One method to disable IPv6 with Linux Mint is to use the following commands.
sudo nano /etc/sysctl.conf
Add the following lines to the bottom of the file and save it:
# IPv6 disabled
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1
Restart sysclt using the following command:
sudo sysctl -p
If IPv6 is still enabled after rebooting, you create the file /etc/rc.local and and use the following lines:
#!/bin/bash
# /etc/rc.local
/etc/sysctl.d
/etc/init.d/procps restart
exit 0
Use chmod command to make the file executable:
sudo chmod 755 /etc/rc.local
To manually disable IPv6, use the commands below:
sudo sysctl -w net.ipv6.conf.all.disable_ipv6=1
sudo sysctl -w net.ipv6.conf.default.disable_ipv6=1
sudo sysctl -w net.ipv6.conf.lo.disable_ipv6=1
http://itsfoss.com/disable-ipv6-ubuntu-linux