ISC2 CC Network Security Practice Question
In the OSI model, which layer uses MAC addresses to forward frames and supports VLANs?
⚠ Common exam trap
Many candidates confuse Layer 2 and Layer 3 responsibilities — candidates see 'VLANs' and think routing (Layer 3), but VLAN tagging and MAC-based forwarding are strictly Layer 2 functions.
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
The Data Link layer (Layer 2) is responsible for framing, MAC addressing, and forwarding frames within a local network segment. VLANs (802.1Q) are a Layer 2 construct that logically segments a switch into multiple broadcast domains, and VLAN tags are inserted into Ethernet frames — making Layer 2 the correct answer. Switches use MAC address tables to forward frames and enforce VLAN membership.
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 2 - Data Link
Why this is correct
Layer 2, the Data Link layer, forwards frames using MAC addresses and supports VLANs through 802.1Q tagging, which inserts a VLAN identifier into the Ethernet frame header. This satisfies the stem's requirement for the layer that both addresses frames by MAC and provides VLAN segmentation.
- ✗
Layer 4 - Transport
Why it's wrong here
Layer 4 segments data and identifies applications through port numbers; it forwards segments between hosts, not frames between switch ports, and VLAN membership is not a transport-layer function. It is tempting because TCP and UDP ports are familiar addressing concepts, and Layer 4 would be correct if the question concerned multiplexing or end-to-end delivery.
- ✗
Layer 3 - Network
Why it's wrong here
Layer 3 forwards packets using logical IP addresses and performs routing between subnets; MAC addresses and VLAN tagging belong to Layer 2. It is tempting because Layer 3 switches also support VLANs, but that is a switching feature, and Layer 3 would be correct if the question asked which layer routes between networks.
- ✗
Layer 1 - Physical
Why it's wrong here
Layer 1 carries raw bits over the physical medium and has no concept of frames, MAC addresses or VLAN tags. It is tempting because cabling and interfaces are the tangible foundation of any switched network, and Layer 1 would be correct if the question asked where encoding, signalling or media types are defined.
Visual reference
Quick reference
Access Control Model Comparison
| Model | Acronym | Who Controls Access? | Best For |
|---|---|---|---|
| Discretionary Access Control | DAC | Resource owner | Small teams, file shares |
| Mandatory Access Control | MAC | System / security labels | Classified govt / military |
| Role-Based Access Control | RBAC | Administrator (via roles) | Enterprise environments |
| Attribute-Based Access Control | ABAC | Policy engine (user + resource attributes) | Fine-grained, dynamic policies |
| Rule-Based Access Control | RuBAC | System rules / ACLs | Firewall rules, network ACLs |
Go deeper
Related to this question
Learn chapter
Network Security Foundations
Key term
MAC
MAC (Media Access Control) is a unique hardware identifier assigned to network interfaces for communication on a local network segment.
Key term
VLAN
A VLAN (Virtual Local Area Network) is a logical grouping of network devices that behave as if they are on the same physical network segment, regardless of their actual physical location.
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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 ISC2 exam blueprint
This CC practice question is part of Courseiva's free ISC2 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 CC exam.