Allied Telesis AT-S39 - Manual (Page 129)

AT-S39 User’s Guide
129
Tagged and Untagged Ports
You must specify which ports are members of the VLAN. In the case of a
tagged VLAN, VLAN members are usually a combination of both tagged
and untagged ports. When you create the VLAN, you specify which ports
are tagged and which ports are untagged.
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.
Because a tagged port determines VLAN membership by examining the
tagged header within the frames that it receives and not by the PVID, it
may seem that PVIDs are unnecessary on a tagged port.
While a tagged port’s PVID is usually ignored, a tagged port can receive
an untagged frame (that is, a frame without any tagged information). In
this scenario, the port forwards the untagged frame by using the port’s
PVID.
General Rules to Creating a Tagged VLAN
Below is a summary of the rules to observe when creating a tagged
VLAN.
❑ Assign each tagged VLAN a unique VID. If a particular VLAN spans
multiple switches or stacks, each part of that VLAN on the
different switches or stacks 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-8000 Series switch can support up to 32 tagged and port-
based VLANS.