Ask The Wi-Fi Guru, Episode I

By Aaron Weiss

March 04, 2008

In this new monthly column, Aaron Weiss, our resident Wi-Fi Guru, will answer your burning questions about small-scale Wi-Fi deployments. In this episode, he covers bridging robots, hotspot sharing, and DD-WRT repeaters.

There are many writers you can turn to for advice. Want to know how to confront your mother-in-law about that single-slice toaster she gave on your birthday? Write to Dear Abby. Want to know whether you owe fifty bucks to replace your friends' tire after he drove over a nail in your driveway? Write to The Ethicist. But if you want to know what kind of connector you need to plug a booster antenna into your wireless router, or why your wireless router is much slower than the claims on the box, you can ask The Wi-Fi Guru. You should. Please. We would like that. And unlike The Ethicist, we won't make fun of you. To submit your question, simply click on my name above, and put “Wi-Fi Guru” in the subject line.

Q: I'm a graduate student working on autonomous control of multiple robots. The DD-WRT wireless bridge software looks like something that would be useful in our lab. I'm trying to find out whether or not you can use the

software to link more than two routers. For example, we have our primary router on a desktop and four other routers on four independent robots. Would the DD-WRT software allow the four robots to exchange data among each other and the desktop?

A: The Wi-Fi Guru cannot resist questions about robots. Assuming they are programmed to feel emotion, your robots will be happy to learn that a DD-WRT wireless bridge will let them communicate via the network, exchange data, and talk robot gossip.

In our tutorial about using the DD-WRT open source firmware to build a wireless bridge, the networking device physically attached to the bridged router will receive its IP address from the DHCP server on your LAN—in your case, the primary router. In this scenario, if each robot is physically connected to a router running DD-WRT and configured as a wireless bridge, they will share the same LAN as all wireless clients on your network.

There shouldn't be anything else special you would need to do, other than to make sure your robots don't become self-aware and take over the world.

Q: I just setup wireless in my house using a Linksys WRT54G. I'm thinking of sharing the cost of it via hotspot to my neighbor. How can I manage and control this hotspot? Is there any free hotspot management firmware available and how do I use it?

A: As described in our recent tutorial on setting up a hotspot using DD-WRT, you can use your router to setup several different kinds of hotspots, which vary in features and complexity. When it comes to sharing the cost of your service, there are two ways you could go about managing your hotspot: one, use a hotspot service that lets you directly bill your neighbor for their usage or, two, use a service that lets you simply restrict their usage (in hours or bandwidth) to the proportion of service you've agreed to share with them.

Billing your neighbor directly is probably not the best solution. You would need to use a fee-based hotspot service, which undermines the savings of cost-sharing with one neighbor. Two, your neighbor would probably then bill you when you drop by to borrow sugar. It could get ugly.

Using your WRT54G with DD-WRT, you can use its built in support for Chillispot, an open source hotspot solution. But rather than setup your own Chillispot server, which is a little bit complicated for this small-scale scenario, sign up for a free account at Worldspot.net. Worldspot will provide you with the exact settings you need to plug into the Chillispot configuration page on your router. You can then create an access profile for your neighbor, which limits her usage by your choice of criteria. If your broadband service offers 5Mbps download, for example, and you split the cost 50/50 with your neighbor, you can setup an access profile that limits your neighbor to 2.5Mbps. When you drop by for that sugar, you can collect their half of the service cost.

Q: In your tutorial you explain how to configure DD-WRT as a repeater. I want to have it configured as a repeater, but I want the computers to be on the same network (same IP range). I tried to use the repeater bridge mode and to set the DD-WRT router IP in the same IP range (the non-DD-WRT router IP is 192.168.1.1 and the DD-WRT repeater is 192.168.1.150) Is that ok?

A: Normally, the basic repeater mode of DD-WRT will connect to a wireless router as a client, and rebroadcast the signal under a different SSID. The repeated signal will not be bridged to the host router—meaning, the repeating router will NAT clients associated with it, effectively placing them on a separate LAN segment than clients connected to the host router.

In repeater bridge mode, the concept is that clients connected to the repeating router will receive their IP address from the host router—grouping all clients on the same LAN, whether they are connected to the host router directly or through a repeater.

For users of DD-WRT, the problem is that repeater bridge mode did not work in the developer versions where it first appeared (standard repeater mode matured earlier). A scan of the DD-WRT support forums suggest that at least some users are successfully using repeater bridge mode in the latest developer release, V24 RC7. Because this release is not yet considered officially stable, though, it may or may not introduce other problems depending on other features you may be using.

If you have administrator access to the primary wireless router in your network, another option would be to use WDS rather than repeater mode. For your scenario, WDS should effectively accomplish the same result. Plus, it is more mature and can even be used with some routers, which are not running DD-WRT (assuming they support WDS, which is somewhat common).

Next time on "Ask The Wi-Fi Guru"…

Your wireless networking questions answered! We can't answer every question, of course, but we will try our best to tackle any wireless problems and dilemmas that may be of interest to a wider audience--or if they come wrapped in twenty dollar bills.*

*Not really, sadly.

Aaron Weiss is a freelance writer, editor, and Wi-Fi enthusiast based in upstate New York. To submit your questions to the Wi-Fi Guru, simply click on Aaron's byline and put "Wi-Fi Guru" in the subject line.

 

    


Comment and Contribute
(Maximum characters: 1200). You have
characters left.