I'm a Comcast customer, and last night all of the computers connected to my wireless network lost their Internet connections. The PC connected directly to my router, though, worked without a problem.
I tried turning the router on and off, but that didn't solve the problem. I tried resetting it. That didn't work, either. I upgraded the firmware. Still no go. I even tried using a different router, and that didn't work, either.
Why, I wondered, was my wired PC working, but not my wireless ones? I looked at my wired PC's TCP/IP settings, and found the answer immediately: Instead of using Comcast's DNS servers, I was instead using OpenDNS's servers, a free service from OpenDNS. I had previously found OpenDNS service to be superior to Comcast's. Clearly, the problem was with Comcast's DNS servers, because my wireless PCs were still using Comcast's DNS servers.
The fix was simple: Tell my Linksys WRT160N router to use the OpenDNS servers. Once I did that, everything worked like a charm. Here's how to do it on a Linksys router; the instructions will vary according to your router make and model:
1. Go into your router's configuration screen. For Linksys, that means going to 192.168.1.1, and typing in your user name and password. For most Linksys routers the default user name is admin and there's no password.
2. On the main screen, go to the Static DNS boxes. In Static DNS 1: enter these numbers: 184.108.40.206. In Static DNS 2: enter these numbers: 220.127.116.11. You can see what it should look like, below.
3. Click Save Settings. After that, I was able to get onto the Internet from all of my PCs, because my entire network, not just my wired PC, was now using the OpenDNS DNS servers.
If you don't have a router, and only have one PC connected to the Internet via Comcast, you'll have to change the TCP/IP settings on that PC to use the OpenDNs DNS servers. How you do this varies according to whether you use a Mac, PC, or Linux, and the exact version of your operating system.
In Windows Vista, for example, right-click the network icon in the system tray, select Network and Sharing Center-->View Status-->Properties, highlight Internet Protocol Version 4 and click Properties. On the General screen, select Use the following DNS server addresses, and in the Preferred DNS server type in 18.104.22.168. In Alernate DNS server type in 220.220. You can see what it should look like, below. Click OK.
There's no guarantee these steps will fix the problem for you. But it did the trick for me, and I plan on never using Comcast's DNS servers ever again.