There is a way for completely disabling of IPv6.
- type this command for disabling IPv6 in kernel: “sysctl -w net/ipv6/conf/all/disable_ipv6=1”
- for permanent disabling of IPv6 you have to add this line to the “/etc/sysctl.conf” “net.ipv6.conf.all.disable_ipv6=1”
There is a link for original post (unfortunately in Czech) from official Turris team