Apple earns enough goodwill with its usually beautiful design and usability that every now and then it gets away with murder. Case in point: the Airport Express.
I recognize that many people are happy with their AE's. I've found that setting up and using just one of them is fairly straightforward and reliable, although the interface design and documentation for the accompanying Airport Utility software are, shockingly for Apple, lousy. (They're about normal for the rest of the industry: confusing, jargon-ridden, incomplete and sometimes, just plain wrong.)
Adding a second AE makes things a little more confusing and lowers the network's reliability. I've gone ahead and added a third, in order to share an Internet connection via a WDS (Wireless Distribution System) network. That, my friends, can make your life miserable.
My home office Airport Express network has spontaneously going psycho enough times now, and I've had enough trouble finding reliable fix-it info, that I thought I'd nail down and publish what works (for me at least) here*.
Some of the following is based on a helpful guide for setting up two AE's posted by "Tesserax" at Apple Discussions.
If you're starting with brand new AE's, fine. Otherwise, if you're trying to fix a problem, resign yourself to blowing the brains out of all the AE's by cold resetting them: For each one, use a paper clip to push down and hold the reset button while plugging the AE in to a power outlet.
For now place all the AE's near each other, plug them in, give them a minute or two to boot up, and then launch Airport Utility (AU). You need to use AU to discover (and write down) the Airport ID (aka the MAC, or Media Access Control, address) of each AE. If they all show up in AU's left hand pane, you can do this by selecting each AE in turn, clicking Manual Setup, and, under the Summary tab, noting the entry for "Airport ID". If all the AE's don't show up, use the Mac's Airport status menu to select the proper network for each one. (Until you link them with one master network, each AE is on its own network.)
Now, start with the AE you're going to use as a base station (Apple calls all of them base stations - confusing). We'll call it MAIN. Make sure it's plugged into power and give it time to boot up.
- Make sure your Mac is connected to MAIN's wireless network by selecting it in your Mac's Airport status menu.
- Launch Airport Utility. MAIN should show up in AU's left hand pane. Select it.
- Click Manual Setup.
- Click the Base Station tab. Enter a name (in this example, "MAIN") and a password. Note that this will be the password for this individual AE, not the network as a whole, which you will set next.
- Click the Wireless tab. Choose "Participate in a WDS network" from the Wireless Mode pop-up menu. Give the network a name. Choose a Radio Mode (I'm using "802.11g only") a Channel (remember it) and a Wireless Security standard (I'm using WPA/WPA2 Personal). Enter a Wireless Password (remember it).
- Click the WDS tab. Choose WDS Main. Select "Allow wireless clients". In the Wireless Remotes area, click the plus sign and enter the Airport ID of the AE that will be closest to MAIN in our network, which you are going to make a Relay (not a Remote). Then click the plus sign and enter the address for your third AE, which will be a Remote. Note that Apple says you can only have one relay between a main base station and a remote.
- Click Update to send all these settings to the MAIN. Give it a minute or two to restart and we hope, show you a steady green LED.
Next we'll set up the second AE, the one that will be closest to MAIN. We'll call this one AE2.
- If the second AE is visible in the left hand pane of AU, select it. Otherwise, use the Mac's Airport status menu to select its network, wait for it to show up in AU, and then select it.
- Choose Manual Setup.
- Click the Base Station tab. Give this AE a name ("AE2" in this example) and password as before.
- Click the Wireless tab. Choose "Participate in a WDS network" from the Wireless Mode pop-up menu. Choose the same channel as you did for MAIN from the Channel pop-up menu and complete the other entries as you did for MAIN.
- Click the WDS tab. Choose "WDS relay" from the pop-up menu. Enter the Airport ID of MAIN in the field for WDS Main. Select "Allow wireless clients". Under WDS Remotes, click the plus sign and enter the Airport ID of the third AE (which you'll be configuring next).
- Click Update to transfer these settings to AE2. Give it a minute or two to restart.
And now the third AE, which we'll call AE3.
- Follow the same procedure as you did for AE2, until you get to the WDS tab.
- Under the WDS tab, choose the WDS Mode of "WDS remote" (not "relay"). Select "Allow wireless clients". In the WDS Main field, enter the Airport ID of AE2 - not of MAIN, as you would quite likely assume (more very un-Apple-like confusion here).
- Click Update to transfer these settings to AE3. Give it a minute or two to restart.
Now, we fervently hope, you have a working WDS network. You'll need to unplug and move AE2 and AE3 to their permanent locations. Feel free to utter a little prayer. If all goes well, when you plug them in again they'll start up and re-create your network as you designed it.
If you find that one or more of the AE's does not discover the others, it could be that it's far enough from its nearest neighbor that it's getting a marginal signal. But you may be able to help it out. If you are working with a laptop Mac or have one available, move it near the marooned AE, use AU to re-enter its settings and restart it: Go to the Base Station menu (not the tab) and select "Restart..." If that doesn't work, you'll probably have to move this AE closer to a neighbor.
If you still have problems, you might try using a different radio channel so as to try to avoid interference. Use AU's Manual Setup to set the MAIN AE to a different channel and then set the others to the same one.
If you still have problems after trying a few different channels, well...
Good luck, good Googling, and let us know what you find.
* I'm no expert, but I gather that wireless networking is inherently a very tricky business, and some of the problems that come up are caused by external factors such as radio interference from broadcasts or other wireless devices. Still, the promise of Apple products is that they solve challenges like this and shield us from the ugly details.
UPDATE, 2009-04-08: I've made the following changes to this post:
1. Thanks to a comment from reader Alan Cifford, I've learned that Apple says you can have only one relay between a main and a remote (see http://support.apple.com/kb/HT2044). So I've deleted the references to adding more than one relay in a chain.
2. For better clarity, in the example network I now call the main base station MAIN, not BASE.