DHCP via dnsmasq: client machine not receiving nameserver

Last night I set up dnsmasq on the Western Digital My Book World Edition, a NAS that acts as a server at our home.

I ran up against a problem: one of the client machine (my laptop) was not changing its nameserver settings. It would get an IP address via DHCP just fine, but the nameserver settings were either not being transmitted or not being received properly.

If I had been in my right mind, I would have tried a different machine as client to find out if the problem was on the server side or on the client side. As it stood, I kept examining the server side, but found nothing wrong there.

Nevertheless, it eventually occurred to my clouded mind that I could look in the log on the client side. Eureka!

Nov 17 20:45:34 r400 dns-resolver: ATTENTION: You have modified 
/etc/resolv.conf. Leaving it untouched...
Nov 17 20:45:34 r400 dns-resolver: You can find my version in 
/etc/resolv.conf.netconfig

True, I had modified /etc/resolv.conf -- no argument there. And when I looked in /etc/resolv.conf.netconfig, I saw that the nameserver settings from dnsmasq were there, but of course ineffectual.

The problem went away when I deleted /etc/resolv.conf (my modified version) and then disconnected/reconnected the network cable to the laptop. This let NetworkManager did its thing. After that, a new /etc/resolv.conf appeared with the correct nameserver settings.