WSAEPFNOSUPPORT 0x0000273E fix: protocol family not configured

Quick answer: Run netsh winsock reset and netsh int ip reset in an admin Command Prompt, then reboot. That fixes 80% of cases.

You're seeing WSAEPFNOSUPPORT (0x0000273E) because Windows' Winsock layer can't match the socket you're trying to open with an available protocol family. That family could be IPv4, IPv6, or something more specific like AF_UNIX or AF_IPX. Most of the time this happens after you've fiddled with network adapter properties—maybe you unchecked IPv6 in the adapter settings, or installed a VPN client that yanked out protocol bindings. I've also seen it after malware cleaners or registry cleaners strip out Winsock catalog entries they thought were junk.

The error shows up in all sorts of apps: web browsers can't resolve DNS, game launchers fail to connect, VPN clients throw this and then quit. The real fix is rebuilding the Winsock catalog and making sure the protocol families are registered correctly.

Step-by-step fix: Reset the network stack

1. Open Command Prompt as administrator. Click Start, type cmd, right-click Command Prompt, and select "Run as administrator." If you skip this, the commands below will fail with an access denied error.
2. Reset Winsock. Type this and press Enter:
   

   netsh winsock reset

   After you press Enter, you'll see: "The Winsock catalog was reset successfully. You must restart the computer in order to complete the reset." Don't restart yet.

3. Reset the TCP/IP stack. Type this and press Enter:
   

   netsh int ip reset

   You'll see a lot of text fly by. Wait for it to finish. It'll say something like "Resetting Global, OK!" and then prompt you to restart.

4. Flush DNS and reset other networking bits. Run these three commands one at a time, pressing Enter after each:
   

   ipconfig /release
   ipconfig /renew
   ipconfig /flushdns

   /release drops your current IP lease. /renew gets a new one. /flushdns clears the DNS cache. If /renew times out, don't panic—just move to the next step.

5. Reboot your computer. This step is mandatory. The Winsock reset doesn't take effect until Windows restarts.

If the error persists: Check protocol bindings

1. Open Network Connections. Press Win + R, type ncpa.cpl, and press Enter.
2. Open your active adapter's properties. Right-click your Ethernet or Wi-Fi adapter and select "Properties."
3. Check that both IPv4 and IPv6 are checked. In the list, look for "Internet Protocol Version 4 (TCP/IPv4)" and "Internet Protocol Version 6 (TCP/IPv6)." If either one is unchecked, check it. Click OK.
4. Install missing protocols manually. If the protocol entries are gone entirely (not just unchecked), click the "Install..." button, select "Protocol," click "Add," and choose "Reliable Multicast Protocol" or "Microsoft IPv6 Protocol" from the list. This re-registers the protocol family in Winsock.
5. Reboot again.

Alternative fix: Registry repair for corrupted Winsock catalog

If the netsh commands run without errors but the problem comes back after reboot, the Winsock catalog in the registry might be corrupted. This is rare, but it happens after some VPN installers or security suites mess with the registry.

1. Open Registry Editor. Press Win + R, type regedit, press Enter. Say Yes to the UAC prompt.
2. Go to the Winsock keys. Navigate to:
   

   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\WinSock2\Parameters

   Look for two entries: Protocol_Catalog9 and Namespaces_Catalog5. Right-click the whole Parameters folder and select "Export" to back it up first.

3. Delete the catalog subkeys. Right-click Protocol_Catalog9 and delete it. Do the same for Namespaces_Catalog5. I know this sounds scary, but Windows rebuilds these on the next boot.
4. Reboot. Windows will recreate the Winsock catalog from scratch using the default system files.
5. Reset Winsock again. After reboot, run netsh winsock reset again (in admin CMD) and reboot one more time.

Prevention tip: Stop software from stripping protocol bindings

The number one cause of WSAEPFNOSUPPORT is VPN clients that disable IPv6 or remove protocol bindings during install or uninstall. I've seen NordVPN, ExpressVPN, and OpenVPN GUI do this. Before you install a VPN, create a System Restore point. After installing, check your adapter properties—if IPv6 is unchecked, recheck it. If your VPN client keeps unchecking it, switch to a different VPN provider that handles protocols properly.

Also, stop using so-called "registry cleaners" and "PC optimizers." They often strip Winsock entries they mistake for orphaned data. Windows manages its own network stack just fine without third-party tools.

When all else fails: Network reset in Windows 10/11

Windows 10 version 1607 and later, plus all Windows 11 versions, include a built-in network reset that does everything above plus removes all network adapters and drivers. Here's how:

1. Open Settings (Win + I).
2. Go to Network & Internet > Status.
3. Scroll down to Network reset and click it.
4. Click Reset now. Read the warning—you'll lose saved Wi-Fi passwords and VPN connections. Write them down first.
5. Your PC will restart automatically. After it boots, reconfigure your network.

This nukes the problem completely. I only recommend it if the earlier steps failed, because it's a pain to re-enter all your Wi-Fi credentials.