Which Layer 2 switch function encapsulates packets from different VLANs so they traverse the same port while keeping traffic separated?

VLAN tagging is the correct answer. It's a Layer 2 function that adds a tag (typically an 802.1Q header) to Ethernet frames. This tag identifies the VLAN to which the frame belongs, allowing multiple VLANs to share a single physical link (a trunk port) while maintaining logical separation of traffic. This is crucial for efficient network design and security. VLAN marking is not a standard networking term; it's often used interchangeably with tagging but is less precise. VLAN numbering refers to assigning a unique ID to each VLAN, which is part of VLAN configuration but not the encapsulation mechanism itself. VLAN DSCP (Differentiated Services Code Point) is a Layer 3 QoS mechanism used for prioritizing traffic, not for encapsulating VLANs.