VLAN tagging, typically using the IEEE 802.1Q standard, inserts a tag into the Ethernet frame header. This tag contains a VLAN ID, which allows a switch to identify the VLAN to which the frame belongs. The primary advantage of this on a trunk port is that a single physical link can carry traffic for multiple VLANs simultaneously, with each frame's tag identifying its specific VLAN. This tagging mechanism also ensures that traffic from different VLANs remains logically separate and isolated from each other while traversing the shared trunk link.

A. VLAN tagging is specifically for tagged traffic. Untagged traffic is handled by the native VLAN and is not transferred across different VLANs by the tagging mechanism.

B. Tagging adds a 4-byte header to each frame, which introduces a small amount of overhead. It does not increase the physical link's bandwidth.

1. Juniper Networks Documentation. (2023). Understanding VLANs. Junos OS for EX Series Switches. "To allow traffic from multiple VLANs to traverse a single link

you must use trunk ports. Trunk ports can carry traffic for multiple VLANs... To distinguish which traffic belongs to which VLAN

the switch uses VLAN tags."

2. Juniper Networks Documentation. (2023). Trunk Ports. Junos OS. "Trunk ports multiplex traffic from several VLANs over a single physical connection... To distinguish which traffic belongs to which VLAN

the switch uses VLAN tags." This implies both carrying multiple VLANs (D) and keeping them distinct (C).