I recently bumped into an annoying problem when trying to establish a VPN connection to a remote site: apparently not only are 20% of all websites blocked in the UK, some ISPs block VPN connections too. Even many of the VPN providers’ websites have been made inaccessible. Luckily I figured out a simple solution to the problem.
As I investigated the problem a bit further, I noticed that the block had been implemented by simply disabling the ports for VPN. In this case the problem was ridiculously easy to solve.
The solution is to replace the default port, 1194 (UDP) in the case of OpenVPN, with a TCP port like 443, so that the packets would look like regular HTTPS traffic.
If you have the same problem and are running your own OpenVPN server, just modify the server config to have the following lines:
proto tcp port 443
If you are using a commercial VPN, though, you will have to check whether they provide an alternative port for OpenVPN. Many of the bigger VPN providers usually do.