200-901 Network Fundamentals Practice Question
A network administrator configures a switch port to belong to VLAN 10. Which OSI layer is primarily involved in VLAN tagging?
⚠ Common exam trap
200-901 often tests the OSI layer of common protocols — candidates sometimes confuse VLAN tagging with Layer 3 because VLANs are often used for subnetting, but tagging itself is strictly Layer 2.
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
✓
Layer 2 (Data Link)
VLAN tagging is defined in IEEE 802.1Q, which operates at Layer 2 (Data Link) of the OSI model. The 802.1Q tag is inserted into the Ethernet frame header, and switches use this tag to make forwarding decisions within the same broadcast domain. Therefore, VLAN tagging is primarily a Layer 2 function.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Layer 1 (Physical)
Why it's wrong here
Tagging modifies the Ethernet frame header, a Layer 2 construct, whereas Layer 1 carries only raw bits and signalling without frame fields. It tempts because VLANs map to physical switch ports, but the port's membership is logical, and the tag is added at the data-link layer.
- ✗
Layer 3 (Network)
Why it's wrong here
VLAN tags sit in the Ethernet frame header, which is Layer 2, so Layer 3 never encapsulates them; routing between VLANs is where Layer 3 applies. It tempts because IP addressing is commonly associated with VLAN subnets, but tagging itself is switched, not routed.
- ✓
Layer 2 (Data Link)
Why this is correct
VLAN tagging inserts 802.1Q tags into Ethernet frames, which are Layer 2 constructs. The switch examines these tags to segregate broadcast domains, so VLAN membership is determined at the Data Link layer rather than Layer 3.
- ✗
Layer 4 (Transport)
Why it's wrong here
VLAN tags are inserted into the Layer 2 Ethernet frame, not into TCP or UDP headers, so Layer 4 plays no part in tagging. It tempts because transport-layer ports are often filtered per VLAN, yet that is policy applied to traffic, not the tagging mechanism itself.
Visual reference
Go deeper
Related to this question
About these practice questions
This 200-901 question is part of Courseiva's 975-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
This 200-901 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 200-901 exam.