Allied Telesis AT-S41 - Manual (Page 92)

AT-S41 User’s Guide
92
In a VLAN that consists of only untagged ports, port membership is
determined by what is referred to as the port VLAN identifier (PVID). This
is a number that you must assign to a port to make it an untagged
member of a VLAN. The PVID of a port will be the same as the VID of the
VLAN in which the port is to be an untagged member. You can assign
each port only one PVID. Consequently, a port can be an untagged
member of only one VLAN at a time.
Here is an example. Let’s assume that you are creating a new VLAN
called Sales and that you assigned the VLAN a VID of 4. You have
decided that Ports 1 through 4 on a switch will be untagged members of
the new VLAN. Consequently, you would assign Ports 1 to 4 PVIDs of 4,
the same as the VID. Now, when the switch receives a frame on one of
the ports on the Sales VLAN and it needs to broadcast the frame to the
other ports of the VLAN, it will know that the VLAN consists of Ports 1 to
4.
Note
The AT-8350GB stack is pre-configured with one port-based VLAN,
called the Default VLAN. All ports on the stack are members of this
VLAN. The Default VLAN has a VID of 1. Consequently, all the ports in
the VLAN have a PVID value of 1.
The ports are called untagged because the switch assumes that the
frames received on this type of port will not contain any information that
indicates VLAN membership and that VLAN membership will be
determined solely by a port’s PVID. (This contrasts with tagged ports,
explained next, where VLAN membership is determined by information
within the frames themselves.) Frames received on untagged ports and
lacking any VLAN identifying information are referred to as untagged
frames.
When a switch receives a frame on an untagged port, it first examines
the PVID of the port on which the frame was received and then adds the
PVID to the frame itself. It then examines the destination MAC address of
the frame. If the destination address is in the MAC address table and if
the switch port where the destination node is located is part of the same
VLAN as the port that received the frame, the switch sends the frame out
the port to the destination node.
If the destination MAC address is not in the MAC address table, the
switch broadcasts the frame to all the ports that share the same PVID as
the port that received the frame.