Windows 10 and Microsoft Office Weirdness When OpenVPN is Connected
In order to maximize my personal privacy and security and prevent my ISP from interfering with or redirecting my HTTP requests, I usually run all my traffic through a personal OpenVPN setup I have running on a VPS. For the longest time, I was experiencing all sorts of weird issues when OpenVPN was connected on my Windows 10 desktop at home. Microsoft account related-things like downloading apps from the Windows Store wouldn't work, Microsoft Word/Excel/PowerPoint would tell me that I wasn't connected to the internet whenever I attempted to save/sync a file from my OneDrive account, and OneNote would downright crash, which was supper annoying. I always assumed that this was because Microsoft must have blocked my VPN's IP address, although interestingly, I experienced no such issues when connecting to the VPN from my school's network.
It wasn't until I came across this article by Morgan Simonsen that I finally figured out what was going on. My VPS is hosted on a network that doesn't support IPv6 yet, but the local OpenVPN TAP adapter has no way of knowing that (even though IPv6 is enabled by default on network adapters in Windows, it seems).
The obvious solution is to disable IPv6 on the Windows OpenVPN TAP adapter, but if your primary network interface also supports IPv6, you're at risk for IPv6 leaks. You could always disable IPv6 globally, but that's not exactly a 21st-century friendly solution. Your best bet is probably just to find a VPN/VPS provider that natively supports IPv6, at least until OpenVPN implements an option to null-route or blackhole client IPv6 queries on hosts without IPv6 support.