Nortel Networks 24T manual Ieee 802.1Q Tagging

Introduction to the BayStack 410-24T Switch

IEEE 802.1Q Tagging

BayStack 410-24T switches operate in accordance with the IEEE 802.1Q tagging rules. Important terms used with the 802.1Q tagging feature are:

•VLAN identifier (VID) -- the 12-bit portion of the VLAN tag in the frame header that identifies an explicit VLAN.

•Port VLAN identifier (PVID) -- a classification mechanism that associates a port with a specific VLAN (see Figures 1-17 to 1-20).

•Tagged frame -- the 32-bit field (VLAN tag) in the frame header that identifies the frame as belonging to a specific VLAN. Untagged frames are marked (tagged) with this classification as they leave the switch through a port that is configured as a tagged port.

•Untagged frame -- a frame that does not carry any VLAN tagging information in the frame header.

•VLAN port members -- a set of ports that form a broadcast domain for a specific VLAN. A port can be a member of one or more VLANs.

•Untagged member -- a port that has been configured as an untagged member of a specific VLAN. When an untagged frame exits the switch through an untagged member port, the frame header remains unchanged. When a tagged frame exits the switch through an untagged member port, the tag is stripped and the tagged frame is changed to an untagged frame.

•Tagged member -- a port that has been configured as a member of a specific VLAN. When an untagged frame exits the switch through a tagged member port, the frame header is modified to include the 32-bit tag associated with the VLAN assigned to that frame. When a tagged frame exits the switch through a tagged member port, the frame header remains unchanged (original VID remains).

•User_priority -- a three-bit field in the header of a tagged frame. The field is interpreted as a binary number, therefore has a value of 0 - 7. This field allows the tagged frame to carry the user-priority across bridged LANs where the individual LAN segments may be unable to signal priority information.

•Port priority -- the priority level assigned to untagged frames received on a port. This value becomes the user_priority for the frame. Tagged packets get their user_priority from the value contained in the 802.1Q frame header.

•Unregistered packet -- a tagged frame which contains a VID where the receiving port is not a member of that VLAN.

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