Sometimes IPv6 networking goes haywire, on a PC, server, or even a whole network. Machines are there, ping may happen or not, but one, some, or all of them just insist on using oddball IPv6 IPs to connect to each other, even though nothing has been changed voluntarily. Given that even after all these years there still are no useful IPv6 blacklists on the Internet, and given the excellent methods in place to use IPv4, we see no need for IPv6 at this time.

But Microsoft does insist on using IPv6 inside its operating systems, so we must keep it running; disabling v6 does harm in a Microsoft environment. The following is Microsoft’s recommendation to instruct Windows to prefer IPv4, which does eliminate the above issue. One adds a DWORD here:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip6\Parameters\

named DisabledComponents. Hex value 20, binary 32. Then reboot.

A quick way to do the registry add, in administrative CMD:

REG ADD HKLM\SYSTEM\CurrentControlSet\Services\Tcpip6\Parameters /v DisabledComponents /t REG_DWORD  /d 32

Still you’ll need to reboot to get it to take effect.

The info is from this reference.