Specifications

Chapter 2. IBM System Networking Switch 10Gb Ethernet switch features 53
Because tagging changes the format of frames transmitted on a tagged port, you must plan
network designs to prevent tagged frames from being transmitted to devices that do not
support 802.1Q VLAN tags, or devices where tagging is not enabled.
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. For example, a port with a PVID of 3 (PVID =3) assigns all untagged
frames received on this port to VLAN 3. Any untagged frames received by the switch are
classified with the PVID of the receiving port.
򐂰 Tagged frame: A frame that carries VLAN tagging information in the header. This VLAN
tagging information is a 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.
򐂰 Untagged member: A port that is 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 is configured as a tagged 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 PVID. When a tagged frame exits the
switch through a tagged member port, the frame header remains unchanged (the original
VID remains).
Tagged frame: If a 802.1Q tagged frame is received by a port that has VLAN-tagging
disabled and the port VLAN ID (PVID) is different from the VLAN ID of the packet, then the
frame is dropped at the ingress port.