Our network fully supports IPv6. But our VPS templates are configured with IPv6 disabled by default. The reason was that when IPv6 is enabled, the operating system will default to IPv6, but many hosts (including software downloads and gaming etc) though having IPv6 configured, does not work very well. Some hosts have IPv6 DNS addresses but the actual address is not optimally announced through IPv6 BGP, causing timeouts before falling back to IPv4. This causes long delays especially tasks like software download and installation.
But your application may be different and could benefit from IPv6. To enable IPv6 manually,
1. Edit the interface config file in /etc/sysconfig/network-scripts/ and add these two lines at the bottom
2. Edit /etc/sysctl.conf and remove all lines with "disable_ipv6 = 1"
Ubuntu / Debian
1. Edit /etc/default/grub and remove all "ipv6.disable=1"
2. Run "update-grub"
3. Edit /etc/sysctl.conf and remove all lines with "disable_ipv6 = 1"
1. Control Panel -> Network and Internet -> Network Connections
2. Right click the network adaptor, choose "Properties"
3. Tick "Internet Protocol Version 6 (TCP/IPv6)"
4. Click "OK"