Allied Telesis AT-S63 - Manual (Page 609)

AT-S63 Management Software Menus Interface User’s Guide
Section VI: VLANs 609
ˆ Tagged and Untagged Ports
ˆ Port VLAN Identifier
Note
For explanations of VLAN name and VLAN identifier, refer back to
“VLAN Name” on page 602 and “VLAN Identifier” on page 602.
Tagged and
Untagged Ports
You need to specify which ports will be 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.
Port VLAN
Identifier
As explained earlier in the discussion on port-based VLANs, the AT-S63
management software automatically assigns a PVID to each port when a
port is made a member of a VLAN. The PVID is always identical to the
VLAN’s VID, and that in a port-based VLAN packets are forwarded based
on the PVID.
Because a tagged port determines VLAN membership by examining the
tagged header within the frames that it receives, you could 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.
Guidelines to
Creating a
Tagged VLAN
Below are the guidelines to 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 switch can support up to a total of 4094 port-based, tagged,
protected ports, and MAC address-based VLANs. (MAC address-
based VLANs are supported only on the AT-9424Ti/SP switch.)