> I am wondering why the IPv6 is used in the source. To my 
> understand, the internet is still IP v4 currently. IP v6 
is 
> future, we are not there yet.

A near future. All modern operating systems now support 
IPv6, and most popular Internet servers (webservers, MTA, 
DNS..) are now IPv6-ready.

IPv6 is the future, being ready for IPv6 is a good choice.