Weird network problem with CAX80 cable modem

[PatTestsys]

My cable went out 3 days ago after 4 months without issue, and no changes on my side.  The modem showed a problem with too much power on downstream, so Comcast came today and fixed that.  Apparently an upgraded cable line in the neighborhood had more power on the incoming line.  The problem is that while the modem doesn't show any errors, it doesn't work properly.  I can browse certain sites (google, youtube, netgear) but not most others, such as Amazon.  If I can ping the site, I can browse it.  The DNS seems to always resolve, but only the sites that resolve to IP6 addresses actually let the ping go through.  Not sure if that is a coincidence or not.  This happens from multiple laptops, so it is not device specific.  I also cannot ping well known IP addresses like 8.8.8.8, which is the Google DNS.  The built-in Netgear speedtest has a download speed of 600mb+, and upload of 50mb.  Slower than I've gotten (supposed to be 1GB), but still plenty fast.  That always runs.  I've got Comcast scheduled to come back (two more days), but I am suspicious of Netgear CAX80, because no other neighbors are having problems, and I am the only one with a 3rd party modem.  Any ideas would be appreciated.  Never seen anything like this before.

Attaching modem diagnostic logs combined in PDF, after Comcast fix (showing everything OK), and before Comcast fix (showing power problem).  

[PatTestsys · Accepted solution]

I factory reset the modem last night, and after 15 minutes, everything started working.  So something must have gotten corrupted in the modem memory/cache of the modem.  I am back down again, but this time it seems like a normal Comcast outage.  Thanks for the help.

[plemans]

A screen snip is much easier to read (especially for the logs). 

have you tried using your own dns provider? 

Try a different DNS Server. Here's a few for ipv4. Also remember to change the ipv6 dns server if ipv6 is enabled
CloudFlare 1.1.1.1 and 1.0.0.1
GoogleDNS 8.8.8.8 and 8.8.4.4

[PatTestsys]

Yes.  In fact, the (win10) laptop connected to the router was configured for Google DNS (8.8.8.8).  The first thing I tried was to switch it back to the Comcast DNS.  The monitoring software on the laptop (a small app that continuously pings to see if the Internet is connected, and tracks outages) that was failing on the pings to Google (8.8.8.8), Cloudflare (1.1.1.1), and level 3 (4.2.2.2).  

I later tried from my primary laptop (win11), and found the same behavior on both.  The really weird part is how some IP6 addresses are working.  I would think Comcast, but how are the neighbors all working?  I'm going to ask Comcast to try one of their modems;  perhaps the CAX80 is no longer supported.

[plemans]

and you changed the ipv6 dns address as well? 

[PatTestsys]

I switched it from manual (the Google DNS) to automatic, meaning that it got the addresses from the modem, and that got the addresses from Comcast.

I verified that the Netgear modem was set to pass through DNS.  I did not try and set it there.  Pretty sure it only allows you to set iP4 addresses in that UI.

So, no, I didn't do anything else to remove or add IP6 addresses.

In addition to the two laptops, I tried an ipad and iphone.  Just browsing, not pings, but saw similar results (Google worked, Amazon and others failed).  

[plemans]

The screensnip of the logs might help. 

Also, can you disable ipv6? 

[PatTestsys]

By disable ip6, do you mean on a single device?  I can try that when I get home.  Easy to do on my laptops.  Not sure how to do that at the router level.  My expectation is that everything fails, but it will be interesting to see if Google keeps working.  

I am attaching an image of the event log portion of the diagnostic.  The diagnostics are multiple pages, but this is really the only part that wrapped.   

[PatTestsys]

The more I think about this, the more I think this is related to routing problems.  

I cannot ping 8.8.8.8 or 1.1.1.1.  Yet, www.google.com not only can be pinged, but can be browsed (as long as I stay on google).  That's not a DNS problem.  I think there are three possibilities, listing in order of probability: (a) comcast has some sort of router problems at their central office;  (b) cable modem somehow corrupted or fried;  or (c) cable modem has become incompatible with Comcast. 

I would assume (a) except no-one else in the neighborhood is having the same problem.  I have found several neighbors that are complaining that their service is up and down over the last 3 days.  But some say it always works.

(b) could be investigated by resetting the cable modem, and reconfiguring it.  I havent done that yet because I didnt want to introduce another variable.  

(c) seems unbelievable, but who know what Comcast would do to increase revenues.

[plemans]

Your logs are indicating quite a few line issues. 

Start with removing any amplifiers, signal attenuators, or splitters from the coax.
From there check the line for kinks, damage, moisture in the line.
Check the connectors for improperly made ends, foil touching the copper coax line, bad/old/cheap connectors, or corroded connections. Replace them if you do.
If you can, simply connect the modem right where the coax comes into the home. This prevents wiring in the home from being the issue. And some ISP’s charge if the wiring issue is in the home. So this helps prevent this.

[PatTestsys · Accepted solution]

I factory reset the modem last night, and after 15 minutes, everything started working.  So something must have gotten corrupted in the modem memory/cache of the modem.  I am back down again, but this time it seems like a normal Comcast outage.  Thanks for the help.