Ask the Wi-Fi Guru, Episode VIII

By Aaron Weiss

October 10, 2008

In the October installment of our monthly Q&A column, the Wi-Fi Guru tackles Bluetooth blocking (although he's not sure why), WLANs for WISP subscribers, iPhone tricks, and of course, DD-WRT on a WRT54G.

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In the October 2008 installment of our monthly Q&A column, the Wi-Fi Guru tackles Bluetooth blocking (although he's not sure why), WLANs for WISP subscribers, iPhone tricks, and of course, DD-WRT on a WRT54G.

Most people are generally good and law-abiding citizens who try to do the right thing. We stop at red lights, return money that we've found, and recycle empty bottles. But let's be honest—sometimes we drive over the speed limit. We jaywalk. We "forget" to say anything when the grocery store undercharges us for Portobello mushrooms (hypothetically speaking, of course). And if you use Wi-Fi networks, you may have—once or twice—"borrowed" an unsecured wireless signal from an unsuspecting neighbor or stranger.

A few readers have sent in questions related to this kind of "borrowing." We haven't included any specific examples here, but they all pretty much ask the same thing: is it safe and is it wrong? Far be it for the Guru to weigh in on ethical considerations. The New York Times pays their Ethicist good money to do that. The Guru will say, however, that when engaged in wireless promiscuity, it's important to keep in mind the same advice for such behavior in the physical world: be careful. When you see an unsecured wireless access point and think "woot! free Internet!" you might be giving more than you get. Computers infected with certain malware will sometimes pretend to be free wireless, and when you connect through them, they secretly log any information you send over the network. Associating with strangers carries risks you may regret for days or months afterwards.

For more on hotspot safety, read "How to: Surf Safely with your Mobile Device," '"Free Wi-Fi' May Not Be What It Seems," and "Hotspot Safety for Business Users." 

Q: When using the iPhone internationally, is there a way to be sure you're on Wi-Fi and not using the phone network? I know that icon is at the top for the Wi-Fi, but can you turn off the phone so you're sure you're not popping minutes and MB off at a huge cost?--Tom


A: Even the most devout iPhone lovers would be less than thrilled to receive a $4,800 bill for international data roaming. The iPhone uses both the cellular EDGE network and local Wi-Fi for network access. Although connecting to a wireless AP may be free, using EDGE will incur data charges if you are roaming internationally—big charges. Even though the iPhone will prefer Wi-Fi over EDGE when available, it still must rely on EDGE for features like updating visual voicemail.


Unfortunately, Apple did not build a simple hardware or software switch into the iPhone so that you can manually disable EDGE. From what the Guru hears, it is possible to arrange for your cellular contract to disable international roaming, although this could be inconvenient if you would like spontaneous control over using data roaming. Fortunately, there are two other solutions:


1. Brute force—pull the SIM card. If you remove the SIM from your iPhone, it will not be able to get onto the cellular network. Reports suggest that you can continue to use the iPhone as a network client via Wi-Fi. Of course, this means you also won't be able to make calls using your iPhone until you reinsert the SIM card, making it not so much of a phone and more just an “i.”


2. Users of an iPhone running 1.x firmware can install the Services app, which gives you a nifty little GUI through which you can toggle EDGE, Bluetooth, and Wi-Fi. iPhone 2.x users will need a different app, called BossPrefs, to do the same thing.

For more iPhone tips, read "How to: Surf Safely with your Mobile Device," "Tutorial: iPhone Ringtones Revisited," and "Things to Consider When Using the iPhone Outside the U.S. (Part II)." 


Q: Are you aware of any products that can jam Bluetooth transmission, without introducing any channel pollution to the Wi-Fi network found in range? Can such products interfere (disrupt) one or more of the Bluetooth protocols thus jamming the service? – Ziyad


 A: Was someone looking for the Ethicist earlier? Anyone, anyone? "Ours is not to ask why," as they say—ours is to answer. And the answer is—not really, no.


Bluetooth and 802.1X ("Wi-Fi") both operate in the 2.4Ghz frequency range. Bluetooth uses much lower power than Wi-Fi, and is intended for very local associations of under 30 feet. Wi-Fi, of course, can reach dozens, hundreds, and even thousands of feet with appropriate equipment. You can readily find plans to build a jammer for Bluetooth and Wi-Fi. But a jammer that can single out Bluetooth alone? Seems like a technical impossibility. Perhaps the closest solution would be a low-power directional jammer. With a device like this, you can jam Bluetooth+Wi-Fi coming from one direction while allowing them to continue working from another. So, good luck with that.

To learn more about Bluetooth, Wi-Fi, or other Wi-Fi-related terms, visit our Glossary.


Q: Most of the user manuals and instructions I have found for wireless routers/gateways assume that the Internet connection is via Ethernet/cable modem. I have a wireless ISP and so want to access the Internet through my Linksys WRT54GS. I already have a home wireless net using Airport Extreme. Can you give me a few hints on setup? – Jon


A: One would need more precise information about your WISP ("wireless ISP") to provide detailed instructions, but on its face this seems like a relatively simple configuration to achieve.


When you plug a cable/DSL modem into a wireless router's WAN/Internet port, the router requests an IP address from the ISP's server at the other end of the line. Depending on the protocol in use by that ISP, this request might take place by DHCP or PPPoE, among others, and so your router's Internet connection has to be configured accordingly.


The situation is really no different with a WISP. Depending on the WISP, you probably have some kind of "subscriber unit" (SU) in your premises. This connects to the external antenna you use to receive the WISP signal—or, in the case of some like Clearwire, the antenna might be integrated into the subscriber unit.


Chances are that the SU provided by your WISP connects to your computer using an Ethernet cable. You can probably plug this cable right into your wireless router's WAN/Internet port. If your WISP uses DHCP to assign an IP address, your router will need to be configured likewise (this is usually the default setting). If your WISP uses PPPoE, you should configure the router to use the same, with supplied username and password. There are other possibilities, but you'd have to consult with your WISP for details.


If your SU connects to a PC using USB rather than Ethernet (this shouldn't be very common), then this would not work with your wireless router. In that case, request an Ethernet-based SU from your WISP.


Unless you need two wireless routers for some reason, in the above setup your WRT54GS should server your whole wireless net. The Airport Extreme would seem to be redundant.


You may also want to read: "Review: Apple AirPort Extreme," "How to Choose the Best WRT54G Router for You," and "The Open Source WRT54G Story."


Q: I have purchased a Linksys WRT54G-TM where it was pre-flashed with DD-WRT v24 making it a WRT54-GL. Can I use it to WDS to a WRT54G V8 (factory-No DD-WRT)? Can I keep other users off the WRT54GL DD-WRTv24? – Rick


 A: The stock Linksys firmware in the WRT54G does not officially support WDS. There are reports that more recent versions of Linksys' firmware provide undocumented support for "lazy WDS"—basically, you enter the WRT54G's MAC address in the WDS configuration for your primary router, and hope it works. This does not inspire confidence. Why not install DD-WRT on your WRT54G V8? The flashing procedure requires a few more steps than the V1-4 routers, but it can be done. Then you'd have full WDS support on both routers.


To manage who can associate with which router, a better idea may be to ditch WDS for a wireless repeater bridge using DD-WRT V24 on both routers. This way, each router can run independent settings for a MAC address whitelist and/or security settings. Then, you could use either MAC whitelisting or different WPA passwords to limit clients' access to each router.


See also, "Beyond the WRT54G: DD-WRT for Many Flavors of Hardware," "Wi-Fi Planet Compendium of DD-WRT," and "DD-WRT Tutorial 2: Extend Range with WDS."

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. Click here to read last month's column.



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