This post will explain ddwrt dnsmasq caching dns server configuration

Using a ddwrt dnsmasq caching dns server lets machines in your LAN resolve DNS from a machine inside your local network, ultimately reducing the time to resolve an IP address from a domain name. If there is a result in your LAN’s dns cache then it is served from inside your LAN, if a result is not available, then the DNS caching machine will query an external DNS service and store the result so that it is available inside your LAN.