Quad9 is a free security solution that uses DNS to protect your systems against the most common cyber threats. Please follow the steps below to configure Ubuntu 16.04 LTS to use Quad9.
From the Ubuntu desktop, select the Network icon (up and down arrows) at top right corner of the screen, and click Edit Connections...
Select the connection that you wish to modify and click Edit
Select the IPv4 Settings tab, set the Method to Automatic (DHCP) addresses only, enter the desired Quad9 IP addresses, then click Save. For more information about which Quad9 service is right for you, please visit our Quad9 IPs and Other Settings page. Quad9 strongly suggests entering both primary and secondary addresses. Multiple IP addresses can be entered in the list by using comas.