Ebook Lan

Virtual Local Area Networks - VLANs
They aren’t dead—and they may be the most important part of your next network!

Table of Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 What is a Virtual LAN? – Quick Review . . . . . . . . . . . . . . . . . . . . 2 What facilitated the need for VLANs . . . . . . . . . . . . . . . . . . . . . . 3Hubs and Routers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Switches and VLANs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 VLAN Assignment Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Why Use VLANs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Security and Mobility . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . 6 Administrative Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Quality of Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 VLAN Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 802.1Q and 802.1p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 VLANImplementations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 VLAN Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Product specifications contained in this document are subject to change without notice. Contact your local Alcatel representative for the most current information. Copyright © 2001 Alcatel Internetworking, Inc. All rights reserved. Thisdocument may not be reproduced in whole or in part without the express written permission of Alcatel Internetworking, Inc. Alcatel® and the Alcatel logo are registered trademarks of Alcatel. All other trademarks are the property of their respective owners. Part #030770-00

Virtual Local Area Network - VLAN

3

What facilitated the need for VLANs

Early Router-Centric Network

Hubs andRouters
The primary weakness of the hub and router model is congestion localized in the shared media hub. Multiple devices sharing the same bandwidth creates congestion, which propagates delay. Routers are utilized in this design to force segmentation of the shared bandwidth - however, this segmentation is based on physical connections rather than the dynamic needs of the business environment. Byemploying centralized routing services to implement this segmentation, latency is introduced to the network. Latency and delay do not support the applications and the business goals of the enterprise.

This can be reduced or eliminated by redeploying the routing services to the edge of the network and using switches to provide backbone connectivty. Employing switches provides the user with fastaccess to the servers and other network resources, as well as facilitating the ability to create a flatter network architecture. This is similar to an ATM network's need for ELANs (Emulated Local Area Network).

April, 2001

by Perry Correll

Virtual Local Area Network - VLAN

4

Switched / VLAN Network

Switches and VLANs
Switches and VLANs allow the network manager to segment thenetwork with a logical, hierarchical structure. With this overlay, logical associations can be made between servers and users by using policies, regardless of device location. These logical structures are called broadcast domains because they confine the broadcast traffic. • • The Port Policy gives the network manager the ability to assign network connectivity to specific sets of ports within theswitch. This is ideal for use in cases where ports are being used for backbone connectivity. The MAC Address Policy provides a high degree of mobility and security. If the MAC address matches a VLAN policy, the device gains access to the assigned services. If no match is made, no connectivity or services are provided.

VLAN Assignment Methods
Policy-based VLANs provide various methods for...