TLS 1.3 not offered and downgraded to a weaker protocol

[Kaushal Shriyan]

Hi,

I am running nginx version: nginx/1.16.1 on CentOS Linux release 7.7.1908
(Core). I have configured *ssl_protocols TLSv1.2 TLSv1.3*; in
/etc/nginx/nginx.conf.
#nginx -t
nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful

Now when I am running testssl.sh (https://testssl.sh/) which is a Testing
TLS/SSL encryption tool, I see the below output

 Testing protocols via sockets except NPN+ALPN
>  SSLv2      not offered (OK)
>  SSLv3      not offered (OK)
>  TLS 1      not offered
>  TLS 1.1    not offered
>  TLS 1.2    offered (OK)
>  TLS 1.3    not offered and downgraded to a weaker protocol
>  NPN/SPDY   h2, http/1.1 (advertised)
>  ALPN/HTTP2 h2, http/1.1 (offered)


Any clue regarding  "TLS 1.3    not offered and downgraded to a weaker
protocol" ? Please let me know if you need any additional information.
Thanks in advance and I look forward to hearing from you.

Best Regards,

Kaushal
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