Allied Telesis AT-9000 Series - Manual (Page 126)

Chapter 11: Setting Port-based and Tagged VLANs
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Overview
A VLAN is a group of ports that form a logical Ethernet segment on an
Ethernet switch. The ports of a VLAN form an independent traffic domain
in which the traffic generated by the nodes remains within the VLAN.
VLANs let you segment your network through the switch’s management
software so that you can group nodes with related functions into their own
separate, logical LAN segments. These VLAN groupings can be based on
similar data needs or security requirements. For example, you could
create separate VLANs for the different departments in your company,
such as one for Sales and another for Accounting. Both port-based and
tagged VLANs are supported in the web interface.
Port-based
VLANs
A port-based VLAN is a group of ports on a Gigabit Ethernet Switch that
form a logical Ethernet segment. Each port of a port-based VLAN can
belong to only one VLAN at a time. A port-based VLAN can have as many
or as few ports as needed. The VLAN can consist of all the ports on an
Ethernet switch, or just a few ports. In addition, a port-based VLAN can
span switches and consist of ports from multiple Ethernet switches.
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 do not contain any information
that indicates VLAN membership, and that VLAN membership is
determined solely by a port’s PVID.
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 a port on which a frame is received, and forwards a frame only
to those ports with the same PVID. Consequently, all ports of a port-based
VLAN must have the same PVID. In addition, the PVID of the ports in
a VLAN must match the VLAN’s VID.
For example, if you create a port-based VLAN on the switch and assign it
the VID 5, the PVID for each port in the VLAN must be assigned the value
of 5.
Tagged VLANs The second type of VLAN is the tagged VLAN. VLAN membership in a
tagged VLAN is determined by information within the frames that are
received on a port. This differs from a port-based VLAN, where the PVIDs
assigned to the ports determine VLAN membership.