Configuring a Wireless Distribution System (WDS)

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3COM® CONFIGURING A WIRELESS DISTRIBUTION SYSTEM TECHNICAL BRIEF 2 Wireless Bridge and Wireless Repeater As shown in Figure 1, WDS can be
TECHNICAL BRIEF

Configuring a Wireless Distribution System (WDS) with the 3Com® OfficeConnect® Wireless 11a/b/g Access Point

Overview

This document explains the WDS (Wireless Distribution System) features provided by the 3Com® OfficeConnect® Wireless 11a/b/g Access Point (3CRWE454A72). These features allow you to build a completely wireless infrastructure because the network equipment no

Point-to-Point WDS Link

Point-to-Multipoint WDS Link

longer has to be connected to a wired LAN. Also, WDS features allow you to create large wireless networks by linking several wireless access points with WDS links. WDS is normally used in large, open areas where pulling wires is cost prohibitive, restricted or physically impossible.

3COM® CONFIGURING A WIRELESS DISTRIBUTION SYSTEM TECHNICAL BRIEF

Figure 1: WDS Configurations

Repeater WDS Link

Wireless Bridge and Wireless Repeater

As shown in Figure 1, WDS can be deployed in several configurations. In this document, we will introduce two basic WDS configurations: a wireless bridge and wireless repeater. Wireless Bridge

The wireless distribution system shown in Figure 2 is often called a “wireless bridge” configuration, because it allows you to connect two LANs at the link layer. In Figure 2, the access point (AP) behaves as a standard bridge that forwards traffic between

WDS links (links that connect to other AP/wireless bridges) and an Ethernet port. As a standard bridge, the access point learns MAC addresses of up to 64 wireless and/or 128 total wired and wireless network devices, which are connected to their respective Ethernet ports to limit the amount of data to be forwarded. Only data destined for stations which are known to reside on the peer Ethernet link, multicast data or data with unknown destinations need to be forwarded to the peer AP via the WDS link.

Figure 2: Wireless Bridge Configuration

802.3 Ethernet frame 802.11 four-address format frame WDS link

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3COM® CONFIGURING A WIRELESS DISTRIBUTION SYSTEM TECHNICAL BRIEF

If, for example, an 802.3 Ethernet frame is sent from a wired Station 1 (Sta1) to Sta3 in Figure 2, frame translations are required while the frame forwards through the WDS link between AP1 and AP2. When AP1 receives the 802.3 frame, the frame is translated to a IEEE 802.11 standard four-address format frame before it is sent to a WDS link. In the fouraddress format frame, the MAC address of Sta1, MAC address of AP1, MAC address of AP2 and MAC address of Sta3 are all included in the

Figure 3: Wireless Repeater Configuration

802.11 frame header, and the frame data is same as the original Ethernet frame. Based on information in this four-address format frame, AP2 will reconstruct the 802.3 Ethernet frame when the frame is forwarded to LAN2. If a security algorithm is configured on the APs, AP1(AP2) will encrypt(decrypt) this four-address format frame before frame forwarding. From Sta3’s point of view, the bridging function is transparent; i.e., the received frame is the same as if Sta1 and Sta3 resided on the same LAN.

802.3 Ethernet frame 802.11 three-address format frame 802.11 four-address format frame WDS link

Wireless Repeater

In Figure 3, AP2 is used to extend the range of the wireless infrastructure by forwarding traffic between associated wireless stations and another repeater or AP connected to the wired LAN. Note that the local Ethernet traffic is not forwarded in this mode. Traffic between Sta3 and Sta4 is not forwarded across the WDS link, nor is traffic between Sta5 and Sta6. As with a wireless bridge mode, APs operating in wireless repeater mode need to translate frames into different frame formats when forwarding

frames between wireless connections and WDS links; the 802.11 three-address frame format is used on wireless links connected to wireless stations, while the 802.3 four-address frame format is used on WDS links connected to other access points. Encryption/ decryption algorithms are also invoked if the AP is configured to be secure. The OfficeConnect Wireless 11a/b/g Access Point can function as a wireless repeater or wireless bridge if WDS links are configured between the connected AP pairs appropriately. 3

3COM® CONFIGURING A WIRELESS DISTRIBUTION SYSTEM TECHNICAL BRIEF

Configuring WDS Links on 3Com OfficeConnect Wireless 11a/b/g Access Points

A WDS link is defined as the MAC address pair of the connected APs. To create a WDS link between two OfficeConnect Wireless 11a/b/g Access Points, enter the peer AP’s MAC address on each AP via the Wireless WDS web page. In addition, make sure you configure all WDS APs to work on the same

radio channel. Since WDS links can operate in 2.4GHZ or 5.4 GHZ radio channels, using Auto Channel selection is not appropriate. Below is an example of configuring a WDS.

We will use example AP1 and AP2 with the following MAC addresses (see these MAC addresses in the status page):

AP1 LAN MAC Address:

00-70-46-01-23-45

11a WLAN MAC Address:

00-70-46-01-23-46

11b/g WLAN MAC Address:

00-70-46-01-23-47

AP2 LAN MAC Address:

00-70-46-01-33-62

11a WLAN MAC Address:

00-70-46-01-33-63

11b/g WLAN MAC Address:

00-70-46-01-33-64

To add a WDS link between AP1 and AP2 in 802.11a mode with channel 60 selected:

2. On the WDS page of AP1, enable WDS and enter AP2 WLAN MAC address (00-70-46-01-33-63) with 802.11a mode in a WDS entry as shown in Figure 4.

1. On the wireless page of AP1,enable 802.11a and select channel 60.

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3COM® CONFIGURING A WIRELESS DISTRIBUTION SYSTEM TECHNICAL BRIEF

Figure 4: Configuring WDS Links on AP1

3. On the wireless page of AP2, enable 802.11a standard and select channel 60.

4. On the WDS page of AP2, enable WDS and enter AP1 WLAN MAC address (00-70-46-01-23-46) with 802.11a mode in a WDS entry as shown in Figure 5.

Figure 5: Configuring WDS Links on AP2

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3COM® CONFIGURING A WIRELESS DISTRIBUTION SYSTEM TECHNICAL BRIEF

Pay special attention to avoid the creation of network loops in the network topology while configuring WDS links. If a loop exists in the network, data could be forwarded

and duplicated endlessly between APs. This could crash networks. Several abnormal loops likely created in a WDS configuration are shown in Figure 6.

Security

Spanning Tree Algorithm

Currently, the OfficeConnect Wireless 11a/b/g Access Point can support secured WDS links in WEP mode. In version 1.01, WEP keys must be the same for both radios in the AP, whether WEP or normal access, and all APs in the system need to have the same keys.

As the OfficeConnect Wireless 11a/b/g Access Point doesn’t implement the Spanning Tree algorithm, WDS links should be configured appropriately to prevent loops in the network.

Figure 6: Loops in Wireless Networks with WDS links

Warnings

3Com Corporation, Corporate Headquarters, 350 Campus Drive, Marlborough, MA 01752-3064 To learn more about 3Com solutions, visit www.3com.com. 3Com is publicly traded on NASDAQ under the symbol COMS.

Copyright © 2004 3Com Corporation. All rights reserved. 3Com, the 3Com logo, and OfficeConnect are registered trademarks of 3Com Corporation. Possible made practical is a trademark of 3Com Corporation. All other company and product names may be trademarks of their respective companies. While every effort is made to ensure the information given is accurate, 3Com does not accept liability for any errors or mistakes which may arise. Specifications and other information in this document may be subject to change without notice. Printed in the U.S. on recycled paper 104108-001 05/04