Ask the Wi-Fi Guru, Episode XVI

By Aaron Weiss

June 09, 2009

This month our Guru covers a lot of ground by answering questions related to bridging with open source firmware, such as DD-WRT and Tomato, as well as queries about boosting throughput for older routers and clients.

awhead.pngLast month, we celebrated the arrival of spring with a warning about how leaves can affect your wireless signal. With summer temperatures rising, Mother Nature isn’t done with us yet. Can heat and humidity affect your wireless network? Many anecdotal reports suggest increased problems with wireless links in hot and humid conditions. To be fair, it’s easy to sympathize with your router­­­—after all, who does like working in that kind of weather? But is there anything to these claims?

In very humid conditions, there theoretically could be enough moisture in the air to absorb some of the wireless signal. But RF experts tend to doubt the effect would be very strong unless your router is literally inside a cloud. Generally speaking, the longer your wireless link, the more likely it may be affected by humidity.

But perhaps a more common problem in summertime conditions is simply overtaxing the router. Consumer-grade routers don’t have cooling fans, but they do heat up. (Especially if you use a firmware like DD-WRT and crank up the output power.) Their innards are made up of relatively cheap circuits and connections. Hot and humid conditions could cause all sorts of wonky behavior with a router, from overheating the processor to moisture affecting internal contacts. A cool and dry router is a happy router.

Q1a: How do I access my bridged router since it doesn't appear to have an IP?  The whole system works fine, but I'm just concerned about if I to need to change the WEP key or something, how could I?—Randy

Q1b: I have successfully converted the WRT54G router with DD-WRT firmware v23 and converted it to be used as a wireless bridge as per your article and it works great. However now when I type 192.168.1.1 I get my primary router login page, how do I access my Linksys DD-WRT router again?—Izad

A: A question so nice, our readers asked it twice. Actually, more than twice. Both Randy and Izad ask about the same conundrum, one that naturally comes up often. But first, some background.

Randy and Izad have both set up a second router in their network, and using a firmware like DD-WRT (or possibly Tomato), have configured this router as a wireless bridge. In this configuration, the bridge allows wired network devices (like PCs, printers, and gaming consoles) access to the wireless network. The wired devices plug into the second router, and the second router obtains its network connection wirelessly by acting as a client to the primary router.

Assuming a default configuration, network IP addresses are being assigned by the primary router’s DHCP server. The secondary (bridge) router simply passes the DHCP communications to the wired clients. But what about the secondary router itself? How, Randy and Izad both ask, can the clients now access this router, for example to load its administration interface?

The IP address of the secondary router is determined by its “LAN IP address,” which you will find in the settings in both DD-WRT and Tomato. Assuming everything is default, this will probably be 192.168.1.1. But the LAN IP address of your primary router, assuming it is also default, may very well also be 192.168.1.1. Uh oh.

Before completing the bridge by joining the wireless network with your secondary router, you’ll need to manually configure the LAN IP address so that is compatible with, but does not conflict with, your LAN.

Suppose your primary router has the LAN IP of 192.168.1.1, and its DHCP server is configured to hand out addresses between 192.168.1.100 to 192.168.1.150. In that case, you could safely configure the LAN IP of your secondary router to 192.168.1.2 (or any other address not inside the DHCP pool).

By doing this, and then enabling the bridge by joining the secondary router to the wireless network, you now have a compatible IP address with which to address the secondary router.

A related question that sometimes comes up is, how would you access the secondary router from outside the network? Most routers let you enable a feature called “remote administration,” which lets you connect to the router from elsewhere on the Internet. But this won’t work for reaching the second router. To find the answer, rewind to an earlier episode of the Wi-Fi Guru (scroll down to the second question).

Q: I have some wired devices (an older iMac, a network printer/scanner and an NAS) in the first floor of my office, and I want to connect it to the Internet, which is provided by a router in the lower floor. I don't want to run a cable from one floor to another, so I want to connect the first floor devices to a wireless router (that has some network ports), and connect that router to the one on the lower floor, via Wi-Fi. From what I read, I can do this with a DD-WRT wireless bridge, right?

One question though: the DHCP is not enabled, and I want to keep it that way. If I assign the IP addresses manually, will the wireless bridge still work? – Jose

A: This is an excellent way to use a wireless bridge—to connect a second LAN to your primary LAN, using a wireless link rather than a cable to bring them together. Note that when you’re connecting multiple Ethernet clients to your bridge, you want to be using the most current versions of open source firmware for your router, be it DD-WRT or Tomato, among others. Some older firmware could only support a single Ethernet client on a bridged router.

In your case, you manually assign static IP addresses throughout your LAN, and so you have disabled the DHCP server on the primary router. This should not be a problem at all. In fact, read the above question and answer first—you will want to assign a static LAN IP address to your bridged router. Go ahead and configure static IP addresses for your clients—just be sure that they are on the same subnet as your primary router. So if your primary router is 192.168.1.1, then assign addresses in the 192.168.1.x range.

Of course, you don’t want the secondary router to run a DHCP server, either. Depending on your firmware, configuring bridge mode might automatically disable the DHCP server, but check to be sure, and if in doubt disable it yourself.

Q: I have an old Apple desktop and a G3 iBook 700, both running Mac OS 10.2.8. The iBook has an AirPort card in it, which runs 802.11b and connects to my D-Link DI-614+ router. Even though I only have 802.11b devices (also a wireless printer), I am considering upgrading my router to D-Link's DIR-655. I am considering this because I am hoping maybe the new router will (a) have a bit more range, as I would like to be able to wirelessly surf while sitting on a swing in my front yard; and (b) provide better download/upload throughput. I am supposed to be getting 15mbps/2mbps download/upload. When the router is connected I get upload speeds of between 200kbps-500kpbs. When the router is disconnected I get upload speeds of between 1600kbps-1700kbps!

If my range isn't increased with the new router, can I use my old wireless router, the DI-614+, as an access point to increase range?—Elizabeth


A:  Slow speed and limited range can be caused by a variety of factors, but the first red flag in this case is running a wireless-B network. The 802.11b technology is rapidly becoming the VCR of Wi-Fi, something quickly receding into the annals of history.

Your slow upload speed relative to a direct connection through the cable modem could be caused by a weak wireless link. 802.11b will throttle the speed down dramatically with modest degradation in link quality—in other words, it is not that robust compared to newer wireless technologies.

But, if you’re seeing full signal strength when your upload speed remains slow, my next thought would be whether you are using wireless security. On a b network this would mean WEP encryption, which can impose a significant penalty on link speed, especially with an older router that has a slow processor.

The D-Link DIR-655 is a draft-n router, which means it is (at least) two generations ahead of your b router. Running with g or n clients, the DIR-655 would certainly be a big step up. Without knowing more about your situation it is difficult to predict whether the new router would reach your front yard swing, but the chances are a lot better than with what you have now.

But…there is always a “but.” Running a draft-n router with wireless b clients is like running a BMW with three wheels. Or flat tires. The n router will have to make significant compromises to adapt to the b clients, which may undermine many of its next-generation advantages. Furthermore, if you did add a g or an n client to the mix, continuing to keep b clients on an n network will probably compromise the performance of the faster clients.

This will come as no surprise to longtime readers, but I would instead recommend a router that supports a firmware, such as DD-WRT or Tomato; the WRT54GL is great example. As an 802.11g router it will support both b clients and, if you upgrade, g clients. Flashing the router with replacement firmware will provide more options for tweaking its performance.

Your best bet to connect your iBook from the front yard with a g router is to upgrade the AirPort to a g card. To extend your wireless network using the DI-614+ as an access point would require creating a WDS link between it and the new router—unfortunately, the DI-614+ does not support WDS (as far as I know), so it cannot be used in this arrangement.

Aaron Weiss is a freelance writer, author, and Wi-Fi enthusiast based in upstate New York. To submit your questions to the Wi-Fi Guru, simply click on his byline (above) and put "Wi-Fi Guru" in the subject line. Click here to read last month's column. For more by Aaron Weiss, read "DD-WRT Tutorial 3: Building a Wireless Bridge." For definitions of unfamiliar term, visit our searchable glossary.

Originally published on .

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