I'm confused with the technologies that OpenVPN uses. The official site mentions it uses SSL/TLS in-place of IKEv1/IKEv2, and uses IPSec ESP to secure the data, and yet that it isn't compatible with IPSec.
OpenVPN's security model is based on using SSL/TLS for session authentication and the IPSec ESP protocol for secure tunnel transport over UDP. OpenVPN supports the X509 PKI (public key infrastructure) for session authentication, the TLS protocol for key exchange, the OpenSSL cipher-independent EVP interface for encrypting tunnel data, and the HMAC-SHA1 algorithm for authenticating tunnel data.
Use all of the encryption, authentication, and certification features of the OpenSSL library to protect your private network traffic as it transits the internet
OpenVPN is not compatible with IPSec, IKE, PPTP, or L2TP.
Also wikipedia info:
It uses a custom security protocol that utilizes SSL/TLS for key exchange
OpenVPN uses the OpenSSL library to provide encryption of both the data and control channels