Domain Name Systems (DNS) are like the internet’s phone book. They maintain a directory of domain names (like "google.com") and translate them to IP addresses. Google Nest Wifi and Google Wifi both operate as a DNS proxy. This means the device will automatically offer to receive DNS queries from clients on your network, contact a public DNS server, and respond to your clients with the response. With Nest Wifi and Google Wifi you can set a new DNS server address.
How do I change my DNS server address?
- Open the Google Home app
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- Tap Favorites
Wifi
- Tap DNS.
- Choose your desired public DNS server. If you choose a custom DNS server, enter a primary and secondary server address.
- Tap Save
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Wifi 
.When you type a URL into your browser, your browser looks up the part of the URL that contains the domain name in DNS. For example, if you type “www.google.com” into your browser, your browser asks DNS for the IP address of “google.com.” DNS returns the IP address assigned to Google’s domain name such as 74.125.239.35. Your browser then connects to that IP address, taking you to the webpage.
A helpful analogy is your phone. When you want to call your mom, you select “Mom” from your contact list. Your phone associates the name “Mom” with her phone number and dials it for you.
Google Wifi and Nest Wifi give you 3 options:
- Automatic: This uses Google Public DNS or your Internet Service Provider's (ISP) DNS if certain conditions are met. Automatic is the default DNS selection, although the default may be different depending on how you obtained your device.
- ISP’s DNS: This uses your ISP’s DNS.
- Custom: This lets you specify a custom or third-party DNS. Custom DNS supports two distinct lists of servers, primary and secondary for both IPv4 and IPv6.
Note: Be careful if you choose to use a custom DNS. If you specify a DNS that doesn't work (either the wrong IP or the DNS goes down), none of your connected devices will be able to access the internet (unless they are provided manual-override DNS entries). Your router or primary Wifi point itself will still be able to connect to the internet, allowing you to revert to a different (working) DNS, if you have a phone or tablet that has access to another connection to the internet.