Allied Telesis AT-S25 - Manual (Page 125)

AT-S25 Management Software User’s Guide
125
For explanations of VLAN name and VLAN identifier, refer back to VLAN
Name and VLAN Identifier on page 119.
General Rules
to Creating a
Tagged VLAN
Below is a summary of the rules to observe when creating a tagged
VLAN.
❑ 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.
❑ A tagged port can be a member of multiple VLANs.
❑ An untagged port can be an untagged member of only one VLAN
at a time.
❑ The AT-8316F or AT-8324 Switch can support up to 255 tagged
VLANs.
PARAMETER DESCRIPTION
VLAN Name For explanations of VLAN Name and VLAN Identifier,
refer back to VLAN Name and VLAN Identifier on page
119.
VLAN Identifier
Tagged and
Untagged Ports You need to specify which ports will be members of the
VLAN. In the case of a tagged VLAN, it will usually be a
combination of both untagged ports and tagged ports.
You specify which ports will be 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 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.
Since a tagged port determines VLAN membership by
examining the tagged header within the frames that it
receives, there would seem to be no need for a PVID.
But actually there is. The PVID is used if a tagged port
receives an untagged frame (that is, a frame without
any tagged information). The port will forward the
frame based on the port’s PVID. But this is only in cases
where untagged frames arrive on tagged ports.
Otherwise, the PVID of a port is ignored on a tagged
port.