Backup of David's Livejournal

Open-Source Rocks - DD-WRT vs. Comcast Edition

I've got an old home WDS system set up made up of two Linksys WRT54G gateways. It's awesome. I love Linksys for allowing the WRT54G to be "the first consumer-level network device that had its firmware source code released to satisfy the obligations of the GNU GPL."

The WRT54G wasn't configured to build a Wireless Distribution System, but the hardware was capable of it. I installed DD-WRT and followed an online recipe that gave me the configuration I needed:

  • One gateway in the office upstairs for all the local devices and the wi-fi devices.
  • One access point in the family room downstairs to extend the range of the network and for local (media) devices to speak to each other at high speed directly across the local switch, while still getting out to the internet when necessary.
This all worked great with my old DSL connection. But recently, we migrated from DSL to cable modem, and the new provider was Comcast. The Comcast technician came over to hook us up, but had a little trouble getting the computer online.

I had a sinking feeling that it was the WDS system I had in place. After a few early attempts, the service guy listened to me, and removed the WRT54G from the equation. Sure enough, when the cable modem was connected directly to the computer, the computer found the internet right away.

I was pretty upset that my WDS might not work anymore. I searched the web for terms that included DD-WRT and Arris and Comcast. Sure enough, half the hits I found indicated that the devices were simply incompatible. Wouldn't work.

But a few of the others suggested I set the local gateway to clone the computer's MAC address. That seemed like an advanced and bad thing to do, but if they were right, and Comcast had blacklisted the default MAC address that  DD-WRT uses, it was worth a try.

I navigate to the gateway's administration page expecting to have a lot of trouble, but it turns out to be really easy!

So I told the gateway to clone the PC's MAC address, crossed my fingers, and ... it worked!  It turns out Comcast was blacklisting the default MAC address the gateway uses!  W00T!  My home network is back in business.

... Until I upgrade to 802.11n.

(This is posted to add just another reference page on the net where a fix was found.  Hope it helps somebody.)

Tags: geek, solved


 halophoenix on Mar 13th 2009 at 4:38 PM
Very very nice! I've been using Tomato on my old WRT54G, and haven't looked back. I'm actually kind of thrilled to see a use case of MAC address spoofing that isn't designed to sneak onto unwitting wireless networks that filter access based on them. Nicely done! ;)

 sjonsvenson on Mar 13th 2009 at 9:26 PM
confused. A MAC address is linked to the network 'card' isn't it? But if you have to clone the MAC does that mean you cannot swap another coputer without spoofing the MAC? Or has Comcast got a list of all the MAC addresses that Linksys used?

 dblume on Mar 13th 2009 at 10:48 PM
I haven't bothered to fact-check this, but I believe that by default, DD-WRT uses a hard-coded default MAC address. I have no idea why. I'm sure there was a reason. This, for obvious reasons, caused trouble for ComCast, who proceeded to blacklist that default MAC address.

 (no name) on Jun 25th 2009 at 5:11 AM
Though I could connect using my dd-wrt flashed router, the speed was about 1/10 of what I got when connecting directly to the modem. The MAC address cloning worked exactly as described, and my speeds are normal now. I sure would've hated to give up on dd-wrt.