OpenVPN 2.3.2-I003, Windows 7 x86_64 When attempting to establish a IPv6 tunnel on Windows, if you see the following error:

NETSH: C:\Windows\system32\netsh.exe interface ipv6 set address Local Area Connection 2 2402:b300:100:aafc:4000:1234:0:1000 store=active
ERROR: netsh command failed: returned error code 1

then you probably do not have IPv6 enabled on your Windows machine. IPv6 is controlled in the registry via the key HKLM\SYSTEM\CurrentControlSet\services\TCPIP6\Parameters\DisabledComponents, the default value of which is 0x10. To enable IPv6 on all network interfaces, change this value to 0x0. There are several other options for this key; see Microsoft KB 929852 for more info. In my tests, the only value I could get to work with OpenVPN was 0x0, although I also tried Microsoft Fix it 50443, which enables IPv6 on all tunnel interfaces.