How to check the SSL protocol version?

Colleagues, how can I check, for example, in the terminal what version of the SSL protocol I have in the OpenWrt router?

The curl tool in verbose mode -v can tell you the TLS version and the chosen cipher suite:

$ curl -Iv
*   Trying 2a03:b0c0:3:d0::1a51:c001:443...
* Connected to (2a03:b0c0:3:d0::1a51:c001) port 443 (#0)
* SSL connection using TLSv1.2 / ECDHE-ECDSA-AES128-GCM-SHA256

The -I option tells curl to fetch HTTP headers only, not the whole page.

Replace with the domain or IP address of the OpenWrt router.