Ask the Wi-Fi Guru, Episode VI

By Aaron Weiss

August 05, 2008

In the August edition of our monthly Q&A column, the Wi-Fi Guru responds to one of our most popular topics of inquiry: Wi-Fi on boats. He also delves deeper into flashing firmware (for beginners), wireless bridges, DD-WRT, and solves (with a reader's help) Nikki's connection mystery from the last episode.

In the August edition of our monthly Q&A column, the Wi-Fi Guru responds to one of our most popular topics of inquiry: Wi-Fi on boats. He also delves deeper into flashing firmware (for beginners), wireless bridges, DD-WRT, and solves (with a reader's help) Nikki's connection mystery from the last episode.


awhead.pngEach month, we at the Wi-Fi Guru World Headquarters open your mail with glee and anticipation. In the time we've been doing this, an interesting nautical trend has emerged:  Wi-Fi is popular on boats. Can you imagine if the movie Jaws had taken place on a vessel with wireless Internet access? Nobody would have been eaten by the great white shark because they all would have been stuck inside the cabin glued to their laptops. You just know Richard Dreyfuss's character was the kind of guy to constantly update his Facebook status. Roy Scheider would be obsessively cleaning his spam folder. And that scary Jaws music? Downloaded illegally with bittorrent.

Q: Could you please help me out with the following: I work on a boat and I'm looking for a Wi-Fi router powerful enough to reach from mid ships to below aft deck. The boat is made of aluminum and the distance is approximately 20 meters. -- Bart

A: Alas, the Wi-Fi Guru has not spent as much time on the high seas as he would like, save for the occasional childhood fishing trip, long before the advent of Wi-Fi. (Double alas, the Wi-Fi Guru is also no longer as young as he would like, either.) Not being familiar with typical boat construction, I am not sure how thick a metal barrier exists between decks. Three thoughts come to mind:

1.    It may not be good form for the Wi-Fi Guru to bite the hand that feeds him, but sometimes wireless is not always the best answer. Why not run a wired Ethernet cable between decks? Suppose you need wireless access from clients located on both decks. You have a wireless router on mid ship, and run a (weatherproof, marinized) Ethernet cable from this router down into the aft deck, where it connects to a second wireless router.Because the second router is hardwired to the first, it can be configured as a simple AP (access point) while the first router actually manages your Internet access. To configure the second router as a simple AP, you would disable its DHCP server and firewall, while configuring the wireless network as per your liking (SSID, e.g. "aft deck", and security settings). This way, aft deck clients would associate with your second router, but continue to receive their IP address and Internet access through your first router on the upper deck. Be sure to plug the Ethernet cable into your second router's "LAN" port (there may be several), and not the "WAN" or Internet port.

2.    If running a physical cable is not in the cards, you could accomplish a similar configuration using two wireless routers—one on each deck—and bridging them together via a wireless link. Doing this would work best with a very directional antenna connected to each wireless router, aimed precisely toward one another. The second (aft deck) router would be configured as a wireless repeater, either using WDS or repeater bridge mode (see next question) in DD-WRT. Frankly, you would need more gear to accomplish this compared to scenario 1, and it would be susceptible to more factors that could interfere with success.

3.    Finally, 20 meters isn't that far—a typical wireless router is rated to about 90 meters, albeit under ideal conditions. It is possible that a conventional wireless router outfitted with a strong antenna (rather than the cheap rubber ones they usually come with) will be good enough to power the signal through both decks. For more specific recommendations and links, I strongly recommend reading Wi-Fi on a Boat at Wireless Wiki.

Q: In your January 2007 article, DD-WRT Tutorial 5: Wireless Repeater, you say: "At the time of this writing, wireless repeater mode does not yet function in bridged mode. This means that...clients connected to your DD-WRT repeater must be inside their own subnet, preventing them from seeing clients connected to the host AP." Do you know with the release of v24 Final, if this has changed? Can I now set this up and function in bridged mode? That would be my ideal configuration, but....I have no idea how to set that up. – Tom


A: Times change. And yet, the more things change, the more they stay the same. To put it another way, the answer is “yes—maybe no.” In earlier beta versions of DD-WRT V24, wireless repeater mode worked only in non-bridged mode; therefore, clients connected through the wireless bridge could not share the same subnet as the primary router. With the release of V24 final, it has been reported by users that bridged repeater mode does work. Yay.

Last month, the DD-WRT people released the first update to V24, SP1. It is now reported by users that bridged repeater mode does not work. Yikes. Conclusion: it sounds like you should be able to create a wireless repeater bridge using V24 final but not SP1. The process itself should be about the same as in DD-WRT Tutorial 5, except that you will click to enable bridged mode. This will disable the DHCP server on your secondary router, since DHCP assignments will now originate from your primary router. Although our tutorial has not (yet) been updated to describe repeater bridge mode in more detail, you can read DD-WRT's wiki writeup.

Q: I am brand new to flashing firmware—DD-WRT and such—and quite intimidated. Can you please clarify getting new firmware onto the Linksys? –- a. rose


A: Great question. Technical tutorials often must make some assumptions about what information a reader may or may not already be comfortable with, but sometimes we assume too much. Let's tackle your questions one by one:


1.      Is the computer I'm working on that will flash the Linksys firmware supposed to be connected to the Internet?  I understand I should disable the wireless adapter. Before starting the flash process, you will need to download the binary file for the new firmware. For example, see our earlier story for help choosing which firmware binary to download for your model of router. Once you have downloaded the firmware file, you no longer need to be connected to the Internet. Indeed, you will not be connected to the Internet once you disable any wireless adapter and plug your laptop into the router you intend to flash.


2.      What is meant by “changing computer IP address to match Subnet of Router.”  How do I change my PC’s IP address?It may be best to simplest to let your network configuration be configured automatically. First, be sure to reset your router to factory default settings. You can do this by performing a hard reset, or pressing the "hidden" reset button on the back with the tip of a pencil for 30 seconds. This will cause the router to reboot. When you connect your PC to the router (see below), it will be assigned an IP address.

3.      Is the router firmware flashed with software already downloaded from DD-WRT?  Or is this done while connected to Internet?To clarify again, you will first download the new firmware and then disconnect from the Internet. The file you download will end in .bin, and this is what you will later send to the router.

4.      Any other critical issues to flashing the router firmware?  I've carefully ready all the warnings and requirements to match up router versions with firmware versions.

  Absolutely—be sure you have downloaded a firmware file compatible with your model of router. Also, disconnect any other network cables from your wireless router before performing the flash, just to be on the safe side. Note their locations so you can re-connect them after verifying a successful flash.

5.      Page 1 Router Setup says "Connect a wired PC to the DD-WRT router."  I guess firmware must have already flashed and "Wired" to what? PC Ethernet wired to router, or PC wired to ISP and Ethernet wired to router?Assuming you have downloaded the firmware file from the Internet, you simply want to connect an Ethernet cable from your PC to the router you want to flash. That's it. Neither your PC nor the router should be connected to anything else. Be sure to plug the cable into one of your router's "LAN" ports (usually marked as such).

Finally, you may remember that in our previous episode, a reader named Nikki stumped the Guru with a question about why shutting down her wireless client PC would disable her whole wireless network. A very insightful reader named John S. sent us this thought:

I think I have an explanation for Nikki's connectivity question from your column of July 11. I suspect that Nikki's problem is DNS-related. The laptop is probably running a DNS server (either legitimate or malware) that is advertising itself as the authoritative DNS server for the domain. When it powers up, other machines will immediately begin using it as their primary DNS server. Then, when the laptop shuts down, the other machines lose their DNS server and (from the user's perspective) their network connection.

Solution: Find and eliminate the rogue DNS server process on the laptop and the problem will go away. The other option is to assign a fixed DNS server (the local router) to the other machines on the network— but only if they are not portables that access other networks.

John's answer makes very good sense. Nikki says that when her network was setup, originally all clients worked fine, until later one of her laptop clients began exhibiting the "network killing" behavior. Indeed, it sounds as if this laptop may have been infected by malware. Nikki's best bet would be to run an anti-virus and anti-spyware scan on the troublesome laptops that cause this behavior. And thus concludes another episode of House...err, the Wi-Fi Guru.

Aaron Weiss is a freelance writer 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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