What is Q-Tagging?

• A. Time synchronization across switches.
• B. Separation of data and control planes.
• C. Route summarization in OSPF.
• D. VLAN tagging on trunk links, defined by the 802.1Q standard.

Answer: (D)

VLAN tagging on trunk links, defined by the 802.1Q standard, is what Q-Tagging refers to. It involves inserting a small tag into Ethernet frames so a single physical link can carry traffic for multiple VLANs. This tag identifies the VLAN the frame belongs to (and can carry priority information), allowing switches to forward the frame to the correct VLAN while keeping traffic separated from other VLANs. On access ports, frames typically leave untagged, while on trunk ports they travel with the 802.1Q tag. This tagging is what enables VLANs to span across multiple switches and maintain isolation between different network segments.