IEEE 802.1Q
For virtual LANs, the VLANs, there were various proprietary solutions that were combined into one standard in the IEEE 802.1Q standard. This has the advantage that all LAN switches in which 802.1Q is implemented can be integrated into a virtual network and communicate with each other. Comparable tagging data fields are specified in 802.1ad and 801.2ah.
In 802.1Q, VLAN tagging, a marking mechanism for virtual division of data traffic into VLANs, was specified and corresponding data fields for VLAN tagging were inserted into the Ethernet frame. These are four data fields with a total length of 32 bits, of which 2 bytes are used for the Tag Protocol Identifier( TPID) and the other 2 bytes for the Tag Control Information( TCI). The data fields for VLAN tagging are inserted in the Ethernet frame between the data field for the source address and the type field.
The TPID data field is also referred to as Ethertype 802.1Q and is set to the value 0x8100 for VLANs. This value is reserved for VLAN applications. The following data field Priority Code Points( PCP) controls the priority of the Ethernet frame. With these three bits up to eight different service levels between high and low can be defined. The third data field for the Canonical Format Indicator( CFI) shows whether the MAC address is a compliant (canonical) format, and the VLAN Identifier( VID) describes to which VLAN the Ethernet frame belongs.
In addition to VLAN tagging, 802.1Q also specifies Multiple Registration Protocols( MRP) such as the Multiple VLAN Registration Protocol( MVRP), which switches, bridges and other network components use to register attributes of the VLANs and thus support dynamic configuration of the VLANs.