tl;dr If your VPN isn't working and your computer has an Intel Killer series wi-fi adapter, try disabling the Killer software add-ons (https://wallpunch.net/windows-killer-troubleshooting/)

Occasionally I receive a support request from a user where Wallpunch is working great on their phone, but their Windows PC cannot connect at all. Standard troubleshooting steps yield no clues:

- The Windows app is able to complete the pre-connection authentication step with our servers

- The Windows app doesn't work on different Wi-Fi networks, or when connected to the phone hotspot

- The phone app works fine when connected to the same network as the Windows PC

- The network configuration shown by the "ipconfig" and "route" commands looks normal

- Wallpunch debug logging shows that the PC's traffic is being captured by the VPN tunnel correctly

Everything appears to be functioning completely as expected - except the critical VPN tunnel connections to our servers fail to connect (client records a TCP connection timeout, servers never see any handshake packets).

The first couple times, after exhausting all the debugging options I could think of, I had no choice but to apologize to the user, refund their subscription, and move on. But eventually I noticed a pattern: all of the affected computers had an Intel Killer wi-fi adapter!

Some searching revealed this has been a known problem for a while, with several threads discussing the issue on Reddit as well as the Intel and Microsoft support forums.

- https://www.reddit.com/r/meraki/comments/8638kv/client_vpn_with_killer_network_service/

- https://community.intel.com/t5/Wireless/Smart-AP-disabled-due-to-VPN-Killer-Intelligence-Center/td-p/1513415/page/4

- https://learn.microsoft.com/en-us/answers/questions/4173090/killer-intelligence-centre-causing-a-problem

Nord even has a page on it in their troubleshooting docs: https://support.nordvpn.com/hc/en-us/articles/20226287150609-Intel-Killer-Wi-Fi-adapter-not-working-with-NordVPN

Basically the Killer adapters come with a bunch of software add-ons that are intended to speed up your internet connection but can end up causing problems with VPNs. So far disabling these add-ons has solved the issue for all of my affected users. For detailed steps on how to do so you can check out the threads linked above or this summary page I made: https://wallpunch.net/windows-killer-troubleshooting/

I'm happy to have fixed things for my users but I'd love to get to the bottom of this and figure out how exactly the Killer is blocking VPN connections and if there is a way to get around that blocking without requiring manual user actions. If you know of any good sources of additional information, or if you have an Intel Killer card and would be interested in helping me with further testing, please let me know!