Vlan tagging – HP 445946-001 User Manual
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VLANs
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VLAN tagging
The switch supports IEEE 802.1Q VLAN tagging, providing standards-based VLAN support for Ethernet
systems.
Tagging places the VLAN identifier in the frame header, allowing each port to belong to multiple VLANs.
When you configure multiple VLANs on a port, you must also enable tagging on that port.
Since tagging fundamentally changes the format of frames transmitted on a tagged port, you must
carefully 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.
•
Tagged frame—a frame that carries VLAN tagging information in the header. The 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 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 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 (original VID remains).
NOTE:
If an 802.1Q tagged frame is sent to a port that has VLAN-tagging disabled, then the
frames are forwarded based on their port-VLAN ID (PVID).