Specifications

Getting Started with HP ProCurve Switching and Routing
Module 2 – 38 Rev. 9.41
IEEE 802.1Q standard
VLANs are based on the IEEE 802.1Q standard.
IEEE 802.1Q perform "explicit tagging": the frame itself is tagged with VLAN
information, which is a 4-byte field that can be inserted into an Ethernet frame. As
shown below, this field includes a VLAN ID, allowing each Ethernet frame to be
identified as part of a particular VLAN.
802.1Q-compliant devices (such as most managed switches) can insert this field into
the Ethernet frame or remove it, as needed.
Devices that do not support 802.1Q cannot insert or recognize the field. (These
devices may consider a frame with the 802.1Q tag an illegal frame and drop it.)
Switches that support 802.1Q inspect the frame for the tag. If the tag is included,
the switch forwards the frame to a port that is a member of the VLAN identified in
the tag. If the frame is untagged, the switch forwards the frame accordingly.
In the graphic displayed above:
 Tag Protocol ID (TPID) identifies the frame as an 802.1Q frame.
 Tag control Information (TCI) contains three components—one of which
identifies the frame's VLAN.
 User Priority is the field that indicates the priority (or quality of service) of the
VLAN traffic.
 Canonical Format Indicator (CFI) indicates if the information in the frame's
MAC address is in canonical format.
 VLAN ID is the field that associates the frame with a specific VLAN.
For HP Internal Use Only