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I have a device, in a LAN, behind a router, that runs a linux and need to provide it with an internal DNS server, to resolve names for its own internal applications (it's OpenWRT-based).

The reason to do this is that for some queries, the DHCP-provided stuff doesn't seem to work as expected and some of the client apps get a timeout (sorry for the lack of details, but I'm pretty sure about this as wireshark captures prove some DNS queries are not correctly responded).

I don't intend to run a DHCP server in this device, just local DNS server.

I have a basic knowledge about DHCP, DNS and their handshakings, and I'm not sure how this scenario works with dnsmasq: I configured the DNS server -in the device- with an external public nameserver in its list of servers, expecting (maybe wrongly, I don't know) for it to override the nameservers provided by the DHCP/router/ISP (being the device a DHCP client in this case).

The /etc/resolv.conf file just has the nameserver 127.0.0.1 line, and everything seems to work as I expect.

But what happens if any external DNS is down? Will it fallback to that provided by the DHCP handshaking?

I think put in other words the question would be: when dnsmasq has a list of servers, will it use the DHCP DNS settings?

Hope this is clear.

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From what I could see, it seems that dnsmasq works this way:

  • it puts itself as the dns server to use in the regular resolv file (for instance, in my OpenWRT installation, it's /tmp/resolv.conf);
  • it starts with an option to set a resolv file (--resolv-file, pointing to /tmp/resolv.conf.auto in OpenWRT), for its internal use, where custom name servers and those provided by the DHCP server are set in a list.

So, in short, it keeps track of all name servers.

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