Enabling DNS Proxy must be done first globally on the Network > DNS > DNS Proxy page and then again on each interface. This provides a gradual control to enable the feature for different network segments independently.
To enable DNS Proxy
For each interface on which to enable DNS Proxy:
Click the Edit icon for the interface on which to enable DNS Proxy. The Edit Interface dialog displays.
Click Advanced.
Select Enable DNS Proxy. This option displays only when DNS Proxy is enabled globally.
Click OK.