List current values.
$ sysctl net.ipv6.conf.all.disable_ipv6
net.ipv6.conf.all.disable_ipv6 = 0
$ sysctl net.ipv6.conf.default.disable_ipv6
net.ipv6.conf.default.disable_ipv6 = 0
Or on the wifi net.ipv6.conf.wlp0s20f3.disable_ipv6
interface. List all interfaces with netstat -i
$ sysctl net.ipv6.conf.eth0.disable_ipv6
net.ipv6.conf.eth0.disable_ipv6 = 0
Set 1
to disable.
$ sysctl net.ipv6.conf.all.disable_ipv6=1
$ sysctl net.ipv6.conf.default.disable_ipv6=1
$ sysctl net.ipv6.conf.eth0.disable_ipv6=1
To make it persistent append variable GRUB_CMDLINE_LINUX
in /etc/default/grub
GRUB_CMDLINE_LINUX="ipv6.disable=1"
Update grub
settings with grub2-mkconfig -o /boot/grub2/grub.cfg