CompTIA Network+ (N10-009)Networking ConceptsMedium
A network administrator configures a single trunk link between two switches to carry traffic for multiple VLANs simultaneously. Which standard defines the frame tagging method used to identify VLAN membership on this trunk?
- A802.1Q
- B802.3af
- C802.11ac
- D802.1X
Show answer & explanationAnswer & explanation
Correct answer: A. 802.1Q
IEEE 802.1Q defines VLAN tagging, inserting a 4-byte tag into the Ethernet frame header that identifies which VLAN the frame belongs to, allowing multiple VLANs to share a single trunk link.
Why the other options are wrong
- B. 802.3af defines Power over Ethernet (PoE), unrelated to VLANs.
- C. 802.11ac is a wireless networking standard, not related to VLAN tagging.
- D. 802.1X is a port-based network access control standard for authentication.
802.1Q VLAN Tagging
IEEE 802.1Q is the standard that inserts a VLAN tag into Ethernet frames so a single trunk link can carry traffic for multiple VLANs.
- Adds a 4-byte tag with VLAN ID (0-4094)
- Enables trunking between switches
- Native VLAN traffic is typically untagged
Memory trick: Q marks the tag that keeps VLANs distinct on one wire.