DTLS 1.0, which is insecure and should not be used
DTLS 1.2, defined by RFC 6347
SSL 3.0, which is insecure and should not be used
TLS 1.0, which is insecure and should not be used
TLS 1.1, which is insecure and should not be used
TLS 1.2, defined by RFC 5246
TLS 1.3, defined by RFC 8446
No protocol version or unknown protocol version
The TLS or DTLS protocol version used by a #GTlsConnection or #GDtlsConnection. The integer values of these versions are sequential to ensure newer known protocol versions compare greater than older known versions. Any known DTLS protocol version will compare greater than any SSL or TLS protocol version. The protocol version may be %G_TLS_PROTOCOL_VERSION_UNKNOWN if the TLS backend supports a newer protocol version that GLib does not yet know about. This means that it's possible for an unknown DTLS protocol version to compare less than the TLS protocol versions.