Allied Telesis AT-GS950/24 - Manual (Page 160)

Chapter 13: Virtual LANs
160
VLAN Index
You must assign a unique number to each VLAN in a network. This
number is called the Port-Based VLAN Index. This number uniquely
identifies a VLAN in the AT-GS950/24 switch and across the network.
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.
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 index.
 Create up to 52 port-based VLANs.
Tagged VLAN
Overview
The second type of VLAN supported by the AT-S115 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.