The article is discussing the IEEE 802.1Q VLAN (Virtual Local Area Network) tagging only. In the below sections the topic IEEE802.1Q VLAN (Virtual Local Area Network) and the related topics are briefly explained. IEEE 802.1Q VLAN (Virtual Local Area Network) tagging is a protocol used for VLAN tagging.
IEEE 802.1Q is a non-proprietary protocol used other than the Inter-Switch Link (ISL) protocol. IEEE 802.1Q is used for the interoperability of network devices that have different vendors. Comparing to Inter-Switch Link (ISL), ISL (Inter-Switch Link) combines the Ethernet frame using the ISL header and FCS.
In IEEE 802.1Q inside the Ethernet Frame VLAN (Virtual Local Area Network) information is inserted by using the process called internal tagging. The method used in IEEE 802.1Q is named as Internal Tagging.
The tagged and untagged Ethernet frames are supported by the IEEE 802.1Q. A standard unaltered Ethernet Frame is the untagged Ethernet frame. For the native VLAN (Virtual Local Area Network) communications this type of untagged Ethernet Frames is used.
On a trunk port if an untagged Ethernet frame receives a signal it is taken as a part of native VLAN (Virtual Local Area Network) communication and if a native VLAN (Virtual Local Area Network) trunk port or switch exist then frame from the native VLAN (Virtual Local Area Network) port are not tagged. The four-byte VLAN (Virtual Local Area Network) tag is used with a tagged Ethernet frame but in the untagged Ethernet frame, there is no use of any four-byte VLAN (Virtual Local Area Network) tag field.
In the case of tagged Ethernet Frame in between the original Ethernet frame source address field and the type filed a four-bit field is inserted. After the four-byte tag is inserted FCS (Frame Check Sequence) is calculated. The other name of the IEEE 802.1Q protocol is Dot1Q.
The IEEE 802.1Q is used also to define the Generic Attribute Registration Protocol. The concept of double tagging was established by the IEEE 802.1Q protocol.
The protocols introduced by this IEEE 802.1Q with the advanced features in year by year are Multiple VLAN Registration Protocol (MVRP), GARP VLAN Registration Protocol (GVRP), Multiple Spanning Tree Protocol (MSTP) were introduced. The use of Multiple VLAN Registration Protocol (MVRP) is to delete or remove the VLANs from the bridges that are transferred over the link.
After years passed the protocol introduced with the better feature was GARP (GARP VLAN Registration Protocol) Protocol. Later the standard version that was originally established by IEEE 802.1Q was the Multiple Spanning Tree Protocol (MSTP).
The fields used in IEEE 802.1Q are as follows:
TPID (Tag Protocol Identifier) – TPID (Tag Protocol Identifier) a 16 bit protocol default have a value of 0x8100 to specify 802.1Q tag.
Priority – priority is 3 bites filed. Priority is used to put layer 2 QoS (Quality of Services).
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CFI – the expanded form of CFI is (Canonical Format Identifier) is a 1-bit field. Between the Ethernet and the Token ring CFI (Canonical Format Identifier) is used for the comparison purpose.