Disable IPv6 using Network Manager

Issue

Many VPNs or network connections support only IPv4. That means all IPv6 traffic bypasses the VPN and renders it virtually useless. To avoid this, we can tell Network Manager to avoid IPv6 on an specific network connection.

Fix

We fix this by disabling the IPv6 protocol on a system that uses NetworkManager to manage network interfaces. If we disable IPv6, Network Manager automatically sets the corresponding sysctl values in the Kernel.

Disable IPv6 on a connection using nmcli

Let’s display the list of network connections:

$ nmcli connection show
NAME    UUID                                  TYPE      DEVICE
Example 7a7e0151-9c18-4e6f-89ee-65bb2d64d365  ethernet  enp1s0

Now we are going to set the ipv6.method parameter of the connection to disabled:

 $ nmcli connection modify Example ipv6.method "disabled"

As a final step let’s restart both NetworkManager and the connection itself:

$ sudo systemctl restart NetworkManager

$ nmcli connection up Example

Verify that everything is properly setup

Let’s enter the ip address show command to display the IP settings of the device:

$ ip address show enp1s0
2: enp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 52:54:00:6b:74:be brd ff:ff:ff:ff:ff:ff
    inet 192.0.2.1/24 brd 192.10.2.255 scope global noprefixroute enp1s0
       valid_lft forever preferred_lft forever

If no inet6 entry is displayed, IPv6 is disabled on the device.

Another way to verify the correct setup is by checking that the /proc/sys/net/ipv6/conf/enp1s0/disable_ipv6 file now contains the value 1:

$ cat /proc/sys/net/ipv6/conf/enp1s0/disable_ipv6
1

References