Disable IPV6

Proven method for disabling IPV6 on your Linux machine.

Why even disable ipv6?

Sometimes internet things slow down with ipv6. I’ve experienced this many times, and I’ve noticed a marked speed improvement after disabling this. I once got down and dirty in the internals of some log somewhere and noticed that all my DNS queries were being tried first at ipv6, then after failing they would be tried as ipv4, every single time. Ideally ipv6 would just work well, but sometimes that is not the case.

If you’re curious whether or not your system has ipv6 enabled, run this in a terminal to check:

ip -6 addr show

If so, you’ll see something like this:

🪶Aegix:[beach✨byzantium ~]$ ip -6 addr show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 state UNKNOWN qlen 1000
    inet6 ::1/128 scope host proto kernel_lo
       valid_lft forever preferred_lft forever
3: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
    inet6 fe80::f18a:5a15:eec4:3b94/64 scope link noprefixroute
       valid_lft forever preferred_lft forever

How to disable ipv6

  • Edit /etc/default/grub
sudo vim /etc/default/grub

to include ipv6.disable=1.

  • Update GRUB
sudo grub-mkconfig -o /boot/grub/grub.cfg

Example output:

❯ sudo grub-mkconfig -o /boot/grub/grub.cfg

Generating grub configuration file ...
Found linux image: /boot/vmlinuz-linux
Found initrd image: /boot/initramfs-linux.img
Found fallback initrd image(s) in /boot:  initramfs-linux-fallback.img
Warning: os-prober will not be executed to detect other bootable partitions.
Systems on them will not be added to the GRUB boot configuration.
Check GRUB_DISABLE_OS_PROBER documentation entry.
Adding boot menu entry for UEFI Firmware Settings ...
  • Go crazy

If we wanted to go crazy, we could blacklist the IPV6 kernel module like this:

echo "blacklist ipv6" | sudo tee /etc/modprobe.d/ipv6.conf

Then reboot

Validate your changes took effect

Post-reboot validation:

❯ cat /proc/cmdline
BOOT_IMAGE=/vmlinuz-linux root=UUID=<uuid-value> rw rootflags=subvol=@ loglevel=3 cryptdevice=UUID=<uuid-value>:aegixluks root=/dev/mapper/aegixluks ipv6.disable=1
❯ ip -6 addr show
❯ lsmod |grep ipv6
❯ ss -tulwn6
Netid    State    Recv-Q    Send-Q       Local Address:Port       Peer Address:Port   Process

The last three commands should return nothing as shown above.

Last modified May 30, 2024: 05/30/24 19:47:20 (155469e)