On trunk links carrying multiple VLANs, which tagging protocol is commonly used?

• A. 802.11ac tagging
• B. 802.1Q tagging
• C. STP
• D. DHCPv6

Answer: (B)

On trunk links that carry multiple VLANs, frames must carry a VLAN identifier so switches know which VLAN each frame belongs to as it traverses the link. The standard method for this is 802.1Q tagging. It inserts a small VLAN tag into the Ethernet frame, creating a unique VLAN ID that travels with the frame and lets the receiving switch segregate traffic into the correct VLANs across the shared link. This tagging approach is standardized and widely supported, which is why it’s the correct choice for carrying multiple VLANs on a single physical connection.

The other options don’t fit this use. 802.11ac tagging isn’t a VLAN tagging method for wired trunking, STP is about preventing switching loops rather than tagging frames, and DHCPv6 is about assigning IPv6 addresses rather than labeling frames by VLAN.