D-Link DES-3326 User Manual page 70

DES-3326 Layer 3 Fast Ethernet Switch User's Guide
carries the IEEE 802.1Q/802.1p tag. The tag is contained in the
following two octets and consists of 3 bits or user priority, 1 bit of
Canonical Format Identifier (CFI – used for encapsulating Token
Ring packets so they can be carried across Ethernet backbones)
and 12 bits of VLAN ID (VID). The 3 bits of user priority are used
by 802.1p. The VID is the VLAN identifier and is used by the
802.1Q standard. Because the VID is 12 bits long, 4094 unique
VLANs can be identified.
The tag is inserted into the packet header making the entire
packet longer by 4 octets. All of the information contained in the
packet originally is retained.
Figure 5-8. IEEE 802.1Q Tag
The EtherType and VLAN ID are inserted after the MAC source
address, but before the originial EtherType/Length or Logical Link
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Switch Management and Operating Concepts