What is the purpose of VLAN tagging and which standard defines 802.1Q?

• A. VLAN tagging carries multiple VLANs over a single trunk; 802.1Q defines the tag on Ethernet frames.
• B. VLAN tagging sets QoS levels; 802.1Q is for wireless networks
• C. 802.1Q defines IP header tagging
• D. VLAN tagging compresses frames

Answer: (A)

VLAN tagging is about carrying traffic for multiple VLANs over a single physical link while keeping each VLAN’s traffic separate. The 802.1Q standard defines the tag that gets inserted into Ethernet frames to identify which VLAN a frame belongs to. This tag, placed between the source MAC address and the EtherType/length field, includes a VLAN identifier so a switch or router knows which VLAN to associate the frame with, and it also carries bits that can help with quality of service if needed. This tagging enables trunk links to carry traffic for many VLANs at once, while access ports continue to carry untagged frames for a single VLAN. The other options miss the core idea: VLAN tagging isn’t simply about QoS in its primary purpose (though it can carry priority bits), it’s not specific to wireless networks, it doesn’t tag IP headers, and it doesn’t involve frame compression.