Allied Telesis AT-S62 - Manual (Page 556)

Chapter 24: Port-based and Tagged Virtual LANs
556 Section V: VLANs
Note
For an explanation of VLAN name and VLAN identifier, refer back to
VLAN Name and “VLAN Identifier” on page 548.
Tagged and Untagged Ports
You need to specify which ports will be members of the VLAN. In the case
of a tagged VLAN, this will usually be 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.
Port VLAN Identifier
As explained earlier in the discussion on port-based VLANs, the
management software automatically adjusts the PVID of a port when a
port is made an untagged member of a VLAN. It is adjusted to match the
VLAN’s VID.
Because a tagged port determines VLAN membership by examining the
tagged header within the frames that it receives, you might conclude that
there is no need for a PVID. However, the PVID is used if a tagged port
receives an untagged frame—a frame without any tagged information.
The port forwards the frame based on the port’s PVID. This is only in
cases where an untagged frame arrives on a tagged port. Otherwise, the
PVID of a port is ignored on a tagged port.
General Rules for
Creating a
Tagged VLAN
Below is a summary of the rules to observe when creating a tagged VLAN.
ˆ Each tagged VLAN must be assigned a unique VID. If a particular
VLAN spans multiple switches, each part of the VLAN on the different
switches must be assigned the same VID.
ˆ A tagged port can be a member of multiple VLANs.
ˆ An untagged port can be an untagged member of only one VLAN at a
time.
ˆ The AT-8500 Series switch can support up to 255 tagged VLANS.