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Intermittent DNS/DHCP issues

New Poster

Intermittent DNS/DHCP issues

Intermittent outage that is going to drive me to replace comcast as an internet provider. I randomly stop name resolution. I chatted with an online agent (is this support now gone?). I am an IT pro for over 20 years. He had me check cables, reboot pc, rebooted my gateway, blah blah, blah. I went to a comcast store and replaced  the gateway, still having the issue. Comcast - i need this resolved or next call is to cancel my service. Details below:

 

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New Poster

Re: Intermittent DNS/DHCP issues

and the pictures i uploaded are not showing, awesome

Expert

Re: Intermittent DNS/DHCP issues

Can't see your pics. Since you are a new poster, they likely need to be approved by a Forum Admin. Or you may need to make a minimum number of posts.

You could try hosting them at one of those free third-party pic hosting sites and post the link to them here.



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Frequent Visitor

Re: Intermittent DNS/DHCP issues

@km10982 Your pictures are showing up for me at this point so they should be able to see them now. Also, I've been in IT for over 5 years myself and am running into the exact same issue at seemingly random, but frequent times over the last few weeks. It will be completely fine all day then all of the sudden it will completely lose all WAN connectivity including DNS then come back a minute or a few minute later as of it nothing was wrong. It can happen any time, but it seems to happen primarily, coincidently or not, in the evening between 7PM and 11PM for a few minutes at a time.

I've been using Xfinity service at this address for over 5 years and I never had this problem up until a few weeks ago. I use a Comcast approved SB8200 that was properly activated and provisioned with the correct boot file along with a Netgear Nighthawk R6700v3 using the most current firmware. I had the same problem with a Netgear CM1000 which led me to get the SB8200 in the first place thinking the WAN port was failing. The router is also fairly new as I replaced that originally when it started happening in the first place back in April thinking my router WAN port was going bad. When this happens, none of my status lights on either device change and the modem simply shows a slew of CM-STATUS message sent messages along with periodic ones for MDD Message timeouts. No T3 timeouts occur or appear in the log. but I can say that the OFDM channel 159 using 678000000 Hz drops by a good 7-8 dB to 30 or less, causing a slew of corrupted uncorrectable codewords.

Long story short, you aren't alone and I'm getting fed up with it as well considering I've practically ruled out every device from Layer 1 to Layer 3 I could think of that would be causing it to happen so frequently on my end.

New Poster

Re: Intermittent DNS/DHCP issues

interesting, this sounds like the same problem indeed, but my outage frequency is alot more.

 

Another weird part of this is that if I am on a skype call on my pc i dont drop it. I cant establish any new connections for email refresh, web sites, etc... but the established session to a Skype server persists. When i drop that call and try to get a new one....no luck.

 

I moved DNS to 1.1.1.1 for some of my pc's but still doesnt resolve. But given DHCP issue the problem seems to be local.

 

I'm moving soon and have to choose new providers, comcast included. Seems unlinkely i can go with them.

Official Employee

Re: Intermittent DNS/DHCP issues

Hello all, thanks for reaching out to our Forums! I'm sorry to hear about the intermittent connection you are experiencing. I would be more than happy to further run some diagnostics on my end. Based on the remote troubleshooting that has been done so far, I am wondering if a tech has been out to your location to further investigate these concerns? 


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Contributor

Re: Intermittent DNS/DHCP issues

It seems we're all in the same boat. I also happen to be an IT pro local government here.

I had some line noise issues resolved but now I seem to have DNS issues. My home will lose internet but I can ping DNS servers from pc's on the network and from the gateway (Netgear) itself via diagnostics
Official Employee

Re: Intermittent DNS/DHCP issues

Hello @elie2wins, thanks for reaching out to our Forums! I'm also sorry to hear about the DNS and connection issues you are running into. I'm happy to see you're receiving assistance from another agent in a private message. 


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Frequent Visitor

Re: Intermittent DNS/DHCP issues

@elie2wins I know my issues started around late April, but I also suspect I'm having some ingress issues on a splitter somewhere between my apartment building and the pole. For now, I've switched my Netgear home router to Google public DNS (8.8.8.8 and 8.8.4.4) to see if maybe it's a hand off problem between Xfinity and other networks (I do online game quite a bit and one of the games I play a lot did just recently relocate a data center around the same time my frequent disconnects started). However, I'm also experiencing an issue almost every day where the higher frequencies (639 MHz and up), specifically my OFDM channel (678 MHz), gets a huge influx of ingress from somewhere that trashes my modem speed and incoming frames to the point I have to reboot the modem. It never times out with the CMTS, just completely spams my cable modem with bad frames for anywhere from a few minutes to upwards of a half hour or more.

 

UPDATE: Definitely not DNS related and looks to be completely line/splitter related at this point based on the fact that it has disconnected me pretty much every 15 minutes for the last 3 hours while the damaged frames add up on the OFDM channel. @km10982 If your modem power/SNR levels look normal for the most part and the disconnects you are seeing happen indiscriminately and at any given time for random intervals of time, I would get a tech out there. I suspect you have ingress coming from somewhere that comes and goes like mine.