An Enclosure Example | Jeff Duntemanns Drive-By Wi-Fi Guide

A Real Example with Real Hardware

All that being said, I'll now run through a bridging configuration that I've used very successfully. It's shown schematically back in Figure 16.1. The two AP's I use are the D-Link DWL-900AP+. I like the 900AP+ (from the D-Link AirPlus product line) as a bridge for the following reasons:

It's cheap. I got a pair of them for $89 each on sale. This is as cheap as I've ever seen new access points on the retail market and over time they're going to get even cheaper. Texas Instruments, which makes the guts of the AirPlus product line, is fighting for market share.
It's physically small and very light.
It has only one antenna jack, so there's no uncertainty about how to configure the antenna logic for use with a single gain antenna.
The AirPlus product line incorporates the TI 802.11b+ chipset, which provides a modest but significant throughput increase over standard 802.11b.
It can be configured to request an IP address from a DHCP server. By default, the DWL-900AP+ responds to a specific non-routable IP address (currently 192.168.0.50) but it's better to leave all IP assignment to a single DHCP server.
D-Link sells a relatively inexpensive and compatible pair of power over

Ethernet blocks: Injector and tap together should cost no more than $40.

My pair of DWL-900AP+ units went into bridge mode and bridged without a struggle, once I had everything else set up correctly.

What You'll Need

To duplicate my configuration, here's what you'll need:

Two D-Link DWL-900AP+ access points. Make sure both are at the same firmware release level. You can check on D-Link's Web site to see that it's the current level.
One Linksys EZXS55W or some equivalent dedicated switch for the 'far' leg of the network. ('Far' here meaning the leg without the Internet connection.)
One Linksys BEFSR41 router/switch for the 'near' leg of the network..
Two gain antennas capable of bridging the required distance.

If the link will be outdoors, you will also need enclosures and supports for both APs, power over Ethernet (PoE) adapters on both ends, plus all associated cabling. A laptop incorporating a Wi-Fi client adapter with an antenna jack is also extremely useful for aiming the antennas.

Setting It Up

Start by making sure that the 'near' leg of the network works completely, before you even connect the DWL-900AP+.This install assumes dynamic IP addressing through DHCP, so be sure your nearside router has its DHCP server enabled and that all nearside machines are getting their IPs and talking to one another and to the Internet. If there is a Wi-Fi access point attached to the nearside network, take note of what channel it's running on, so you can put the DWL-900AP+ APs on a nonconflicting channel.

I think it makes a lot of sense to perform the initial AP configuration in a lab setup, preferably indoors. Configurations are saved in nonvolatile Flash memory, so when you actually hoist the equipment into its final position, all you will have to do is aim the antennas. The bridging APs will be in the proper mode with all their various parameters intact.

Configuring the Nearside Network

With the nearside network functioning correctly, follow these steps to configure the nearside network for bridging:

Hook up the nearside DWL-900AP+ to a switch port on the nearside router/ switch and apply power.
Bring up a browser from one of the computers on the nearside network and enter the non-routable IP URL to access the AP's internal configuration HTTP server. (For the DWL-900AP+ this is currently http://192.168.0.50.) If you have trouble with this step, check to see that the router is on the same subnet. I changed my Linksys router's base IP address to 192.168.0.1 to eliminate this problem.
Log into the D-Link AP's configuration page and go to the Home tab. Click on the Wireless button. Set the SSID and the channel. It's also handy to give the AP a name, so that when you look it up in the router's DHCP client list later on there's no mistaking which client is the nearside bridging AP. ( Without giving the AP a name, all you'll see is its MAC address, which looks pretty much like everybody else's MAC address…) Leave WEP disabled for now. Click Apply. The AP will reboot itself, and you'll return to the Home|Wireless page.
Click on the Home|LAN button. Select the Dynamic IP Address radio button. This will force the DWL-900AP+ to request an IP from the DHCP server. Once you click Apply, the AP will no longer respond to http://192.168.0.50. A time or two when I did this, the AP got confused and its HTTP server hung. If that happens, power the AP down for ten seconds and power it back up.
Close the browser. Bring up a new browser window and go to your router's configuration page. Find the DHCP clients table listing. For the Linksys BEFSR41, this is reached by clicking the DHCP Clients Table button on the DHCP tab. The DHCP clients table should list all devices that pulled an IP address from the router's DHCP server. Find the entry for the D-Link AP (this is why I earlier suggested giving it a name) and write down the IP address listed for the D-Link AP. This IP address, embedded in an HTTP URL, will be the new address of the AP's configuration page.
Using the D-Link AP's new IP address, log back in to the AP configuration page. Click on the Status tab and write down the AP's Ethernet MAC address. Note that there are two MAC addresses listed: One for Ethernet, and one for wireless. The Ethernet MAC is what you need when you configure the access point on other end of the link.

Configuring the Farside Network

Just as you did with the nearside network, make sure that the farside network is completely functional, and then follow these steps:

Hook up the farside DWL-900AP+ to the farside switch and apply power.
Bring up a browser window and enter the access point's preset configuration page URL, which currently is http://192.168.0.50. Log in. From the Home tab click the Wireless button.
Enter a name for the access point, something different from the name of the nearside AP. This is simply to make it easier to tell the two APs apart in the nearside router's DHCP table. Enter the same SSID you entered for the nearside AP, and the same channel. If there are already one or more Wi-Fi access points on the farside network, make sure the channel is not one already in use by one of those access points. Leave WEP disabled for now. Click Apply.
Click on the Status tab. Write down the Ethernet MAC address for the farside AP. This will have to be entered into the nearside AP's configuration screen to complete the bridge link.
Click on the Advanced tab. Click the radio button for Wireless Bridge. In the Remote Bridge MAC field, enter the Ethernet MAC address of the nearside AP. Click Apply.
Click on the Home tab, and from the Home tab click the LAN button. Click the Dynamic IP Address radio button, and then click Apply. After this step, the farside AP will no longer respond to the preset configuration page address of http://192.168.0.50.

Completing the Bridge Link

At this point, almost everything is configured. What remains is to enter the farside AP's Ethernet MAC address into the nearside AP. Return to the nearside network and follow these steps:

Log into the nearside AP's configuration page using the dynamic IP address it pulled from the DHCP server. This address can always be found by inspecting the DHCP clients table in the router.
Click on the Advanced tab. Click the radio button for Wireless Bridge, and enter the farside AP's Ethernet MAC address into the Remote Bridge MAC field. Click Apply.
Power everything down on both legs of the network and power it up again. If you did everything correctly, the AP and computers on the farside network will use the wireless link to request IP addresses from the nearside router's DHCP server. Your link works!