[EDIT] I eventually figured out that it wasn't the 'Google-ness' of the sites that made them magically work, but rather, that IPv6 addresses in general were unaffected by my problem.
This is a very strange one....
About 24 hours ago, my "internet" began malfunctioning. The symptom is that suddenly, most (but not all!) websites will become unreachable and begin timing-out within my browser. This happens on my PC which is wired to my router, and the same symptoms are also seen on any devices attached wirelessly to my network. (tablets, phones, etc.)
But here's the kicker, all Google sites (Gmail, YouTube, Google News) continue to be reachable from all the devices. (Within a browser at least, I haven't tested any apps on those non-PC devices. Nor have I tested any non-web protocols on the PC.)
I believe that the Comcast/Xfinity homepage will also load while I'm in my failed state, but I can't log in or reach sub-pages like the "Support" tab. Obviously, there there be other sites that still work, that I haven't tried, but things like Amazon and Reddit are unreachable.
If I power cycle my modem, or have Comcast "hit" the modem, or I restart the modem via its webpage, the issue goes away for 15-30 minutes, but will eventually return. I have a fan blowing on the modem now, but I don't think it's made a difference in the average time-to-failure.
Any idea what might cause this? The Comcast troubleshooter I spoke to on the phone didn't know what to make of it. I'd "normally" guess that my modem is likely dying, but I can't imagine what sort of hardware issue would leave Google branded sites unaffected.
I am using a privately owned Motorola SB6120. It's about 3 years old at this point.
I am using Google's DNS servers (I think), so perhaps that's a clue.
Please let me know if there's any info I can supply, or procedures I can try, to aid in a diagnosis. I know that swapping in a new modem would be a nice test, but I'd like to avoid that expense if this is just a software or config issue.
Thanks a bunch.
First switch back to Comcast's DNS and see if it works. Sounds like your only working on IPv6 and no connectivity to IPv4.
Interesting! (And thank you for responding so quickly.)
On my modem configuration page I did notice that it says,
"Modem's IP Mode | IPv6 Only"
Does that sound correct? I hope so since I wouldn't know how to change it, unless resetting the modem to its defaults would do so.
Okay, so I need to reset my DNS servers.... Hmm, it's been a while. I guess I need to do this in my router settings, correct? (Since my entire network seems to be having the problem.) I don't know what Comcast's DNS servers are any more. Hopefully that's stickied somewhere here. Or maybe I can tell my router to grab this info automagically?
Oh well, I'll futz around with it. Thanks again.
I switched the DNS server IPs specified in my router's config back to Comcast's. I also switched the DNS settings within Windows back to "acquire automatically". Judging by ipconfig, those changes have all been picked up correctly. I rebooted the PC and the router just to be certain.
This change does not seem to have solved the issue. Upon returning from that reboot, the internet was in flaky mode again, and I needed to reset the modem again. About 45 minutes later, it failed again. Interestingly, I'm still in "failure mode" as I type this. I am able to view this forum right now, even though other (non-Google) sites seem unreachable. This forum is currently very slow however, but perhaps that is normal.
Is there a way to test whether IPv6 sites always work for me, while IPv4 sites sometimes do not? Besides just looking at random sites, I mean? Are there any "test IPs" I can try?
Also, let me know if I should tell my modem to revert to its defaults. I'm not sure what the ramifications are of that, if any. I won't have to do the provisioning step again, will I? The modem's config page says the following on that subject:
"Resetting the cable modem to its factory default configuration will remove all stored parameters learned by the cable modem during prior initializations. The process to get back online from a factory default condition could take from 5 to 30 minutes. Please reference the cable modem User Guide for details on the power up sequence."
Thanks again for any advice.
Bypass the router, connect the ethernet cable directly to the modem and power cycle it. Make sure the network adapter settings are on auto or DHCP.
The modem itself passes through the settings for the DNS from Comcast, none of these are configured by the modem, only the router or pc network settings can modify the DNS. Even try another computer, you might have caught some kind of redirection malware or settings were placed in your hosts file.
Thanks again. Unfortunately, the internet gremlens struck the same week as I threw my back out, so I'm pretty much confined to my chair. It'll be a day or three before I'll be up to re-jiggering my eithernet cables. Your re-wiring suggestion is a good one, as that may serve to eliminate the router as a possible culprit.
While I haven't checked things out on another computer, I am seeing the same issues on my wifi-connected tablet, as well as on my wife's tablet. Given that, I'm leaning towards the hypothesis that the problem exists somewhere upstream of my various clients. That puts the problem in my router, or in my modem, or somewhere in Comcast's network. Since the problem can be temporarily "fixed", without fail, by resetting my modem, that's where my suspicions mainly lie at the moment. But please let me know if you think I'm barking up the wrong tree. My network fu is very weak.
I've hunted up an IPv6/IPv4 test page. I just re-set my modem, so everything looks A-OK right now. I will attempt to re-do the tests once things start failing again. I will also verify that another hard-wired computer I have in another room is experiancing the same issue.
I think I will also do a full factory reset on my modem. If you never hear from me again, it'll be because that was a bad idea!
Okay, the failure just occured again. Here's some results from that test page I referenced above.
From the "Tests Run" tab:
Test with IPv4 DNS record -------- timeout (15.010s)
Test with IPv6 DNS record -------- ok (0.135s) using ipv6
Test with Dual Stack DNS record --------- ok (0.165s) using ipv6
Test for Dual Stack DNS and large packet ------ ok (0.127s) using ipv6
Test IPv4 without DNS ------- timeout (15.010s)
Test IPv6 without DNS --------- ok (0.131s) using ipv6
Test IPv6 large packet ------- ok (0.089s) using ipv6
Test if your ISP's DNS server uses IPv6 -------- ok (0.266s) using ipv6
Find IPv4 Service Provider ------- timeout (15.011s)
Find IPv6 Service Provider ------ ok (0.168s) using ipv6 ASN 7922
From the "For the Help Desk" tab:
Your Internet help desk may ask you for the information below.
Dont go by what the modem says as far as IPv6 only that is only for comcast maintence on the modem and has nothing to do with public IPv4 and Ipv6. It does seem as your Ipv4 is not working are you sure your computer does not have Ipv4 disabled for what ever reason ?
No, I'm not worried about my modem being "permanently trapped in IPv6 mode" or something like that. At least not any more. I read up on that setting and I agree that it's not something to worry about.
I think it's pretty unlikely that my computer is the cause of my "no-IPv4" failures, for two reasons:
I've ordered a new modem. It's supposed to arrive on Saturday. I'll hook it up, get it added to my Comcast account, and see if my problem goes away. If it does, yay! If it doesn't, at least I'll be able to eliminate the modem as a cause. That would just leave my router, or something in Comcast's signal chain as the main suspects. Once my back feels better, I'll be able to take my router out of the chain to see if that's changes anything.
But hopefully, swapping my modem will fix everything.
PS. Does anyone know what the best/fastest way is to get my new modem provisioned is? Should I call Comcast CS, or is there a way to do it "online", self-installl style?
PS. Does anyone know what the best/fastest way is to get my new modem provisioned is? Connect it to the coax cable.
Power it up and wait until the "Online" light is steadily lit. Connect a computer to it with an ethernet cable. Open the computer's browser and you may see their "Walled Garden" modem self registration page. If so, follow the screen prompts. Have your CC account number handy.
If not, call 1-800-comcast and tell a rep that you would like to have a new modem provisioned for service. Have the MAC address and the serial number of the modem handy. These are typically located on a label on the bottom or the back.
Fixed! Hopefully! Knock on wood!
My "new" (refurbed) modem arrived a day early and I got it installed. The web-based self-provisioning process went very smoothly, but I had all kinds of trouble getting my network back up and running. My client devices couldn't "see" my router, etc. I kept swapping-in new ethernet cables, and temporarily bypassed a switch, and eventually it all started working again.
So, yay. It seems like it was indeed my modem that was the problem. Probably. I'll have to see if the fix actually persists for longer than an hour this time.
My back is very angry at me now, but at least I can surf the web while recuperating. Thanks, everybody, for all the advice.