Can I use TCP, if I set up OpenVPN UDP connection?

Question

If i established openvpn connection through udp(proto udp), can i use tcp in it(tcp convert to udp somehow), or only udp?

Answer 1

In short: Yes, you can send TCP through an VPN-Tunnel which is transported via UDP. In fact you can tunnel any protocol support by OpenVPN no matter what transport you choose.

Answer 2

You can use any protocol you like, even raw IP. OpenVPN simulates a fully-fledged network device (to some extend – whether it's based on the Ethernet or the IP layer depends on configuration) which behaves like any other network adapter. So you can of course use TCP and UDP in it.

The packages sent via the OpenVPN devices are encrypted and passed through the UDP “connection” used by OpenVPN to the remote side, where they're decrypted and passed on to routing to forward them to their final destination (which might be the remote itself).