Which identifier helps specify VLAN membership in Ethernet frames?

The Tag Protocol Identifier (TPID) is crucial for specifying VLAN membership within Ethernet frames. This identifier is used in conjunction with the IEEE 802.1Q standard, which is the protocol responsible for VLAN tagging. When a frame is tagged to indicate its VLAN membership, it includes a TPID that is typically set to a specific value, commonly 0x8100. This value informs network devices that the frame is tagged and provides the necessary information for them to recognize the VLAN to which the frame belongs.

In practice, when Ethernet frames are transmitted over a network with VLANs, the TPID allows switches and other networking devices to categorize and manage the traffic appropriately. By reading this identifier, network devices can ensure that frames are delivered to the correct VLAN, maintaining network segmentation and enhancing security.

The other identifiers listed do not serve the same function within VLAN tagging. Consequently, understanding the role of the Tag Protocol Identifier is essential for anyone working with networking concepts, particularly in environments that utilize VLANs for traffic management.