Vlan Overview - Cabletron Systems SmartSwitch 8-slot User's Reference Manual

Chapter 2: Bridging Configuration Guide
fewer table entries while flow-based bridging provides tighter management and
control over bridged traffic.

VLAN Overview

Virtual LANs (VLANs) are a means of dividing a physical network into several logical
(virtual) LANs. The division can be done on the basis of various criteria, giving rise
to different types of VLANs. For example, the simplest type of VLANs is the port-
based VLAN. Port-based VLANs divide a network into a number of VLANs by
assigning a VLAN to each port of a switching device. Then, any traffic received on a
given port of a switch belongs to the VLAN associated with that port.
The primary use of VLANs is for broadcast containment. A layer-2 (L2) broadcast
frame is normally transmitted all over a bridged network. By dividing the network into
VLANs, the range of a broadcast is limited, i.e., the broadcast frame is transmitted
only to the VLAN to which it belongs. This reduces the broadcast traffic on a network
by an appreciable factor.
The type of VLAN depends upon one criterion: how a received frame is classified as
belonging to a particular VLAN. VLANs can be categorized into the following types:
1. Port based
2. MAC address based
3. Protocol based
4. Subnet based
5. Multicast based
6. Policy based
Detailed information about these types of VLANs is beyond the scope of this manual.
Each type of VLAN is briefly explained in the following subsections.
Port-based VLANs
Ports of L2 devices (switches, bridges) are assigned to VLANs. Any traffic received
by a port is classified as belonging to the VLAN to which the port belongs. For
example, if ports 1, 2, and 3 belong to the VLAN named "Marketing", then a broadcast
frame received by port 1 is transmitted on ports 2 and 3. It is not transmitted on any
other port.
MAC-address-based VLANs
In this type of VLAN, each switch (or a central VLAN information server) keeps track
of all MAC addresses in a network and maps them to VLANs, based on information
2 - 2 SSR User Reference Manual