IEEE 802.1Q defines VLAN Tagging.

• A. IP Tagging
• B. Frame Tagging
• C. VLAN Tagging
• D. Port Tagging

Answer: (C)

VLAN tagging is the mechanism defined by IEEE 802.1Q to mark Ethernet frames with a VLAN identifier. It inserts a 4-byte tag into the frame after the source MAC address and before the EtherType, signaling which VLAN the frame belongs to. The tag uses a Tag Protocol Identifier of 0x8100 to indicate a VLAN tag, and the Tag Control Information includes a 12-bit VLAN ID (allowing up to 4096 VLANs) plus 3 bits of priority and a 1-bit Canonical Format Indicator. This tagging lets multiple VLANs share the same physical link by keeping traffic separated as it traverses switches. The other options don’t fit because they refer to tagging concepts at different layers or in vague terms: IP tagging is a network-layer idea, while frame tagging or port tagging aren’t the standard terms used for the VLAN tagging mechanism defined by 802.1Q.