Optimizing Debian Plesk Server

Today we had a very strange issue on one of our debian based plesk server where sites were loading too slow, After investigation we finally revealed that Debian switches on IPv6 by default, and then uses this before it uses IPv4 for DNS resolution hence causing DNS delays and site loading slow.  So we need to set the ipv6 to off and then reboot the server. Here is how it should be done on the server. Login into the server [...]