350-501 Architecture Practice Question
Which encapsulation technology is commonly used in service provider networks to separate subscriber traffic in an Ethernet aggregation network?
⚠ Common exam trap
Cisco often tests the distinction between 802.1Q (single tagging) and 802.1ad (Q-in-Q) in aggregation networks, where candidates mistakenly choose 802.1Q because they overlook the need to preserve customer VLANs while scaling beyond 4096 VLANs.
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
✓
Q-in-Q (802.1ad)
Q-in-Q (802.1ad) is the correct encapsulation technology because it allows service providers to stack an outer service VLAN tag (S-Tag) on top of a customer's inner VLAN tag (C-Tag), effectively separating subscriber traffic in an Ethernet aggregation network. This double-tagging mechanism preserves the customer's VLAN space while enabling the provider to aggregate multiple subscribers over a single physical port, which is essential for Metro Ethernet and DSLAM aggregation scenarios.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Q-in-Q (802.1ad)
Why this is correct
Double tagging separates subscriber from service VLAN.
- ✗
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.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.