BayStack 450 10/100/1000 Series Switches302401-D Rev 00 1-33IEEE 802.1Q TaggingBayStack 450 switches operate in accordance with the IEEE 802.1Q taggingrules. Important terms used with the 802.1Q tagging feature are:• VLAN identifier (VID) -- the 12-bit portion of the VLAN tag in the frameheader that identifies an explicit VLAN.• Port VLAN identifier (PVID) -- a classification mechanism that associates aport with a specific VLAN. For example, a port with a PVID of 3 (PVID =3)assigns all untagged frames received on this port to VLAN 3.• Tagged frame -- the 32-bit field (VLAN tag) in the frame header that identifiesthe frame as belonging to a specific VLAN. Untagged frames are marked(tagged) with this classification as they leave the switch through a port that isconfigured as a tagged port.• Untagged frame -- a frame that does not carry any VLAN tagginginformation in the frame header.• VLAN port members -- a set of ports that form a broadcast domain for aspecific VLAN. A port can be a member of one or more VLANs.• Untagged member -- a port that has been configured as an untagged memberof a specific VLAN. When an untagged frame exits the switch through anuntagged member port, the frame header remains unchanged. When a taggedframe exits the switch through an untagged member port, the tag is strippedand the tagged frame is changed to an untagged frame.• Tagged member -- a port that has been configured as a member of a specificVLAN. When an untagged frame exits the switch through a tagged memberport, the frame header is modified to include the 32-bit tag associated with thePVID. 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 isinterpreted as a binary number, therefore has a value of 0 -7. This field allowsthe tagged frame to carry the user-priority across bridged LANs where theindividual LAN segments may be unable to signal priority information.• Port priority -- the priority level assigned to untagged frames received on aport. This value becomes the user_priority for the frame. Tagged packets gettheir user_priority from the value contained in the 802.1Q frame header.• Unregistered packet -- a tagged frame which contains a VID where thereceiving port is not a member of that VLAN.kombk.book Page 33 Tuesday, June 29, 1999 3:25 PM
