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Comcast DNS servers are dropping constantly (75.75.75.75 and 75.75.76.76) ... Revisited 2020

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Comcast DNS servers are dropping constantly (75.75.75.75 and 75.75.76.76) ... Revisited 2020

This post references a previous question post from 2013 of the same subject title minus the "... Revisited 2020".  I tried to post new to that thread but apparently that is not possible, or not easy through Xfinity's interface (I'm a little new to RSS feeds).  There may be a proper way to reference previous feeds/postings in a new posting but apologies I do not know that procedure.

 

It would appear that this issue is happening again, for my locality at least.  This involves the same DNS server IP addresses as in the previous post and in the subject of this post, normally set automatically from configuration info sent from Xfinity servers.  This time it is early 2020.  This started happening recently, in the last few months, may have started end of 2019 but I don't recall for sure.  It happened again this morning.  I will have a fully-functioning internet connection for hours when suddenly the browser is unable to resolve any hostnames.  Then I reboot my MG-7550 cable modem/router/access point over and over every minute or so, each time apparently connecting successfully over the Ethernet via DHCP info but not seeing the DNS server IP addresses get populated from the Xfinity server information.  After about 5-10 minutes, I get the DNS server info and can resolve hostnames again.  This happens every week or two any more.

 

Given that I retain the Ethernet connection but lose the hosname resolution ability I have trouble believing that ths is solely a connection/wiring issue.  Otherwise why would the Ethernet connection be successful but the DNS server info not?  It really seems like the DNS server(s) are being rebooted for whatever reason.  It doesn't show up in the Xfinity online outage indicator as an outage in the area.  No outages are reported.  I just chatted with Xfinity support and was basically teaching them the basics of Ethernet connections and DNS servers.

 

One thing about the previous occurrence of this type of issue in this area (central Pennsylvania locale specifically in this case), there was a bunch of talk about ping activity being moderated by the Xfinity servers.  However, I didn't get the impression that the person who reported the original occurrence was basing the report solely on the ping responses, rather the problem that triggered the issue was more likely similar to mine, sudden cessation of hostname resolution for 5-10 minutes.  My impression was that the ping utility was just being used as a tool to diagnose the issue.

 

FWIW, I am an electrical/software engineer with many years of experience designing Ethernet circuitry for single-board computers and subsequently programming the embedded interface, in "Internet of Things" sorts of applications.  I may still be missing something here, but I am just giving my credentials for reader reference.

 

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Re: Comcast DNS servers are dropping constantly (75.75.75.75 and 75.75.76.76) ... Revisited 2020

The problem may lie between your modem / gateway device and the Comcast system. Many times general connectivity problems appear as generic DNS problems when they are not.

 

What do the modem's signal stats look like ? Try getting them here; 

 

http://192.168.0.1 The default username is admin and the default password is motorola

Please post the *Downstream Power Level*, the *Upstream Power Level*, and the *SNR* (Signal to Noise Ratio) numbers.




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Re: Comcast DNS servers are dropping constantly (75.75.75.75 and 75.75.76.76) ... Revisited 2020

I agree with @EG , it's probably not an actual DNS issue. You can change the DNS servers pretty easily to verify:

 

Google DNS

Preferred: 8.8.8.8
Alternate: 8.8.4.4

 

OpenDNS

Preferred: 208.67.222.222
Alternate: 208.67.220.220


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Re: Comcast DNS servers are dropping constantly (75.75.75.75 and 75.75.76.76) ... Revisited 2020

It sounds like you are enough of a geek to do this:

- Buy a Raspberry Pi, take your pick from a $10 single core Zero W all the way to a $40-$50 quad core 4B.    I use an old 2B.   There's more than enough horsepower in the Zero W to handle the workload.

- Add the appropriate case + power supply; expect to spend another $10-$20 here

- Add the smallest Micro SD card you can find; you don't need more than a 4GB device but those are soooo hard to find these days; $10? Maybe a little more.

- Get the appropriate HDMI cable.   The Zero W uses a micro HDMI whereas the larger Pi uses a standard HDMI cable.

- Find an old USB keyboard/mouse to use for the initial configuration; $10 otherwise

- Install Debian

- Configure a caching name server using well known name servers like 8.8.8.8 for the forwarders

- Disable the DHCP server on your router.   It still needs to be a DHCP client to route properly but you do not care if it never, ever, gets a response from Comcast DNS servers again and you certainly do not want it to tell your systems to use 75.75.75.75 and 75.75.76.76 for name servers.   

- Enable the DHCP server on your new system.  Tell your clients about the correct router and perhaps ntp servers, and tell them to use your new system for name resolution.

 

Total cost?  $20-$100.   The fact that you never have DNS problems again?   Priceless.  🙂

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Re: Comcast DNS servers are dropping constantly (75.75.75.75 and 75.75.76.76) ... Revisited 2020

@person00001 

 

The commentary from the above poster is assuming that it is indeed a DNS problem..

 

Please post the requested info.



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Re: Comcast DNS servers are dropping constantly (75.75.75.75 and 75.75.76.76) ... Revisited 2020

I don't often check my Xfinity e-mail inbox, and since that is the only place Xfinity was sending any communications other than billing stuff, I just got the response notifications (yes, I finally found the "forward e-mail" setting).  My follow-up is primarily for the Xfinity official response but also serves a general response.

 

I believe I was wrong about it being a DNS issue. It probably was a connection issue.  The responses got me thinking about my smartphone, which I had not paid enough attention to with respect to this issue.  I seem to recall that, even with the VPN active and linked to the internet through WiFi and to a different server, it also lost name resolution, which it shouldn't have done if it was solely with the Xfinity DNS server(s).  For all I know, the server to which we customers connect and the DNS server may be the same machine at Xfinity.  You guys know the Xfinity IT infrastructure, I sure don't.  Of course *technically* if there is no connection to the internet then there is probably also no DNS server either, at least as far as those downstream are concerned, but that's neither here nor there.

 

For what it's worth, my intention was to convey an appropriate level uncertainty in my post, but needless to say I was becoming very frustrated with my internet randomly becoming unusable.  I do tend to feel it necessary to make assumptions when I spend half an hour talking to Xfinity support with no progress towards resolution and there is no outage indication per the Xfinity web site so I am left feeling completely helpless. More than anything I wanted to put this out there in case others were experiencing a similar issue, as it appeared to be remarkably similar to the previous forum post which I reference in mine, and the similarities to the existing post were the two DNS server IP addresses.

 

However, reconsidering my post, I believe that I was trying to be too specific. The far more relevant question was whether the issue was on my side or Xfinity's. If the issue occurs again, I will attempt additional tests to determine if the issue is on my end, taking the suggestions presented here into account. All I really I need to do is determine with reasonable confidence whether the issue appears to be on my side or Xfinity's. If it appears to be on Xfinity's side then Xfinity would diagnose the cause of the issue, not me. I hope that I did not offend any in attempting to identify a cause so specifically with limited information.

 

Incidentally, apparently the same behavior occurred this past week on Wednesday, March 4, a bit after 2pm Eastern time. This time the Xfinity website did indicate an outage for my area. There was no visit to my property or service truck in the area, visible to me. I have not made any changes on my end whatsoever. It may have been a completely different cause, but I can't help but wonder.


P.S: Please reconsider using the wording, "sounds like you are enough of a geek".  For one thing, not everybody who is technically-minded appreciates being called "geek", or "nerd" for that matter, whether it is intended positively or negatively, and for another thing, it sounds a bit patronizing, as if you are talking down to someone that you consider less intelligent.

 

P.P.S: If the EG responses are not the official Xfinity responses, please disregard this part.  If they are, it could have sounded a bit more like the issue might have actually been on Xfinity's end and therefore a little more concilliatory, and not so much like debunking my attempt at identifying a cause. I know that technically-inclined people including myself tend to focus on thinking about the problem/solution at the expense of the interpersonal aspect, so I don't fault anyone for it as a person.

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Re: Comcast DNS servers are dropping constantly (75.75.75.75 and 75.75.76.76) ... Revisited 2020

My responses are my own. I am not a CC employee. That said, I had asked you to post that requested information in order to help determine the state of your connection quality / if the RF signal stats are in or out of spec, or are marginal. FWIW, you still haven't posted them.



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Re: Comcast DNS servers are dropping constantly (75.75.75.75 and 75.75.76.76) ... Revisited 2020

FWIW, I have no reason to believe that representatives of Comcast routinely read this forum.     If you read through the posts you will see very few responses from anyone identified as a Comcast employee.   There are, however, a few select individuals that appear to have the ability to escalate a thread to Comcast's attention but it seems that rarely happens.   

 

That being said, check your signal levels and check your error counters on the modem.   In the few months I've been following this forum I have observed that most problems are related to poor signal quality to/from the modem.    I do not know why name resolution (DNS) is more sensitive to signal quality but that seems to be the case, or at least that seems to be the first item people report as a problem with their connection.

 

Good luck!

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Re: Comcast DNS servers are dropping constantly (75.75.75.75 and 75.75.76.76) ... Revisited 2020


@cxrider wrote:

 There are, however, a few select individuals that appear to have the ability to escalate a thread to Comcast's attention but it seems that rarely happens.   


That must be your opinion.. How long have you been here.. It's not as rare as you say..



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Re: Comcast DNS servers are dropping constantly (75.75.75.75 and 75.75.76.76) ... Revisited 2020


@EG wrote:

@cxrider wrote:

 There are, however, a few select individuals that appear to have the ability to escalate a thread to Comcast's attention but it seems that rarely happens.   


That must be your opinion.. How long have you been here.. It's not as rare as you say..


It may be my opinion.

 

You can check my profile and see how long I've been here and to which threads I've posted.   You can not tell how many threads I've read as I can not tell how many threads are read by official employees.    For sake of discussion, let's assume I've read 100 threads and in those 100 threads I counted three responses with respondants identified by a name 'ComcastXXXX Official Employee' and a footer also indicating they are an official employee.   I assume they are indeed an employee and responding as an employee.   If I count three threads out of 100 receiving official responses, I'm not going to call it anything but rare.   Even if my thread read count is 1/2 that and only 50 threads, that's a six percent response rate and I would still call it rare.   Maybe they do read 100% of everything posted here but if they respond less than 10% of the time what's the point?    It *appears* as if official Comcast employees are not actively involved with this forum and from a customer perspective, perception is reality.  

<shrug>

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Re: Comcast DNS servers are dropping constantly (75.75.75.75 and 75.75.76.76) ... Revisited 2020

I wasn't talking about employees.... I quoted this comment of yours;

 

"There are, however, a few select individuals that appear to have the ability to escalate a thread to Comcast's attention but it seems that rarely happens."



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Re: Comcast DNS servers are dropping constantly (75.75.75.75 and 75.75.76.76) ... Revisited 2020

Look EG,

 

I'm not trying to knock you.   AFAIK, you are the only person that does escalate threads to Comcast; I won't assume that you are the only person that has this ability, though off the top of my head, I can not recall seeing it done by anyone else.   

 

Perhaps it is the case that threads get escalated and removed from this forum and that's why I do not see them.   I do not read all threads nor do I spend all day on the forum.   I will pop in from time to time, scan things, maybe chime in on a thread if I think I can help someone.   I do not read other topics such as TV, Phone, Apps, etc., I stick to Home Network.  Maybe it is the case that 50% of all posts on say TV get escalated to Comcast employees, I don't know.    I try to form data driven opinions but I'll admit, I do not actually count each and every time a thread is answered by a Comcast employee or a thread is escalated to Comcast employees.    Like everyone else, I do form impressions based on what I see so I will stick by the qualification of rarely.   To be fair, most of the problems posted here are solved without escalation and IMO, that is due in large part to your work.  I will freely admit that I'm wrong about my impressions if there's data to back up that I am wrong and that I had access the same data so I could have formed a better impression.   

 

Back to that particular poster.   Are you telling me that the poster's issue would have been escalated to a Comcast employee based solely on that post, without first having gone through at least checking signal quality and counters?    I will truly be surprised if that is the case. 

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Re: Comcast DNS servers are dropping constantly (75.75.75.75 and 75.75.76.76) ... Revisited 2020


@cxrider wrote:

 Are you telling me that the poster's issue would have been escalated to a Comcast employee based solely on that post, without first having gone through at least checking signal quality and counters?    I will truly be surprised if that is the case. 


I've said, nor inferred nothing of the sort..........



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