Allied Telesis AT-S79 manual Port Vlan Identifier Guidelines to Creating a Tagged Vlan

Tagged and Untagged Ports

Port VLAN

Identifier

Guidelines to Creating a Tagged VLAN

AT-S79 Management Software User’s Guide

Note

For explanations of VLAN name and VLAN identifier, refer back to “VLAN Name” on page 74 and “VLAN Identifier” on page 74.

You need to specify which ports will be members of the VLAN. In the case of a tagged VLAN, the ports usually consist of both untagged and tagged ports. You specify which ports are tagged and which untagged when you create the VLAN.

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.

As explained earlier in the discussion on port-based VLANs, the PVID of a port determines the VLAN where the port is an untagged member.

Because a tagged port determines VLAN membership by examining the tagged header within the frames that it receives, you could conclude that there is no need for a PVID. However, the PVID is used if a tagged port receives an untagged frame — a frame without any tagged information. The port forwards the frame based on the port’s PVID. This is only in cases where an untagged frame arrives on a tagged port. Otherwise, the PVID of a tagged port is ignored.

Below are the guidelines to creating a tagged VLAN.

ˆEach tagged VLAN must be assigned a unique VID. If a particular VLAN spans multiple switches, each part of the VLAN on the different switches must be assigned the same VID.

ˆA tagged port can be a member of multiple VLANs.

ˆAn untagged port can be an untagged member of only one VLAN at a time.

ˆThe switch can support up to a total of 256 port-based and tagged VLANs.

Section I: Using the Menus Interface 81