The content of this blog is my personal opinion only. Although I am an employee - currently of Nvidia, in the past of other companies such as Iagination Technologies, MIPS, Intellectual Ventures, Intel, AMD, Motorola, and Gould - I reveal this only so that the reader may account for any possible bias I may have towards my employer's products. The statements I make here in no way represent my employer's position, nor am I authorized to speak on behalf of my employer. In fact, this posting may not even represent my personal opinion, since occasionally I play devil's advocate.

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Wednesday, September 28, 2011

Xfinity failing every afternoon 2:30-6pm approx; comcast DNS problems fixed by google

Xfinity failing every afternoon 2:30-6pm approx; comcast DNS problems fixed by google

My comcast internet cvonnection was failing regularly, every weekday, starting at approximately 2:30pm, lasting until 6 or 7pm. This started happening shortly after labor day.

I conjecture that this was probably happening because schoolkids were getting off school (which in my area happens circa 2:30pm) and starting to use the net.

The failures were accompanied by error meessages of the form "DNS error... DNS lookup failure... Error 105 net:ERR_NAME_NOT_RESOLVED". That error message was from a Windows 7 machine. I also regularly have a Vista machine and an Apple Mac connected to my home network. The Vista machine occasionally worked when the Windows 7 machine did not, and the Apple Mac more frequently worked; but all regularly failed about the same time in the afternoon. Yes, I tried powering off/disconnecting/connecting only 1 machine at a time. Not a cure.

Coincidence? I think not.

I reported the problem to Comcast, who very quickly sent over a "cable guy" who apologized that my 7 year old Linksys cable modem had not been replaced. So now I have a new SMC cable modem, and the net performs much better, up to 10X faster than in earlier speed tests. This is great!

But, it did not fix the DNS problem.

My Windows 7 machine (actually, the Windows 7 laptop my employer gave me) still got DNS errors between roughly 2:30 and 7pm.

My Vista machine sometiimes ran when the Windows 7 machine failed.

And the Apple Mac seemed nearly always to work, failing only occasionally.

But the Windows 7 machine reliably failed between 2:30 and 7pm.

OK, so I get more serious. I check the DNS settings. Finally, I do what I should have done in the first place: I switch the Windows 7 machine DNS server frm "automatic", i.e. from comcast's DNS servers, to Google's DNS servers, and

Fixed! :-)

Conclusion: Comcast DNS servers have problems. Particularly when the kids get home from school.

But I'm happy that I got a new, faster, cable modem out of this. And it is interesting that different machines with their different OSes behaved differently. Different timeouts (DNS settings that don't appear at the usual configuration places)? BTW, the machine that failed most often is the fastest machine by far.


BTW, I did try fixing DNS earlier, to no avail. OpenDNS did not seem to work. But I wasn't that serious, so I did not try all possibilities. It is possible that both the cable modem needed to be upgraded, AND the DNS needed to point away from comcast's DNS servers.

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