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On windows 7, IPv6 is working by default. On Win 10, this command fixed it (cmd.exe) - netsh interface ipv6 set prefixpolicy fc00::/7 37 1 store=active
Premanently fixed by command : netsh interface ipv6 set prefixpolicy fc00::/7 37 1 store=persistent

On windows 7, IPv6 is working by default. On Win 10, this command fixed it (cmd.exe) - netsh interface ipv6 set prefixpolicy fc00::/7 37 1 store=active
Premanently fixed by command : netsh interface ipv6 set prefixpolicy fc00::/7 37 1 store=persistent

What is the difference between protocols?

UDP is a connectionless protocol, so during the handshake it is not always possible to do an effective error correction. As a result, when there's high ping or low quality line during the OpenVPN login, the handshake may fail, although you could see no significant problem after (if) the connection is established.
TCP is capable of handling these problems.

On the other hand, UDP is more efficient once the connection is established. OpenVPN also implements a basic packets error correction even in UDP (only after the tunnel is established).

If you experience problems with VoIP video/audio conversations when connected to the VPN through a TCP port, a typical case for which a difference may be visible (VoIP over TCP - for example UDP over TCP -  is clearly inferior to VoIP over UDP because TCP implements ARQ, UDP does not), then go for an UDP connection.

In general, you should always try an UDP connection if your ISP allows it and you don't experience any problem during the handshake.
However, TCP is mandatory if you need a proxy to reach the Internet. VPN over TOR connections require a TCP connection.

Variety of ports (53, 80, 443) is an additional option to try to bypass country or ISPs blocks, or bandwidth management. When OpenVPN connections are disrupted by your ISP (this happens for sure in China and Iran) then you need OpenVPN over SSL or OpenVPN over SSH supported by every AirVPN server and requiring, again, TCP.