Mar 30
Comcast Blocking DD-WRT?
About a month ago, I received a notice in the mail from my ISP, Insight, with news that they had been bought-out by Comcast. They promised that there would be no changes in my service and the transition would be seemless. Everything would work as it had, except they would charge a little bit more. Great.
They’re in the midst of transferring services to Comcast, set to be complete sometime in April. Everything was fine on our end until our internet went out a few days ago. After a few hours of toying with it, I decided it had to be Comcast’s issue. I tried rebooting the router, renewing the IP, and even connecting my computer directly to the modem– nothing worked.
Finally, I called Comcast and talked to one of their “specialists” from Indiana (better than India, right?). He dialed into the modem, and was able to get a computer hooked up through the modem, but still not through the router. We made an appointment to have somebody come out.
Two days later, somebody from Comcast came out and tinkered with things for about an hour. With all of the toys in his magic bag, he still couldn’t get the router working. Moreover, we were able to hook up a different router, and that one worked. We chalked it up as a faulty router, and he was on his way. But something was still fishy.
We bought the router about 5 months ago, and everything had been working on it perfectly. I installed the DD-WRT firmwire for even more control. Everything looked good on it, except we couldn’t get an IP from the modem. After doing a little research, it seems that Comcast has some trouble with DD-WRT routers. The solution was to change the router’s MAC address from the default DD-WRT address to something else. Many users clone their laptop’s MAC, but I used one from an older router. A quick reboot afterwards, and we’re back up.
It’s hard to say whether it’s an incompatibility issue, or Comcast is actively blocking this alternative firmware. I’ve generally had bad experiences with Comcast, so I choose to believe the latter. Anyway, I’m glad we got things worked out, because I wasn’t too excited about going through the warranty process with Linksys either.
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April 5th, 2008 at 9:03 pm
They are probably looking for the MAC address of the client machine. If DD-WRT has the same MAC set every time someone installs DD-WRT there system may get confused if someone else is using it already.. Just speculation.
April 6th, 2008 at 6:46 am
I agree, this is probably the case. But the fact that it essentially disables DD-WRT router, the net-effect is equal to Comcast blocking it. Moreover, the technician had no experience with the problem, and had me convinced that my router had just gone bad. The fact that it should’ve “just worked”, and it has “just worked” for other ISPs, makes it a Comcast problem.
April 21st, 2008 at 3:29 pm
Interesting in that I had simular experience, Put DD-WRT on a spare
wrt54g. Swapped it out with my old befsr41. Nothing. waited hours and
cycled power etc. etc. Swapped the befsr41 back and connection was up again.
I believe that Comcast only has the MAC of my modem (my modem got changed
recently, and I watched the tech register the new modem MAC) in their system
but decided to change the MAC on the WRT54g anyway.
As soon as I did that, I had a DHCP lease, same ip as before.
(I used the MAC from the old befsr41)
April 23rd, 2008 at 4:16 pm
This just happened to me today. I put dd-wrt on my router about a month ago and it worked fine until this morning. Interestingly, I couldn’t even get a DHCP lease with my laptop wired directly to the modem until I called tech support.
After we got my laptop working I hung up and hooked the router up again…no DHCP lease. Cloned the laptop MAC address and everything works now.
By the way this page is the #1 Google hit for “comcast mac address blocking” right now.
April 23rd, 2008 at 5:23 pm
Thanks for the comment Chris. It sounds like we’ve really hit something. Is Comcast new in your area by any chance? I wonder if it is location-specific. I am in Urbana, IL.
April 24th, 2008 at 6:36 am
I’m in Sarasota, FL. I’ve lived in the same apartment for three years and have always had Comcast.
April 26th, 2008 at 8:55 am
Thanks for this post. I have Comcast, located in Chicago (Wrigleyville), and about a few weeks ago I started having issues with my router. I’ve had DD-WRT installed for almost a year now with no issues, but all of the sudden I had no connectivity, and could not figure out the issue at all. F#%@ comcast
July 14th, 2008 at 1:14 pm
I’m an IT professional and run a side biz servicing home users as well as small business in my area. Over the last week I have had 2 clients (both Comcast) contact me with the exact issue verbatim. One lcient uses a Linksys router the other Netgear (both manufacturer firmware). The solution was to clone their PC mac addresses in their routers.
When I signed up for Comcast over a year ago (and dropped Pay-T&T) I already had a Linksys router with Linksys firmware. I had to clone the PC mac address I used to set up my Comcast service to get my router to work. Later on I installed DD-WRT and still had to clone my Mac address. So the mac address cloning issue is not DD-WRT related at all as I had to clone it pre-DD-WRT and both of my clients recently (non DD-WRt) all of a sudden had to clone their MAC addresses.
Looking at the dates of the first posts here this leads me to believe Comcast is slowly but surely setting all their nodes to require the specific mac addresses of the PCs that users activated their service on. I’m guessing this is to exploit money from people making them believe they have to pay an extra $10-20 for Comcast’s home networking plan.
September 26th, 2008 at 3:05 pm
Comcast suddenly quit working with my dd-wrt router after it had been operational for nearly a year. No amount of changing MAC, cloning, etc. worked. Could still get a lease with any old computer - but not with dd-wrt, no matter what. Finally ended up putting stock linksys firmware back in place, which worked.
October 17th, 2008 at 7:11 am
Update: One month after putting the stock linksys firmware back in place, the router can no longer get a DHCP lease. Plug in the computer directly — get a lease. Clone the MAC, plug the router into the modem — no lease.
October 19th, 2008 at 2:25 pm
Update: Comcast is blocking uDHCP request packets based on packet length. The only solution I found was to use the tomato firmware on the Linksys router, and check the “short DHCP packet” option. Comcast now grants leases to the router.