A Little Off Code, Computers, Photography and Guns

3rd Party Router Firmware

Until Monday I'm without any kind of proper internet connection which means until this point I've just been using my phone to browse the internet and chat with friends, which is frustrating to say the least. This prompted me to do a little more research on 3rd party firmware for wireless routers.

The first project that comes to mind is obviously DD-WRT^[1] the most popular and probably the most powerful of them all right out of the box. Before I moved here I researched and purchased a new router to use at my new place. I stumbled upon a Netgear router which seemed to match all the features I needed at a reasonable price. I've never really been a huge fan of Netgear routers but I checked that it was compatible at least with DD-WRT before I bought it. The router I'm talking about is a Netgear WNR3500L^[2] which includes:

• 802.11n WiFi
• 4x 10/100/1000 Ethernet ports
• 1x USB 2.0 port

I think grand total it was ~$90^[3]. Anyway first thing I did was install DD-WRT which is standard practice for me. Ran exactly as intended except when I tried to set it up to act as a wifi client which failed miserably, I never did figure out how to make it do what I wanted. Everything else worked as intended. But I recently discovered a new firmware I wanted to try, which was Tomato^[4] another open-source project like DD-WRT.

Tomato is essentially a watered down version of DD-WRT. I think the only useful feature it's missing that DD-WRT has is virtual wifi interfaces, but that's not such a big deal. On the other hand though Tomato has the most polished bandwidth monitoring features of any other project I've ever seen or used. DD-WRT has essentially the same feature but it's much weaker and not nearly as thought out and well designed as Tomato's is.

My main gripe with Tomato is it's lack of community support. DD-WRT is so popular that just about any router you can get your hands on has a forum post somewhere about someone's woes with installing something on it and getting it working the way they needed it. Tomato isn't quite the same way. Also it appears that Tomato mostly only supports broadcom chipsets which is what my new router has.

Well anyway I just decided to download the latest version and try it out. Bad idea. I hadn't really considered that putting firmware on it that doesn't support USB would brick it. Figured USB just wouldn't work, WRONG. Got the firmware uploaded and reset it nothing. Nothing at all. So first thing I did was look up instructions for uploading a new firmware (one that I knew worked) using tftp. No luck, the router responds to pings for about 2 seconds immediately after booting but then ceases to respond. This was a good sign at least, means some basic features were still working properly. Also discovered that because Windows 7 implements CTCP instead of a simpler TCP protocol this breaks most ability to upload new firmware via tftp. So I downloaded an atftp.deb for my linux box and that didn't work either.

Eventually I stumbled upon an article about using a USB-TTL cable to unbrick the router. This article was mostly useless because all they were doing was using a USB serial adapter and dissecting the cable to work with the serial connection on the routers board, which I could just as easily have done with my arduino. But hidden deep in the comments was a far simpler trick than that. Only thing I needed to buy was a torx screw driver set to get the thing open. I looked up the chip used for storing settings and found that there were two pins on it that could be shorted to erase nvram (the structure responsible for storing all the router's settings).

So I busted open the router and proceeded to power on the router while shorting the two pins. No effect. I tried powering it on and then shorting the pins. No effect. Finally I tried shorting the pins exactly when the router responded to pings during that 1-2 second window. Success!

Then I fired up tftp and uploaded a modified version of Tomato to support USB and vaula! Tomato works properly on my router now. As well as the wifi client mode and wifi bridge mode. Anyway that occupied several hours of tinkering where I would have otherwise been bored out of my mind.

1. DD-WRT Firmware [↩]
2. Netgear WNR3500L [↩]
3. Newegg.com: Netgear WNR3500L [↩]
4. Tomato Firmware [↩]