources must be Layer 2 interfaces; Layer 3 interfaces are not supported as RSPAN sources.

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: SPAN can cause increased CPU utilization on the switch if many packets are mirrored. — SPAN and RSPAN can impact switch performance due to increased CPU/memory usage. SPAN cannot monitor control plane traffic (e.g., routing updates) unless specifically configured. RSPAN requires a dedicated VLAN that must be pruned appropriately. A SPAN destination port stops normal switching. RSPAN does not support Layer 3 routed interfaces as sources directly.

What should I do if I get this 350-401 question wrong?

What is the key concept behind this question?

Access ports place end devices into a single VLAN.

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