The purpose of the encapsulation replicate keyword in a SPAN destination configuration is to preserve the original VLAN tag of mirrored frames. This keyword is critical because, by default, a SPAN destination port strips the VLAN tag from mirrored traffic, sending only untagged frames; encapsulation replicate overrides that behavior by instructing the switch to copy the exact 802.1Q tag from the source interface onto the mirrored packets. On the ENCOR 350-401 exam, this concept tests your understanding of how SPAN handles trunk traffic versus access traffic—a common trap is assuming all mirrored traffic is untagged, when in fact trunk monitoring requires encapsulation replicate to keep VLAN identity intact for accurate analysis. The search intent behind “encapsulation replicate purpose” often arises when candidates confuse it with the “dot1q” keyword, but remember: replicate copies the original tag, while dot1q forces a specific tag. A simple memory tip is “replicate = repeat the tag,” so if you need to see the exact VLAN on the analyzer, you must replicate it.
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.
What is the purpose of the 'encapsulation replicate' keyword in a SPAN destination configuration?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
It preserves the original VLAN tag of mirrored frames.
The 'encapsulation replicate' keyword ensures that the mirrored traffic retains its original VLAN tag when sent to the destination port, which is useful for monitoring trunk traffic.
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.
✓
It preserves the original VLAN tag of mirrored frames.
Why this is correct
Without this keyword, the destination port strips the VLAN tag; with it, the tag is preserved.
Related concept
Access ports place end devices into a single VLAN.
✗
It duplicates the mirrored traffic to multiple destination ports.
Why it's wrong here
This is not the function of 'encapsulation replicate'; it deals with VLAN tagging.
✗
It enables RSPAN functionality.
Why it's wrong here
RSPAN uses a different configuration syntax.
✗
It allows the destination port to send traffic as well.
Why it's wrong here
SPAN destination ports are typically in a special state and do not forward normal traffic.
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 350-401 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 350-401 questions on switching, trunking, and access-port configuration.
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: It preserves the original VLAN tag of mirrored frames. — The 'encapsulation replicate' keyword ensures that the mirrored traffic retains its original VLAN tag when sent to the destination port, which is useful for monitoring trunk traffic.
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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