Control D can be configured on most routers with variable degrees of ease, depending on what DNS protocols your router supports, and whether you have a Static IP or not.

Secure DNS

If your router natively supports DNS-over-HTTPS or DNS-over-TLS, this is the easiest (and best) option. Simply input your Device's DNS resolvers into the router interface and you're done. This is the best and preferred method of using Control D, as it's not subject to any of the Legacy DNS limitations.

Unfortunately, most routers do NOT support Secure DNS natively, in which case you have to use the other methods documented below.

Legacy DNS

Most routers do not support Secure DNS protocols, so you're going to have to use Legacy DNS IP addresses associated with the Device you've created in the web panel (be sure to enable the Legacy Resolver Device setting).

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Dynamic IP Warning
This method is subject to your source IP being registered on this Device in the web control panel, so this is best suited for networks with a static IP. If you have a Dynamic IP see Legacy DNS limitations section for solution.

DNS Proxy Daemon (ctrld)

If your router is on a dynamic IP address, or if you wish to use Secure DNS protocols anyway (you really should), you can use the open source Command Line Daemon in order to do this.

Supported Routers

The ctrld daemon currently supports 1 liner installation command on the following routers / firmware:

ASUS Merlin
OpenWRT
DD-WRT
Fresh Tomato
Firewalla
Ubiquiti UDM, UDR, EdgeRouter
GL.iNet
Synology
pfSense / OPNsense

Other routers may be supported, but you have to do some some manual work, which involves:

Making sure ctrld launches on boot / runs as a system service
Steering DNS traffic to the listener

Automatic Install

To do this in the quickest possible way, go to Devices -> Routers section and click the + button. Choose your router vendor or firmware.

Give it a name and set appropriate settings.

Then click Automatic Setup button from the resolver screen and follow the 1 step instruction.

Manual Install

Simply download and run the binary that is appropriate for your router architecture, and follow the instructions in the README on Github. Alternatively, you can use a 1 liner command to install ctrld automatically.