IEEE 802.1Q is a standard for Virtual LANs (VLANs) and is a part of the IEEE 802.1 group of networking protocols. It allows for the creation of multiple virtual LANs on a single physical network infrastructure, enabling network segmentation and improved traffic management. IEEE 802.1Q, also known as Dot1q.

IEEE 802.1Q Overview:

Purpose:

• Provides a method for adding VLAN identification information to Ethernet frames.
• Facilitates the creation of logical networks within a physical network, allowing better traffic segregation, improved security, and simplified network management.

Key Components:

1. Tagged Frames: Regular Ethernet frames are augmented with additional information known as VLAN tags.
2. VLAN Identifier (VLAN ID): A numeric value assigned to each VLAN, used to differentiate between different VLANs.
3. VLAN Trunking: Allows switches to carry traffic for multiple VLANs over a single physical link.

• Destination Address and Source Address: MAC addresses of the destination and source devices, respectively.
• VLAN Tag: Four bytes added between the source MAC address and the Ethernet payload.
  • Tag Protocol ID (TPID): 16-bit field identifying the frame as an IEEE 802.1Q-tagged frame (usually set to 0x8100).
  • VLAN Identifier (VID): A 12-bit field specifying the VLAN to which the frame belongs. Allows up to 4096 VLANs.
• Ethernet Payload: The actual data being transmitted.

Operation:

1. Frame Tagging: Before transmission, switches tag Ethernet frames with appropriate VLAN IDs.
2. VLAN Membership: Each port on a switch can be configured to belong to one or more VLANs.
3. VLAN Trunking: Switches use trunk links to carry traffic for multiple VLANs between them.
4. VLAN Filtering: Switches filter incoming frames based on their VLAN IDs, forwarding them only to ports assigned to the corresponding VLANs.
5. VLAN Tag Removal: Before forwarding frames to end devices, switches remove the VLAN tags.