DD-WRT serving additional DNS servers instead of just the router’s IP

I have a DD-WRT (using DD-WRT v24SP2-MULTI (03/21/11) std) router set up with DNSMasq to resolve certain domains to internal addresses and pass everything else thru. The router itself is configured to use Google’s public DNS servers to resolve addresses.

My setup screen looks like this:

My problem is that when a DHCP client connects, they get the router plus Google’s two DNS servers as the assigned DNS servers:

This is a problem because sometimes wireless clients try to resolve a domain that is supposed to point to an internal IP address and end up getting an external ip instead because for whatever reason their request is sent to 8.8.8.8 instead of to the router.

I don’t want the router to serve anything but its own IP as the DNS server. Is that possible?

It's good that you're using DNSMasq.

You can configure what you want in the Services (> Services) tab, in the DNSMasq > Additional DNSMasq Options box, but first, you'll want to clear those Static DNS fields.

Add the following to the DNSMasq options box:

dhcp-option= option:dns-server, 192.168.10.10 # DHCP option 006

server = 8.8.8.8 # DNSMasq will use these servers for forwarding the DNS requests that it can't serve
server = 8.8.4.4

Info taken from the official DD-WRT site: http://www.dd-wrt.com/wiki/index.php/OpenDNS

It appears you can set the remaining dns servers to non-routable IPs (in my case 10.0.0.0 & 10.0.0.1) and it will squeeze out your ISPs DNS servers with these non-routables. So far for me it seems to be working without any delay waiting on the non-existent DNS servers.

I am not using DDWRT, so this is half-question / half-answer.

The manual DNSMasq as DHCP server says in the section "Extra DNSMasq options" :

There are some extra options in the web interface for DNSMasq that you can set by entering them in Additional DNSMasq Options on the "Services" tab.

If you wish to pass through the DNS servers from your ISP, you can use the following parameters:

dhcp-option=6, x.x.x.x, y.y.y.y

where x.x.x.x = DNS1 y.y.y.y = DNS2

This seems to mean that passing the ISP servers is optional, so locating and deleting the above line should turn it off.

If you do not want clients to reach external DNS do not put their addresses in your DHCP server config.

I suppose you wanted to add (eventually faster) google's DNS servers in a configuration of external DHCP Client (where DNSMASQ would take it's DNS client preferences)

Extra:

You have to add extra (all) DNS servers to WAN link configuration. DNSMasq will use them and never ones DHCP client would acquire from provider.