D-link DCM-202 Cable Modem

I recently moved and this meant that I had to replace the cable modem I was borrowing. I own a DI-524 Wireless Router that has been functional if not completely delightful. Let's just say I've had even more horrifying experiences with other routers. With that in mind I thought I would stay with the D-Link brand so that I would maximize the chance that my router would have no problem with the cable modem.

Sounds reasonable doesn't it? Now it's important to understand that a cable modem is not rocket science. I have a TV wire coming into my house and I want it to be an ethernet wire. It's really just a fancy converter from TV wiring to computer wiring. At least that's how it should be from the end user's standpoint. I plugged all the wires in the holes they fit in. And (after an excruciating experience with my ISP to get the MAC address and serial number, don't forget the serial number) voila! Internet! Yea!

That was no problem and I was happy to move on to the million other problems that plague my life. Maybe you plan to use your home's internet connection once a week or so for checking to see if the only other person you know with an internet connection has sent you some lolcatz. I, on the other hand, have a different agenda. The first thing I do when I get to work, is to log in to the computer at my house, which I then proceed to use all day. It is actually an important part of my job to be able to use the computer at my house from work to test how things at work look from some guy-with-a-cable-modem's house.

After a couple of days of operation as expected, suddenly, there was no connection. Hmm. I had been doing some exciting things with my server's configuration and figured that it was something I had done related to that. But when I got home, I found that all the computers inside the network were operating just fine. The server I had been connected to was waiting patiently for me where I'd gotten cut off. I simply had no connection to the outside internet. Finally I power cycled the cable modem and when it came back up, I had a connection again as if nothing happened.

I figured that was an anomaly, but the next two days, this happened again. Ok, this is *not* going to work out. I immediately ordered a new modem. But until that arrived, what am I going to do with the DCM-202?

I wondered if I could possibly figure out a way to achieve the effects of the hard power-cycle through software. Then we get to part two of why this cable modem is simply not ready to be a product that people pay money for. Although, as I've stated, cable modems should be something you don't have to know too much about, there is actually a service interface for this thing. By pointing your browser at 192.168.100.1 and using the username "dlink" and the password "dlink" you can access the modem's control center.

I don't want to digress into a review of Microsoft's Active Server Page technology, but let me just say this to everyone: DO NOT EVER USE ASP! Ever! Ever. Do you understand? Ever. It is only a good idea when you're contemplating suicide and you need some extra incentive. What this means to you, dear contemplater of buying a DCM-202, is that this interface was so massively fubar that it was comical, or would be if disconnection from the net didn't rob me of my sense of humor. So Firefox on Linux just renders this service interface as the trash it is. You can click on anything and you'll get the status. Nothing else works.

Here's where it gets interesting and a bit technical. Because I was highly motivated, I thought to try the Twibright Links browser and, incredibly, it was able to sort out what the links were supposed to do and it actually would let me click the reset button! Cool. So I could reset the modem without physical access. The next thing I did was fire up wireshark and I watched the packets that made the modem reset. I then was able to figure out the exact call that resets it. I set up a cron job to run a bash script that checks my connection and if it's dead, reset the modem. Here's the function that actually resets the DCM-202:

function reset_stupid_modem {
CMD="/usr/bin/wget "
CMD="${CMD} -O /dev/null "
CMD="${CMD} --tries=1 "
CMD="${CMD} --user=dlink "
CMD="${CMD} --password=dlink "
CMD="${CMD} --post-data=save=Save+%26+Reboot"
CMD="${CMD} http://192.168.100.1/goform/Cable "
echo ${CMD} >> ${LOG_FILE}
eval ${CMD}
}

Hopefully that can help someone while you wait for your new modem to arrive. But my advice is to simply avoid being the owner of one of these in the first place. I suspect it has overheating issues, I know its interface is awful, and unrecovered random service outages are completely unacceptable.