IPv6 is one of the biggest developments in computer networking. It provided a larger address space for the Internet along with improvements in routing and global addressability. That said, IPv6 adoption is still in its infancy and running IPv6-capable computers on IPv4-only networks can result in connection issues. This article will show you how you can disable IPv6 on your Linux machine and use it in an IPv4-only network.
How to Verify IPv6 Status
The quickest way to check for your machine’s IPv6 status is by running the ip addr command on a terminal. This is a utility that will print all the available network interfaces that are running the IPv6 network stack:
ip -6 addr
You can also check your computer’s kernel binary if it’s running the kernel module for IPv6. The following command will print the “/proc” file path for the IPv6 module if the kernel is actively loading it:
ls /proc/net/if_inet6
How to Disable IPv6 in Linux
For the most part, permanently disabling the IPv6 protocol on Linux will require you to add a new argument to your bootloader. To do this, open your GRUB configuration file with your favorite text editor:
sudo nano /etc/default/grub
Press Ctrl + W, then search for “GRUB_CMDLINE_LINUX_DEFAULT.”
Write ipv6.disable=1 to the end of the variable’s value.
Save (Ctrl + O) and exit (Ctrl + X) the text editor.
Reload your bootloader’s configuration file:
sudo grub-mkconfig -o /boot/grub/grub.cfg
Reboot your system, then run ls /proc/net/if_inet6 to check if you’ve successfully disable IPv6 on your machine.
Good to know: learn how bootloaders work by looking at a comparison between Grub and Systemd-boot.
Disable IPv6 on Red Hat-based Systems
Aside from directly configuring your computer’s bootloader, you can also disable IPv6 on the userland level. This is helpful if you only want to disable IPv6 on certain network interfaces.
To disable IPv6 on Red Hat-based distros, open a new terminal session then list all the available network interfaces for your machine:
ip -6 addr
Find the network interface that you want to disable the IPv6 stack on. In my case, I want to disable it on my “enp1s0” Ethernet interface.
Create a new config file for your IPv6 stack under “/etc/sysctl.d.”
sudo nano /etc/sysctl.d/40-ipv6.conf
Paste the following lines of code inside your new config file:
net.ipv6.conf.all.disable_ipv6 = 1 net.ipv6.conf.YOUR-INTERFACE-NAME.disable_ipv6 = 1
Save your new config file, then run the following commands to reload your new settings:
sudo sysctl -p /etc/sysctl.d/ipv6.conf sudo systemctl restart systemd-sysctl.service
Go inside your machine’s hosts file, then add a pound (#) sign at the start of every line that contains an IPv6 address.
Create a backup of your machine’s original initramfs, then recreate it without IPv6 support:
sudo cp /boot/initramfs-$(uname -r).img /initramfs-backup.img sudo dracut -f
Run the nmcli command and disable its IPv6 method for your interface. This ensures that your settings will persist across system reboots.
sudo nmcli connection modify YOUR-INTERFACE-NAME ipv6.method "disabled"
Lastly, reboot your system to apply your new settings.
FYI: learn more about how computers communicate over the network by looking at some simple and easy uses for Netcat.
Disable IPv6 on Debian-based Systems
Just like in Red Hat-based distros, you can also disable the IPv6 protocol from the userland of Debian-based systems. To do this, open a new terminal then run ip -6 addr to find the name of the interface that you want to disable IPv6 on:
Run the following commands to disable the IPv6 stack on a specific interface:
sudo sysctl -w net.ipv6.conf.all.disable_ipv6=1 sudo sysctl -w net.ipv6.conf.YOUR-INTERFACE-NAME.disable_ipv6=1
Apply the new settings by reloading your sysctl daemon and its Systemd service:
sudo sysctl -p sudo systemctl restart systemd-sysctl.service
Disable the IPv6 method to ensure that Systemd will not overwrite your custom setting:
sudo nmcli connection modify YOUR-CONNECTION-NAME ipv6.method "disabled"
Note: You can find the name of your network interface in nmcli by running nmcli connnection show.
Check whether your network interface still has an IPv6 address by running ip addr.
Tip: if you are a Windows user, here is how you can disable IPv6 in Windows.
How to Re-enable IPv6 in Linux
To re-enable IPv6 in Linux, open your bootloader config file with your favorite text editor:
sudo nano /etc/default/grub
Press Ctrl + W, then search for “GRUB_CMDLINE_LINUX_DEFAULT.”
Remove the ipv6.disable=1 value at the end of the variable.
Save your config file, then reload your bootloader’s settings:
sudo grub-mkconfig -o /boot/grub/grub.cfg
Reboot your system, then check if the IPv6 stack is back up and running.
Re-Enable IPv6 on Red Hat-based Systems
On Red Hat-based distros, you can re-enable IPv6 by editing the sysctl config file. To do this, open a new terminal session, then delete the “40-ipv6.conf” file under “/etc/sysctl.d/.”
sudo rm /etc/sysctl.d/40-ipv6.conf
Reload your sysctl daemon along with its Systemd service:
sudo sysctl -p sudo systemctl restart systemd-sysctl.service
Open your “/etc/hosts” file, then remove the pound (#) sign in front of all the lines that contain an IPv6 address.
Restore the machine’s original initramfs back to its “/boot” partition:
sudo cp /initramfs-backup.img /boot/initramfs-$(uname -r).img sudo dracut -f
Re-enable the IPv6 method on nmcli to ensure that Systemd will load the IPv6 stack on your network interface:
sudo nmcli connection modify YOUR-INTERFACE-NAME ipv6.method "auto"
Reboot your system to apply your new settings, then run ip -6 addr to confirm that the IPv6 stack is up and running.
Re-Enable IPv6 on Debian-based Systems
To restore the IPv6 stack on Debian-based distros, open a new terminal then run the following commands:
sudo sysctl -w net.ipv6.conf.all.disable_ipv6=0 sudo sysctl -w net.ipv6.conf.default.disable_ipv6=0
Reload the sysctl daemon, as well as its Systemd service:
sudo sysctl -p sudo systemctl restart systemd-sysctl.service
Enable the IPv6 stack for your network interface using nmcli:
sudo nmcli connection modify YOUR-CONNECTION-NAME ipv6.method "auto"
Lastly, confirm that your IPv6 stack is working properly by running ip -6 addr and checking if your interface has an IPv6 address.
Learning how to disable and re-enable the IPv6 stack in Linux is just the first step in getting into computer networking. Explore more of this deep and wonderful world by learning how to track packets in your network using Traceroute.
Image credit: Leon Seibert via Unsplash and Wikimedia Commons. All alterations and screenshots by Ramces Red.
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