rd is TLSv1.3 which was released in 2018 as RFC8446.</p>

<p>Today TLSv1.3 and TLSv1.2 are the most commonly deployed versions of the protocol. The IETF have formally deprecated TLSv1.1 and TLSv1.0, so anything below TLSv1.2 should be avoided since the older protocol versions are susceptible to security problems.</p>

<p>OpenSSL does not support SSLv2 (it was removed in OpenSSL 1.1.0). Support for SSLv3 is available as a compile time option - but it is not built by default. Support for TLSv1.0, TLSv1.1, TLS