IPv6

::/0 # default IPv6 route

# disable IPv6
echo 1 > /proc/sys/net/ipv6/conf/eth0/disable_ipv6
echo 1 > /proc/sys/net/ipv6/conf/all/disable_ipv6
echo "net.ipv6.conf.all.disable_ipv6 = 1" > /etc/sysctl.d/01-disable-ipv6.conf
 
# grub: /etc/default/grub
GRUB_CMDLINE_LINUX_DEFAULT="ipv6.disable=1"
update-grub
 
# sysctl
sudo echo "net.ipv6.conf.all.disable_ipv6 = 1" >> /etc/sysctl.d/01-disable-ipv6.conf
sudo echo "net.ipv6.conf.default.disable_ipv6 = 1" >> /etc/sysctl.d/01-disable-ipv6.conf
sudo echo "net.ipv6.conf.lo.disable_ipv6 = 1" >> /etc/sysctl.d/01-disable-ipv6.conf
sysctl -p /etc/sysctl.d/01-disable-ipv6.conf
 
sudo sed -i 's|udp6|#udp6|g' /etc/netconfig
sudo sed -i 's|tcp6|#tcp6|g' /etc/netconfig

wget -q http://checkipv6.dyndns.com/ -O-

ping 2001:4860:4860::8888 # Google DNS resolver
ping 2606:4700:4700::1111 # Cloudflare DNS resolver