FAQ — CC

Answers to common problems reported to the Computer Centre.

VPN certificate errors

OpenVPN fails to connect with a TLS “unsupported protocol” error.

The error looks like this:

TLS error: Unsupported protocol. This typically indicates that client and server have no common TLS version enabled.
OpenSSL: error:1425F102:SSL routines:ssl_choose_client_version:unsupported protocol

Why it happens: the client and server have no TLS version in common. This can be caused by mismatched tls-version-min and tls-version-max options. If your OpenVPN client is between v2.3.2 and v2.3.6, it uses TLS 1.0 only.

Fix: add tls-version-min 1.0 to the client configuration, or start OpenVPN with that option (replace the file name with your own .ovpn file):

sudo openvpn --config your_ssl_vpn_config.ovpn --tls-version-min 1.0 --auth-nocache

See HBCSE VPN details for the full VPN setup.