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IEEE 802.1Q, often referred to as Dot1q, is the networking standard that supports virtual local area networking (VLANs) on an IEEE 802.3 Ethernet network. The standard defines a system of VLAN tagging for Ethernet frames and the accompanying procedures to be used by bridges and switches in handling such frames.
Insertion of the 802.1Q VLAN tag (four octets) into an Ethernet-II frame, with a typical VLAN arrangement of a tag protocol identifier (TPID) EtherType value of 0x8100. A QinQ arrangement would add another four-octet tag containing a two-octet TPID using various EtherType values.
The IEEE 802.1Q tag or IEEE 802.1ad tag, if present, is a four-octet field that indicates virtual LAN (VLAN) membership and IEEE 802.1p priority. The first two octets of the tag are called the T ag P rotocol ID entifier (TPID) and double as the EtherType field indicating that the frame is either 802.1Q or 802.1ad tagged. 802.1Q uses a TPID of ...
IEEE 802.3 is a working group and a collection of standards defining the physical layer and data link layer's media access control (MAC) of wired Ethernet. The standards are produced by the working group of the Institute of Electrical and Electronics Engineers (IEEE).
IEEE 802 is a family of Institute of Electrical and Electronics Engineers (IEEE) standards for local area networks (LANs), personal area networks (PANs), and metropolitan area networks (MANs). The IEEE 802 LAN/MAN Standards Committee (LMSC) maintains these standards.
IEEE 802.1ad is an amendment to the IEEE 802.1Q-1998 networking standard which adds support for provider bridges. It was incorporated into the base 802.1Q standard in 2011. [ 1 ] The technique specified by the standard is known informally as stacked VLANs or QinQ .
Under IEEE 802.1Q, the maximum number of VLANs on a given Ethernet network is 4,094 (4,096 values provided by the 12-bit VID field minus reserved values at each end of the range, 0 and 4,095). This does not impose the same limit on the number of IP subnets in such a network since a single VLAN can contain multiple IP subnets.
With ISL, an Ethernet frame is encapsulated with a header that transports VLAN IDs between switches and routers. With IEEE 802.1Q the tag is internal. This is a key advantage for IEEE 802.1Q as it means tagged frames can be sent over standard Ethernet links. ISL does add overhead to the frame as a 26-byte header containing a 10-bit VLAN ID.