VLAN Terms
VLAN Operation and Network Applications 12-5
Filtering Database
Identifier (FDB ID) Addressing information that the device learns about a VLAN is
stored in the filtering database assigned to that VLAN. Several
VLANs can be assigned to the same FDB ID to allow those
VLANs to share addressing information. This enables the devices
in the different VLANs to communicate with each other when the
individual ports have been configured to allow communication to
occur.
The configuration is accomplished using the Local Management
VLAN Forwarding Configuration screen. By default a VLAN is
assigned to the FDB ID 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.
Table 12-1 VLAN Terms and Definitions (Continued)
VLAN Term Definition