[Dnsmasq-discuss] Dnsmasq on a machine that is a DHCP client

[Simon Kelley]

Kaspar Fischer wrote:
> Hi everybody,
> 
> I have a server in our LAN that runs dnsmasq in order to offer
> DHCP to other machines on the LAN. This works usually great, but
> sometimes the following happens: On a client machine,
> 
>    > ping google.com
>    ping: cannot resolve google.com: Unknown host
> 
> domain-names are not resolved anymore (but I verified that the
> internet itself is accessible: e.g., I can visit Google via
> http://216.239.59.103/). On the server itself (the one that
> runs dnsmasq), 'ping google.com' works perfectly.
> 
> Now, I suspect the following. The server itself uses DHCP to
> obtain an external IP and the IPs of some domain-name servers
> to use. So my guess is that when these change, dnsmasq does
> somehow not realize it and fails. Could this be the cause of
> the problem? Does dnsmasq work on machines that our themselves
> DHCP clients?
> 
> (On the other hand it seems strange that our provider changes
> the DNS servers, right? Maybe the problem lies somewhere else?)

It's possible, but unlikely, that yourproviders are changing nameserver
addresses on the fly, but as long as your DHCP client re-writes
/etc/resolv.conf when that happens, dnsmasq will cope. It checks the
mtime of /etc/resolv.conf and will re-read it automatically if it
changes. There will be evidence in the log if this happens.

The best way to chase this problem is to enable query-logging in
dnsmasq, and look in the system log when the problem occurs.

Cheers,

Simon.

> 
> Many thanks,
> Kaspar
> 
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