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VLAN Terms
802.1Q VLAN User’s Guide 1-5
The configuration is accomplished using the Local Management VLAN
Forwarding Configuration screen. By default a VLAN is assigned to the
FID that matches its VLAN ID.
Tag Header (VLAN Tag)
Four bytes of data inserted in a frame that identifies the VLAN/frame
classification. The Tag Header is inserted into the frame directly after the
Source MAC address field. Twelve bits of the Tag Header represent the
VLAN ID. The remaining bits are other control information.
Tagged Frame
A data frame that contains a Tag Header. A VLAN aware device can add
the Tag Header to any frame it transmits.
Untagged Frame
A data frame that does not have a Tag Header.
Default VLAN
The VLAN to which all ports are assigned upon initialization. The
Default VLAN has a VLAN ID of 1 and cannot be deleted or renamed.
Forwarding List
A list of the ports on a particular device that are eligible to transmit
frames for a selected VLAN.
Port VLAN List
A per port list of all eligible VLANs whose frames can be forwarded out
one specific port and the frame format (tagged or untagged) of
transmissions for that port. The Port VLAN List specifies what VLANs
are associated with a single port for frame transmission purposes.
Filtering Database
A database structure within the switch that keeps track of the associations
between MAC addresses, VLANs, and interface (port) numbers. The
Filtering Database is referred to when a switch makes a forwarding
decision on a frame.
1Q Trunk
A connection between 802.1Q switches that passes only traffic with a
VLAN Tag Header inserted in the frame. By default, a port designated as
a 1Q Trunk port has all VLANs in its Port VLAN List and is configured to
transmit all frames as tagged frames. A 1Q Trunk drops all incoming
frames that do not have a VLAN tag.