Allied Telesis AT-9000/52 User Manual

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AlliedWare Plus Version 2.1.2 Management Software Web Browser User’s Guide
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The VLAN information within an Ethernet frame is referred to as a tag or 
tagged header. A tag, which follows the source and destination addresses 
in a frame, contains the VID of the VLAN to which the frame belongs (IEEE 
802.3ac standard). This number uniquely identifies each VLAN in a 
network.
When the switch receives a frame with a VLAN tag, referred to as a tagged 
frame
, the switch forwards the frame only to those ports that share the 
same VID.
A port that receives or transmits tagged frames is referred to as a tagged 
port
. Any network device connected to a tagged port must be IEEE 
802.1Q-compliant. This is the standard that outlines the requirements and 
standards for tagging. The device must be able to process the tagged 
information on received frames and add tagged information to transmitted 
frames. 
Tagged and
Untagged Ports
You need to specify which ports are members of the VLAN. In the case of 
a tagged VLAN, it is usually a combination of both untagged ports and 
tagged ports. You specify which ports are tagged and which untagged 
when you create the VLAN.
An untagged port, whether a member of a port-based VLAN or a tagged 
VLAN, can be in only one VLAN at a time. However, a tagged port can be 
a member of more than one VLAN. A port can also be an untagged 
member of one VLAN and a tagged member of different VLANs 
simultaneously.