Enterasys 2H25x User Manual page 267

VLAN Terms
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.
1D Trunk
A connection from a switch that passes only untagged traffic. By default, a port designated as a
1D Trunk port has all VLANs on its Port VLAN List and is configured to transmit all frames as
untagged frames.
VLAN Operation and Network Applications 12-5