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Comcast DNS servers are dropping constantly (75.75.75.75 and 75.75.76.76)

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Message 1 of 27
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I work in IT and it is abosultely infuriating that there appears to be no way to get Comcat/Xfinity to acknowledge that the problem with their internet service it THEIR problem. 

 

Comcast has two default DNS servers 75.75.75.75 and 75.75.76.76 and they are both dropping at least 50 % of the time, they simply cannot handle the traffic. This has been sever for the last two days. I call the support line and went through the script with the help desk person there. Powercycled everything, isolated down to just the Comcast Modem using two different computers on two different operating systems and the results were always the same....

 

Both Comcast DNS servers are not able to handle requests. 

 

To drive home the point, Google has two public DNS servers, 8.8.8.8 and 8.8.4.4 both of which have a 100% response capability. For the last two days I have had them programed so that I can use the internet and all is working fine. 

 

Like I said before I work in IT, I found a problem, and I am trying to report it. I have a work around, but other non-IT customers are being left frustrated. Please get the word to Comcast to fix their DNS servers.

 

Picture for details (7/23/13 noon in Minneapolis)

http://i.imgur.com/W5WYcDI.png

 

 

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Posted by
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Message 2 of 27
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Solution

I would suggest also the opendns servers

  • 208.67.222.222
  • 208.67.220.220

to go along with the google dns servers.  I am using both, with no packets dropped.

26 REPLIES
Posted by
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Message 2 of 27
117,083 Views
Solution

I would suggest also the opendns servers

  • 208.67.222.222
  • 208.67.220.220

to go along with the google dns servers.  I am using both, with no packets dropped.

Posted by
Connection Expert

Message 3 of 27
115,689 Views

It may help for you to post traces to both of those servers so that they could see which particular DNS cluster you are being directed to as those are *anycast* addresses.




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Message 4 of 27
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The other thing to keep in mind is that comcast may be throttling ping responses.  A better bet would be to run nslookup on 75.75.75.75 and try a bunch of different lookups to see if any of them fail due to a server timeout.  It's likely dns lookups will have a much higher SLA than ping responses.  IOW, I wouldn't base a DNS server's availability on ping...

Posted by
Connection Expert

Message 5 of 27
115,619 Views

FWIW, and AFAIK, they do rate limit / de-prioritize ICMP packet based ping / traceroute probes of their DNS servers.




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Posted by
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Message 6 of 27
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Thank you for your post!!

 

I just finally got everything installed and functioning this week- installation and 2nd appt to fix the installation and far too many hours on chat and phone (which never helped).

 

Now that I have Comcast Performance internet, I worked on the laptop and attempted to have the smart tv play Pandora.  So depressing as Comcast connection/lack thereof was so poor the spin cycle was longer in duration than any 2 min song.  Completely unable to listen to music or even watch a 22 min program in less than Over an Hour!   Infuriating!  This is a nightmare.

 

Sorry to yell - I wish we could all band together and create a solution.

Posted by
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Message 7 of 27
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btw -  meant to add that the screen shots are exceptional.  Would be great to hold Comcast accountable.

 

I'll continue reading, but if I manually change the DNS numerical values, is there anything else I need to perform ie. log out or do the settings automatically go into effect?  I've only seen these settings on my Samsung 'smart tv'  on the Internet Settings tab.  Where do I find them in my account/laptop?

 

Thank you!

Much appreciated.

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Message 8 of 27
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Hubby, who is an IT Tech like me, called Comcast tonight to make them aware of the DNS server problem and they told him that he had to pay for Signature Support. What?! He's doing THEIR work for them and then they want him to pay for it? They are completely ignoring the problem that obviously a lot of people (all their subscribers I assume) are having. They told him that "the system is down and call back during regular business hours". I mean, REALLY?! This doesn't just affect us here, it affects ALL OF their customers. There was nobody there who could do a simple PING. This is getting ridiculous. We have a lot of business clients who use Comcast as their service provider and I already know that on monday morning, our phones are going to ring off the hook because they can't get on the internet and do their work. Hubby changed our DNS to the public Google ones to "get us by" which seems to be working. When is Comcast going to do something about it? It seems like they are all incapable of a simple PING or unwilling to listen to us. This really sucks for all of us.

Posted by
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Message 9 of 27
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Thanks for posting this information.  I've been on tech support with Comcast 3 times this week and they haven't been able to solve my problem.  I was trying to use Google DNS a week ago for League of Legends because of issues I was having -- but I stopped using it when they had supposedly fixed their routing issues, and now my internet has been constantly disconnecting since then.  I just switched back to Google public DNS a couple hours ago and I haven't had a single disconnect since.  I will definitely be contacting them soon to let them know they need to get it together.

Posted by
Connection Expert

Message 10 of 27
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Really_ wrote:

btw -  meant to add that the screen shots are exceptional.  Would be great to hold Comcast accountable.


As stated pinging their DNS servers doesn't prove anything unfortunately..




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Message 11 of 27
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Message 12 of 27
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Message 13 of 27
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Tech came out today and resolved my problem. Turned out to be related to recent high humidity in the region.  Cable corrosion, in other words.  Cables were swapped out from the modem to my router and from the house to the central office.  Another tech came out about an hour or so after the first one left and did some work at the central office to strengthen the signal.  All is well here, never been better.

 

I had tried the different DNS servers and one of my co-workers thought maybe the modem needed a firmware upgrade.  My modem apparently upgrades it's firmware automatically.  Nonetheless, one of my suspected culprits was the recent weather and I was right.  I have to say, while I've wrestled with Comcast once or twice a few years back trying to get a cable card properly configured for my Tivo, they nailed this bugger on the head, quickly and efficiently.

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Message 14 of 27
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I have the same problem which just appeared recently "out of the blue" on my Computer... I believe you are absolutely right and these things usually turn on money? What do you think?

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Message 15 of 27
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IS IT COMCAST WHO WILL NOT FIX THE DNS SERVER PROBLEMS?

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Message 16 of 27
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Message 17 of 27
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So the dropped connection is not my Motorola SB6121 modelm that Comcast is telling me is the problem? I don't understand how we can pay for service and then not have it. This is very frustrating. I'm about to shell out another $80 for a new and different modem. But if this isn't going to fix the problem, I'll save my money and find a new provider.

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Message 18 of 27
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If you disconnect all cords and the power, this may solve the problem... It worked for me last week and It has been working since then... Good Luck...
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Message 19 of 27
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I tried this and it did nothing. But thanks for the suggestion!

 

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Message 20 of 27
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Just got off the phone with Comcast.  Reported the poor internet service, and lengthly wait times.  I reference the information you provided and they had no clue as to what I was talking about.  They sent me to the Signature service who gave me the same run around and told me I had to pay for them to solve THEIR server problem.  After going around in circles with them about my needing to pay to fix THEIR problem I took the advice of this BLOG and changed my DNS resolution server to 8.8.8.8.  Magically the problem disappeared and I am getting much better response time.

 

Thanks for your help.  The management of COMCAST needs to wake up to this issue.  Any suggestions how this might be achieved?

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Message 21 of 27
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I agree, I've been having the same issue and they have swapped out modems twice, sent out two techs, etc.  One thing that I have always used as an IT Professional myself is a tool called namebench.  It finds all the DNS servers, tests them, and gives you the optimal settings and lots of details.

 

 

The tool:  https://code.google.com/p/namebench/

 

For beginners:  http://macs.about.com/od/networking/qt/dns-faster-web-access.htm

and no, I don't use a Mac or Windows PC- All open source here, baby! lol

 

J

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Message 22 of 27
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According to my tests, as well as a namebench report, 222.222 - OpenDNS-2 is the fastest DNS server for the Houston, TX area.  Good idea to add it!

Posted by
Contributor

Message 23 of 27
110,114 Views

I believe comcast rate limits icmp packets to their dns servers.. simply pinging them wont do.. have you tried using dig or nslookup?

Posted by
Connection Expert

Message 24 of 27
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Rugburn wrote:

I believe comcast rate limits icmp packets to their dns servers..

 

Indeed they do.

 

have you tried using dig or nslookup?

 

FWIW, those tools won't measure resolution performance time, only whether or not names resolve at all. 


 




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Posted by
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Message 25 of 27
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EG wrote:

Rugburn wrote:
...

have you tried using dig or nslookup?

 

FWIW, those tools won't measure resolution performance time, only whether or not names resolve at all. 


dig comcast.net
...
;; Query time: 33 msec
...
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Message 26 of 27
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Thank you for this post.  I've had it with Comcast and will be switching internet company as soon as my contract is over.

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Message 27 of 27
106,052 Views

I am the most computer illerate person out there. I was having the same problem  and a problem with them resolving the problem. (Sorry).  I have norton antivirus and called them because comcast wanted to me to sign up for the signature service to repair. They gave me an answer and told me to call them back it was their issue not mine. I called them back and they still wanted me to sign up with signature service for them to fix. I copy and pasted this post while at the library to give it to my hubby to figure out. I am so infuriated that they could not tell me what steps to take to fix it. Unbelieveable. They told me that they needed to remotely access my computer and that required "signature service" and an additional charge. GRRRRR. They are sending out a tech tomorrow. Cancelling...thank you!