CentOS 8.x Disabling IPv6

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Disable IPv6 using sysctl

1. First check whether IPv6 is enabled or not using:

   ip addr | grep inet6

2. Create /etc/sysctl.d/70-ipv6.conf with following contents:

   net.ipv6.conf.all.disable_ipv6 = 1
   net.ipv6.conf.default.disable_ipv6 = 1

3. Now to disable IPv6 use:

   sysctl --load /etc/sysctl.d/70-ipv6.conf

Note that due to use of network manager IPv6 might get enabled on reboot. For that we can try to disable IPv6 for interface using nmcli using:

   nmcli connection
   nmcli connection modify <connection> ipv6.method ignore

after replacing <connection> with appropriate connection name

Refer:

• https://www.tecmint.com/disable-ipv6-in-centos-8/

Disable IPv6 using kernel boot options

To disable IPv6 using kernel options use:

1. Edit /etc/default/grub and append option:

   ipv6.disable=1

   in GRUB_CMDLINE_LINUX using:

   GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX ipv6.disable=1"

2. Create updated grub configuration using:

   grub2-mkconfig -o /boot/grub2/grub.cfg

3. Reboot system and validate

   shutdown -r now

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