There is a WiFi network that I regularly use, and it seems to be blocking all VPN traffic other than IKEv2. I tested this by downloading many of the free/freemium VPN apps from the Google Play Store on my phone. Only apps that use IKEv2 work, OpenVPN and other protocols fail. One app specifically allows me to choose between OpenVPN TCP, OpenVPN UDP, and IKEv2. Both OpenVPN options are blocked, but IKEv2 works well.
Would it be possible for the router/firewall to be able to differentiate between encrypted IKEv2 and OpenVPN traffic, or is it just relying on port numbers to block/allow connections?
Some additional information:
- The network is already known to perform MITM attacks. For instance, I have a website that I run which has HTTPS traffic encrypted by a Lets Encrypt certificate. When I visit this website via the network, I get a warning that the certificate is not trusted. The certificate details reported by my phone while using the network are different from those reported by my phone when I am not using the network.
- I believe that the reason IKEv2 traffic is not blocked is that the network operators provide an optional VPN for use by devices on the network. I am guessing that said VPN uses IKEv2, and thus all IKEv2 traffic is unblocked (I don't know why all IKEv2 traffic is allowed, though).