350-501 Architecture Practice Question
In an MPLS-based service provider core network, the aggregation layer typically connects to the core backbone. Which technology is primarily used at the aggregation layer to scale Ethernet services for many customers while preserving VLAN separation?
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 (IEEE 802.1ad)
Q-in-Q (802.1ad) allows service providers to stack a customer VLAN tag on top of a service VLAN tag, enabling scalable customer separation in metro Ethernet networks.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
IEEE 802.1ah (MAC-in-MAC)
Why it's wrong here
MAC-in-MAC is used for provider backbone bridging, not typical for simple double tagging.
- ✗
IEEE 802.3ad (Link Aggregation)
Why it's wrong here
Link aggregation bundles links, does not scale VLANs.
- ✗
IEEE 802.1x (Port-based Network Access Control)
Why it's wrong here
802.1x is for authentication, not VLAN scaling.
- ✓
Q-in-Q (IEEE 802.1ad)
Why this is correct
Q-in-Q double-tags Ethernet frames to scale VLANs per customer.
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