This configuration parameter specifies Secure Sockets Layer (SSL) and Transport Layer Security (TLS) versions that the server supports for incoming connection requests.
If you set the parameter to null or TLSv1, the parameter enables support for TLS version 1.0 (RFC2246) and TLS version 1.1 (RFC4346).
If you set the parameter to TLSv12 (RFC5246), the parameter enables support for TLS version 1.2. This setting is required to comply with NIST SP 800-131A.
If you set the parameter to TLSv12 and TLSv1, the parameter enables support for TLS version 1.2 with the option to fall back on TLS version 1.0 and 1.1.