IEEE 802.1Q Vlan Tagging

Vlan Tagging is a networking standard written by IEEE 802.1 workgroup allowing muliple bridged networks transparently share same physical network lilnk without leadgae of information between networks. IEEE 802.1Q ---- along with its shortened from dot1q ---- is commonly used refer to the encapsulation protocol used to implement this mechanism over Ethernet networks.

respect to the specific conceptual model underpinning bridging at the MAC layer and to the IEEE 802.1D spanning tree protocol. This protocol allows for individual VLANs to communicate with on another with the use of a switch with layer-3 capabilities, or a router.

reference

Frame format

TPID: Tag protocol identifier
PCP: Priority Code Point
CFI: Cononical Format Indicator
VID: vlan identifier
VTP: VLAN trunking Protocol: a Cisco proprietary VLAN management protocol


Double-tagging
Triple-tagging

defines the encapsulation protocol used to multiplex VLANS over a single lilnk, by adding VLAN tags. However, it is possible to send frames either tagged or untagged, so to help explain which frmes will be sent with or without tags


Trunk Ports: is that once a port is designated as a Trunk port, it will forward and receive tagged frames.
Native vlan: Frames belonging to the Native Vlan do not carry vlan tags when sent over the trunk. Conversely, if an untagged frame is received on a trunk port, the frame is associated with the native valan for this port.