Hello  @Vishnu_Ellusamy ,

Welcome to our community.

TP-Link routers allow you to specify a custom local DNS server for your LAN clients by using the DHCP option, which you are already doing. However, the routers themselves do not support disabling their internal DHCP server to fully delegate DHCP duties to another device (such as your AdGuard server) directly from the router's interface. Additionally, the Internet DNS settings are typically intended for public DNS servers and may not accept local IPs due to validation rules. Your feedback regarding this limitation is valuable, and I will forward your feature request to our product team for consideration in future updates. For now, specifying your AdGuard server as the DNS via the DHCP option is the recommended approach on TP-Link routers.