Quick Answer
The correct answer is Q-in-Q (802.1ad), which is the encapsulation technology commonly used in service provider networks to separate subscriber traffic in an Ethernet aggregation network. This works by stacking an outer service provider VLAN tag on top of the customer’s inner 802.1Q tag, effectively creating a two-layer VLAN hierarchy that isolates each subscriber’s traffic within a single physical link. On the Cisco SPCOR / CCNP Service Provider Core 350-501 exam, this concept tests your understanding of Ethernet aggregation and subscriber separation, often appearing in questions that contrast Q-in-Q with single-tag 802.1Q or overlay technologies like VXLAN. A common trap is confusing Q-in-Q with MPLS, but remember that Q-in-Q operates at Layer 2 for Ethernet access, while MPLS is a Layer 2.5 label-switching mechanism. Memory tip: think of Q-in-Q as “double-decker” VLANs—one tag for the customer, one for the provider—keeping each subscriber’s traffic in its own lane.
This 350-501 practice question tests your understanding of architecture. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 encapsulation technology is commonly used in service provider networks to separate subscriber traffic in an Ethernet aggregation network?
Q-in-Q (802.1ad)
Double tagging separates subscriber from service VLAN.
VXLAN
Why wrong: VXLAN is overlay; not typical in aggregation.
802.1Q
Why wrong: Single tag, not enough for subscriber separation.
MPLS
Why wrong: MPLS is not an Ethernet encapsulation for subscribers.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Q-in-Q (802.1ad)
Option B is correct because Q-in-Q (802.1ad) allows service providers to stack VLAN tags and separate subscriber traffic effectively. Option A is wrong because 802.1Q is a single VLAN tag. Option C is wrong because VXLAN is used in overlay networks, not typically in aggregation. Option D is wrong because MPLS is not an encapsulation for Ethernet subscriber separation.
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
For each option: why learners choose it and why it is or isn't the right answer here.
Q-in-Q (802.1ad)
VXLAN
Why it's wrong here
VXLAN is overlay; not typical in aggregation.
802.1Q
Why it's wrong here
Single tag, not enough for subscriber separation.
MPLS
Why it's wrong here
MPLS is not an Ethernet encapsulation for subscribers.
Common exam traps
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
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.
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
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
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 350-501 questions on switching, trunking, and access-port configuration.
Architecture — study guide chapter
Learn the concepts, then practise the questions
Architecture practice questions
Targeted practice on this topic area only
All 350-501 questions
500 questions across all exam domains
Cisco SPCOR / CCNP Service Provider Core 350-501 study guide
Full concept coverage aligned to exam objectives
350-501 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Practise 350-501 questions linked to Architecture.
Practise 350-501 questions linked to Networking.
Practise 350-501 questions linked to MPLS and Segment Routing.
Practise 350-501 questions linked to Automation and Quality of Service.
Practise 350-501 questions linked to Services.
Practise 350-501 questions linked to Automation and Assurance.
Practise 350-501 questions linked to 350-501 fundamentals.
Practise 350-501 questions linked to 350-501 scenario.
Practise 350-501 questions linked to 350-501 troubleshooting.
Practice this exam
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
Architecture — This question tests Architecture — Access ports place end devices into a single VLAN..
The correct answer is: Q-in-Q (802.1ad) — Option B is correct because Q-in-Q (802.1ad) allows service providers to stack VLAN tags and separate subscriber traffic effectively. Option A is wrong because 802.1Q is a single VLAN tag. Option C is wrong because VXLAN is used in overlay networks, not typically in aggregation. Option D is wrong because MPLS is not an encapsulation for Ethernet subscriber separation.
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 350-501 questions on switching, trunking, and access-port configuration.
Access ports place end devices into a single VLAN.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Last reviewed: Jun 24, 2026
This 350-501 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-501 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.