Which layer does 802.1Q tagging operate at?

• A. Layer 3
• B. Layer 2
• C. Layer 1
• D. Layer 4

Answer: (B)

802.1Q tagging operates at Layer 2, the Data Link layer. This tagging concerns how Ethernet frames are forwarded within a local network and how switches separate traffic into different VLANs. The tag is inserted into the frame header (between the source MAC address and the EtherType field) to carry the VLAN ID (and optional priority), enabling switches to keep broadcast domains distinct. Layer 3 handles routing between networks (IP addressing), Layer 1 covers the physical signaling, and Layer 4 deals with transport protocols like TCP/UDP. So the tagging decision and the VLAN segmentation are inherently a Layer 2 function.