Allied Telesis AT-S25 - Manual (Page 121)

AT-S25 Management Software User’s Guide
121
You could assign this number manually or allow the management
software to do it automatically. If you allow the management software to
do it automatically, it will simply select the next available VID. This is
acceptable when you are creating a new, unique VLAN.
If you are creating a VLAN on a switch that will be part of a larger VLAN
that spans several switches, then you will need to assign the number
yourself so that the VLAN has the same VID on all switches.
Untagged Ports Naturally, you need to specify which ports on the switch are to be
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 names derive from the fact that the frames received on a
port will not contain any information that indicates VLAN membership,
and that VLAN membership will be determined solely by the port’s PVID.
(There is another type of VLAN where VLAN membership is determined
by information within the frames themselves, rather than by a port’s
PVID. This type of VLAN is explained in Tagged VLAN Overview on page
125.)
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 also needs to be assigned the value 5.
Some switches and switch management programs require that you
assign the PVID value for each port manually. However, the AT-S25
management software performs this task automatically. The software
automatically assigns a PVID to a port, making it identical to the VID of
the VLAN to which the port is an untagged member.
General Rules
to Creating a
Port-based
VLAN
Below is a summary of the general rules to observe when creating a port-
based VLAN.
❑ Each port-based VLAN must be assigned a unique VID. If a
particular VLAN spans multiples switches in a stack, each port of
the VLAN on the different switches must be assigned the same
VID.