Allied Telesis AT-S112 manual Tagged Vlan Overview, General Rules for Creating a Port-based Vlan

Chapter 13: Virtual LANs

Each port of a port-based VLAN can belong to as many VLANs as needed. Therefore, traffic can be forwarded to the members of the groups to which the port is assigned. For example, port 1 and port 2 are members of group 1 and ports 1 and 3 are members of group 2. In this case, traffic from port 1 is forwarded to ports 2 and 3, traffic from port 2 is forwarded only to port 1, and traffic from port 3 is forwarded only to port 1.

Tagged VLAN Overview

General Rules for Creating a Port-based VLAN

Here is a summary of general rules to observe when creating a port-based VLAN:

Assign a unique name to each port-based VLAN.

Assign a unique VLAN Index to each port-based VLAN. If a particular port-based VLAN spans multiple switches, each part of the VLAN on the different switches must be assigned the same VLAN ind ex.

Create up to 52 port-based VLANs.

The second type of VLAN supported by the AT-S112 Management software is the tagged VLAN. In this type of VLAN, membership is determined by tag information within the frames that are received on a port and the VLAN configuration of each port.

The VLAN information within an Ethernet frame is referred to as a tag and is contained in a tagged header for the frame. A tag, which follows the source and destination addresses in a frame, contains the VLAN ID of the VLAN to which the frame belongs (IEEE 802.3ac standard). This number uniquely identifies each VLAN in a network.

When a switch receives a frame with a VLAN tag, referred to as a tagged frame, the switch forwards the frame only to those ports whose VLAN ID equals the VLAN tag.

A port that receives or transmits tagged frames is referred to as a tagged port. Any network device connected to a tagged port must be IEEE 802.1Q-compliant. This is the standard that outlines the requirements and standards for VLAN tagging. The device must be able to process the tagged information on received frames and add tagged information to transmitted frames.

A tagged VLAN consists of the following:

“VLAN Index” on page 153

“VLAN Name” on page 153

“Tagged and Untagged Ports” on page 153

“Port VLAN Identifier (PVID)” on page 153

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