Allied Telesis AT-S39 - Manual (Page 122)

Section II: Local and Telnet Management
122
If a VLAN consists only of ports located on one physical switch in your
network, you would assign it a VID unique from all other VLANs in your
network.
If a VLAN spans multiple switches, the VID for the VLAN on the different
switches should be identical. In this manner, the switches are able to
recognize and forward frames belonging to the same VLAN even though
the VLAN spans multiple switches.
For example, if you had a port-based VLAN titled Marketing that
spanned three AT-8024 switches, you would assign the Marketing VLAN
on each switch the same VID.
You can assign this number manually or allow the management
software to automatically perform this function. If you allow the
management software to automatically assign the VID, the next
available VID will be selected. If you are creating a VLAN on a switch that
is part of a larger VLAN that spans several switches, you must manually
assign the number so that the VLAN has the same VID across all switches
linked in that VLAN.
Untagged Ports
You must specify which ports on the switch are members of a port-
based VLAN. Ports in a port-based VLAN are referred to as untagged ports
and the frames received on the ports as untagged frames. The term
untagged derives from the fact that the frames received on a port will
not contain any information that indicates VLAN membership, and that
such membership will be determined solely by the port’s PVID.
A port on a switch can be an untagged member of only one port-based
VLAN at a time. An untagged port cannot be assigned to two port-based
VLANs simultaneously.
Port VLAN Identifier
Each port in a port-based VLAN must have a port VLAN identifier (PVID).
The switch associates a frame to a port-based VLAN by the PVID
assigned to the port on which the frame is received, and forwards the
frame only to those ports with the same PVID. Consequently, all ports of
a port-based VLAN must have the same PVID. Additionally, the PVID of
the ports in a VLAN must match the VLAN’s VID.
For example, assume that you were creating a port-based VLAN on a
switch and you had assigned the VLAN the VID 5. Consequently, the
PVID for each port in the VLAN would need to be assigned the value 5.