50% of Websites Often Won't Load, Bizarre Workaround - Windows 10

Question

my dears. Thanks one and all for any suggestions.

How would you like to start every day spending 10 minutes to 2 hours trying to get your internet to work? Fun stuff, I'm tellin' ya!

I have a cable internet connection (cable to modem, modem has 4 ethernet ports - I use one ethernet cable to my comp, another to a wifi router).

Almost every time I put my computer to sleep, or restart, I have connectivity issues. I'm using the Google DNS servers and all Google sites, YT etc. load perfectly fine. But many other websites (including Stack Overflow and countless others) time out and won't load. Twitter, for instance, starts to load the menus and everything else except for the feed.

I've re-installed Windows 10. I've run the gamut of command prompts (flushdns, ipconfig renew & release, etc.). When I'm struggling with connectivity, the command prompt tells me that the media is disconnected. I've tried a factory reset on the modem. The whole shebang.

The only workaround is to swap ethernet jacks (one out to my comp, another out to my wifi router) over and over, until finally some combo works. 4 jacks, 2 cables - I keep swapping and swapping and swapping them in different combinations until finally the problem resolves. There is no consistency, I have to play this game literally every time my computer restarts or emerges from sleep.

Another workaround that (sometimes) works is to connect to my wifi on my iPhone, use it as a hotspot, and connect the computer via bluetooth. So comp > wifi > iPhone > comp in a loop.

Does anyone have any clue what on God's green Earth could be causing this? I don't mind occasionally tearing a lock or two of hair out, but I'm going bald here!

Answer 1

The most common cause of "Google properties work but most other sites don't" is when Path MTU Discovery isn't working and your MTU (1500 by default) is too high for your main path to the Internet.

A common workaround is to manually set the MTU—on the NIC on the device in question—to a lower value like 1300, then see if that solves the problem, and then keep adjusting it higher and retesting until you find the highest value that works.

If lowering your MTU below 1500 solves the problem, it confirms that you have a Path MTU Discovery problem on your network. You can leave the "manually lowered MTU" workaround in place, but the real solution is to discover which router is failing to send or forward the ICMP "Destination Unreachable: Fragmentation required but 'Don't Fragment' bit set" messages that the Path MTU Discovery algorithm relies upon.

Answer 2

There are a couple of things o check/verify/try...

First of all Google and related sites are fine but everything else is acting up.
That excludes a flaky network interface or dodgy LAN cables. In that case everything would go bad.
But it suggests there is a DNS issue, DHCP issue or maybe an ip-address conflict, possibly be caused by having 2 active routers (your cable-modem is most likely a router and you have that 2nd router used as access-point).

You mention that you use Google DNS, but have you configured that in the cable modem (which usually is also a router) or just on your PC?
Try configuring it on BOTH.
Also see, just to test, what happens if you switch to CloudFlare DNS (1.1.1.1) of Cloud9 (9.9.9.9) or just use your ISP default settings. (Some ISP's really mess with the DNS and only work properly if you use their own DNS settings.)

How is the 2nd router (used as access-point) connected to the cable-modem?
If you have one of the LAN ports of the 2nd router connected to the cable-modem you have to DISABLE DHCP on the 2nd router. If you don't that will be the cause of all sort of weirdness. (And you will have to set the LAN ip-address of the 2nd router to an unused ip-address in the range used by the cable-modem.)
If you have the 2nd router connected by its WAN interface to the cable-modem that won't cause any issues, if at least you make sure the LAN side of the 2nd router uses a different ip-range from the ip-range that the cable-modem is handing out on DHCP.

Last, but not least: If your provider provides ipv4 AND ipv6 make sure you configure DNS servers for BOTH IP protocols. It won't work properly with only ipv4 DNS settings. It also gets weird if you changed the ipv4 DNS to Google but the ipv6 is still on the ISP DNS settings. If you have ipv4 AND ipv6 it may be an option to disable ipv6 altogether (if only just for testing) to see if that makes a difference.