HTTPv2 is gaining traction fast and SPDY is set to be deprecated in the coming months.

So a handy command to have in your toolbelt is how to check what protocols a server has enabled.

Be sure to update openssl to gain the -nextprotoneg parameter.

openssl s_client -connect www.amazon.com:443 -nextprotoneg ''  

You should see something like the following for websites that support HTTPv2 (h2)

CONNECTED(00000003)  
Protocols advertised by server: h2, spdy/3.1, http/1.1  
...

or for Amazon in our example I saw:

CONNECTED(00000003)  
Protocols advertised by server: http/1.1  
...

Enjoy !