AsusWRT: block Google DNS with iptables

By default, every Google device uses the following configured DNS-servers: 8.8.8.8 8.8.4.4 But I don’t want my guests, who can use my WiFi, to let Google phone home and give information about who visits my network. I use iptables to block those DNS-requests. The firewall rejects all the DNS-requests that would be sent to Google. …