Next protocols supported are strictly NPN only. If you want to check ALPN support for a specific connection type you can use the following command: openssl s

Next protocols supported are strictly NPN only. If you want to check ALPN support for a specific connection type you can use the following command: openssl s_client -alpn h2 -connect news.ycombinator.com:443 Near the end of the output you'll see the ALPN protocol or `No ALPN negotiated`. I haven't managed to get a list of server-supported protocols so far, not sure if that's even possible with ALPN. This is with LibreSSL 2.3, but I expect OpenSSL 1.0.2 to support it too.