Wireless bridging, i.e. connecting two wired networks via a wireless link has gotten to be a very confusing subject. In this NTK, we're going to try to untangle the mess that wireless networking companies have made of this product area, help you choose the right products for your application, and show you how to set them up properly.

We've got a lot to do, so let's get started.

Not too long ago, if you wanted to connect two wired networks together via a wireless link, you looked for a product called a wireless bridge. They tended to cost close to $500, and only talked to other bridge devices. Life was simple, but expensive.

In late 2001, consumer networking companies were looking to add features to their 802.11b APs in order to differentiate themselves in a market that was making their products pretty much a commodity. Up until then, Access Points had just one mode, which allowed client devices operating in Infrastructure mode to associate (connect) and access the wired LAN that the Access Point was connected to.

So to spice things up a bit, manufacturers started adding bridging features to their Access Points. The new features added the ability for Access Points to connect to other Access Points to form wireless bridges. Unfortunately, most companies continued to call these products "Access Points", and therefore started down the path to consumer confusion. With prices of these improved Access Points dropping to around $100, life got a little more confusing, but much less expensive!

In late Summer / early Fall 2002, things got even more confusing (but not less expensive!) with the addition of a new class of products, also capable of wireless bridging. These products, such as Linksys' WET11, go by different names, but provide the ability to take any device with an Ethernet connector and connect it to a wireless network. If the manufacturers had stopped there, I probably wouldn't be writing this article, since it would be clear that these products were basically a wireless client adapter that connected to a computing device via an Ethernet port instead of the USB, CardBus, PC Card, or PCI buses that previous adapters sported.

But manufacturers didn't stop and instead gave these devices the ability to support multiple devices (typically up to 20) connected to their single Ethernet connector. But wait, isn't that we could already do with the Access Point / Bridges? What do these new products do that can't already be done?

Let's start by looking at combination AP/Bridges and the various ways they can be used.

NOTES:
1) Although manufacturers have somewhat standardized on the nomenclature they use to describe AP/Bridge modes, you may find that your particular product uses a different term.

2) When using the bridging functions of AP/Bridges, we recommend you use the same product at both ends of the bridge. Although you might luck out and get a wireless bridge working between two different manufacturers' products, you won't get any help if you call a vendor's support line because most companies support bridging between their products only.

3) The connection diagrams use IP addresses to help you keep track of the network segment (subnet) that a device is part of. Your IP addresses may be different!

4) Unless otherwise noted, you should set each bridge device to the same SSID (or ESSID), same channel (if offered as an option), and same WEP mode (and WEP key if WEP is enabled).

Once you select a product, you'll have to configure it. There are a number of wireless bridging modes, and as noted above, manufacturers don't always use the same terminology. But most AP/Bridges offer three modes of operation, which are described in the next sections.

The simplest bridging mode is where two bridge units connect to each other. You usually enter the MAC address of the unit on the opposite end of the wireless bridge in each bridge's configuration screen. Manufacturers are pretty consistent in describing this mode and the way it's set up. Figure 1 illustrates a Point-to-Point bridge.

Note that although only one client is shown on the far side of the bridge, you can have multiple clients, usually somewhere between 20 and 32.

Figure 1: Point-to-Point bridge

Tip: Each AP/Bridge device has its own IP address. Although most products can be set to have the AP/Bridge obtain its IP address via DHCP, we recommend you set the IP information statically. This makes things much easier to troubleshoot when you're having network connectivity problems!

This mode allows multiple wired networks to be connected. The exact modes (and their names) used in the setup vary from manufacturer to manufacturer, but most all AP/Bridges also support this capability. For performance reasons, you should limit your multipoint network to three segments as shown in Figure 2. Again, you can have multiple wired clients in all network segments.

Figure 2: Multi-point bridge

 

Tip: This mode's setup tends to vary a little. SMC's 2682W, for example, requires one unit to be set as a "Bridge Master", and the other bridge units to be set as "Bridge Slaves". Linksys' WAP11 has you set one unit to Point-to-Multipoint, and the others to Point-to-Point mode, with the "Remote MAC address" set to the MAC address of the box set to Point-to-Multipoint mode.

This mode sets the AP/Bridge so that it will work with a normal Access Point, Wireless router, or AP/Bridge set to normal Access Point mode. The unit that is set to AP Client mode will connect to the AP using the normal AP Infrastructure mode, instead of a special bridge mode. Figure 3 shows a setup using this mode, which at first glance may look exactly like Figure 1!

Figure 3: Bridge using AP Client

If you look closely, however, you'll see that in this mode, the top (local) "bridge" device is just a normal Access Point, which also supports wireless clients. The bottom (remote) end uses an AP/Bridge set to AP Client mode, which can't support wireless clients.

Tip: Implementations of "AP Client" mode tend to be vendor specific and not guaranteed to work when you mix equipment from different vendors. If you plan to use "AP Client" mode to build your bridge, I recommend you use two of the same device.

If you've followed us so far, hang on, because things are going to get a little more confusing as we next take a look at the newest class of device.

Wireless Ethernet Bridges