As you know Chromecast uses Google DNS as default. Only very few routers can bypass this and one of them is DD-WRT (www.dd-wrt.com).
Note: Some of our users mentioned that following dd-wrt setup is not working properly on their network. In this case we suggest you setup STATIC ROUTING on your router. Please find all Chromecast DNS Setup Troubleshoot information here.
In order to use Chromecast with Smart DNS Proxy you will need further setup on your DD-WRT router.
1. Go to http://192.168.1.1. This is default dd-wrt admin panel IP. If you have changed it in your router, please use your own internal IP address.
2. Login to your router. Default credentials are root/admin.
3. Go to Setup > Basic Setup > Network Setup > Network Address Server Settings (DHCP).
4. Set DNS to 18.104.22.168 and 22.214.171.124.
5. Click Apply Settings.
6. Go to Services > Services > Services Management > DNSMasq > Additional DNSMasq Options and Enter the following in the text box:
7. Click Apply Settings.
8. Go to Administration > Commands.
iptables -t nat -A PREROUTING -d 126.96.36.199 -j DNAT --to-destination 188.8.131.52
iptables -t nat -A PREROUTING -d 184.108.40.206 -j DNAT --to-destination 220.127.116.11
10. Click Save Firewall.
11. Click Save Startup.