Which field identifies the VLAN that a frame belongs to in the 802.1Q tagging?

In 802.1Q tagging, the field that identifies the VLAN to which a frame belongs is the VLAN Identifier (VID). This field is crucial because it allows switches to recognize which VLAN a particular packet should be associated with, enabling the correct processing and routing of traffic across VLANs in a network.

The VID is a 12-bit field that can represent VLANs from 0 to 4095, where VLANs with IDs from 1 to 4095 are considered valid, while 0 is reserved and typically indicates a priority tagging. This allows for a large number of VLANs to be created and managed within a single network infrastructure.

Understanding the role of the VID is essential for network segmentation and maintaining multicast and broadcast traffic within defined boundaries, which is a key aspect of efficient network design and operation. This helps prevent broadcast storms and ensures that network resources are utilized effectively. In contrast, other fields in the VLAN tagging structure serve different purposes, such as managing priority and type of service, but do not directly indicate VLAN membership like the VID does.