What protocol is used for Ethernet frame tagging in VLANs?

The protocol used for Ethernet frame tagging in VLANs is IEEE 802.1Q. This standard defines how to add a VLAN tag to Ethernet frames, allowing for the separation of different VLAN traffic within the same physical network infrastructure. The tagging process involves inserting a 4-byte header into the Ethernet frame, which identifies the VLAN to which the frame belongs. This capability is essential for enabling VLANs to coexist on the same network hardware, facilitating better traffic management and improved network security.

The other protocols listed serve different purposes. IEEE 802.3 pertains to the standard for Ethernet networking but does not include VLAN tagging capabilities. IEEE 802.1X is a network access control protocol used for port-based authentication, important for securing access to the network rather than for VLAN tagging. IEEE 802.11 defines the specifications for wireless local area networks (WLANs) and is unrelated to Ethernet frame tagging. Therefore, IEEE 802.1Q is the correct choice for VLAN frame tagging.