How to Disable IPV6 on RHEL 8 / Rocky Linux 8 / Alma Linux 8

Method 1: Using GRUB2

Edit /etc/default/grub and append ipv6.disable=1 to GRUB_CMDLINE_LINUX 

GRUB_CMDLINE_LINUX="rd.lvm.lv=rhel/swap crashkernel=auto rd.lvm.lv=rhel/root ipv6.disable=1"

Run the grub2-mkconfig command to regenerate the grub.cfg file:

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

Alternatively, on UEFI systems, run the following:

grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg

Reboot Server

reboot

 

Method 2: Using sysctl

Create File ipv6.conf

nano /etc/sysctl.d/ipv6.conf

==============================

# First, disable for all interfaces
net.ipv6.conf.all.disable_ipv6 = 1

# If using the sysctl method, the protocol must be disabled all specific interfaces as well.
net.ipv6.conf..disable_ipv6 = 1

==============================

Reloaded

sysctl -p /etc/sysctl.d/ipv6.conf

Create a backup of the initramfs before making any changes to it:

cp /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r).bak.$(date +%m-%d-%H%M%S).img

rebuild the Initial RAM Disk Image

dracut -f -v

Comment out any IPv6 addresses found in /etc/hosts, including ::1 localhost address. Make backup of the file before making any changes:

cp -p /etc/hosts /etc/hosts.disableipv6

sed -i 's/^[[:space:]]*::/#::/' /etc/hosts

VERIFICATION

1. The current state of the ipv6 module disable option can be seen via sysfs:

# cat /sys/module/ipv6/parameters/disable
1

2. The current state of the sysctl disable_ipv6 can be seen with the sysctl command:

# sysctl -a 2>/dev/null | grep disable_ipv6

net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 0
net.ipv6.conf.eth0.disable_ipv6 = 0

3. To list any IPv6 addresses assigned to the system:
 

ip -6 addr

4. To list any IPv6 TCP or UDP sockets something like the following can be used:
 

ss -6 -pan