Allied Telesis AT-S24 - Manual (Page 102)

Configuring Virtual LANs and Quality of Service
102
Overview
As the size and traffic on Ethernet networks have grown, new methods
have been needed for segmenting the network to improve network
performance and speed. One of the principal methods for improving
network performance is through the use of VLANs. The VLAN feature
allows you to segment your network through software management by
creating subnetworks. The use of VLANs allow you to group the
workstations, servers, and other networking equipment connected to
your switches into logical workgroups. These VLAN groupings can be
based on similar data needs or security requirements.
When networking devices, such as workstations and servers, are
grouped into a VLAN, data is exchanged between only those members
of the group. In more basic terms, just as switches separate collision
domains, VLANs separate broadcast domains.
Each VLAN constitutes one broadcast domain; therefore, frames are not
permitted to cross a VLAN boundary. This allows for several VLAN-based
broadcast domains to exist on the same switch.
Other advantages of VLANs include:
" You can group workstations logically or functionally, regardless of
their physical location on the network.
" You can change VLAN memberships anytime by software
configuration without moving the workstations physically, or
change group memberships by simply moving a cable from one
port to another.
" With VLAN tagging, the ability to group workstations into logical
work groups is more versatile. Network servers or other network
resources can be shared without loss of data isolation or security.
" With VLAN tagging, one port on a switch can be configured to be
an uplink to another 802.1Q-compatible switch. This one port can
be configured to carry traffic from all VLANs configured on the
switch. (With port-based VLANs, one uplink port is required for
each VLAN in order to uplink VLANs in other switches.)
The Fast Ethernet switches are capable of supporting two types of
VLANs:
" Port-based VLANs
" Tagged VLANs
These different types of VLANs are described in the following sections.