[Dnsmasq-discuss] Repeated assignment, ignored dhcp-host, and failed DNS lookup

[Simon Kelley]

On 08/10/12 17:30, Lovelady, Dennis E. wrote:
> Hi, Simon:
>
> I have all the logs going back to June, 2011.  (That represents about
> 70,000 lines of dnsmasq-related messages.)  What would you like to
> see from those?
>
> The m1330c/w system was on a different network yesterday morning, and
> moved back to this network in the evening.  Absolutely possible that
> it is hanging on to its prior lease, though I didn't think those
> survived a boot after a network switch.  You would absolutely know,
> though, and I take it from your response that that's probably what
> happened.  I'll refresh the lease this PM if not back to "normal" by
> then.

A lease will survive a client reboot, but I'd expect a reboot to cause a 
system to at least confirm a lease. Could you look through your dnsmasq 
logs to see what, if anything dnsmasq logged about this machine when it 
booted up on this network?

>
> How would I know if a rogue DHCP server has appeared on the net?  I'm
> assuming you're on the right track since the answer to the remaining
> question is:

I don't think it's likely, at the moment. My guess is that the DHCP 
server is at the same IP address on both the networks, and when the 
machine came back up, it sent the DHCPINFORM to the DHCP server address, 
then took the response as confirmation that the lease was still valid. 
This is a bit of a gray area, but the client isn't strictly allowed to 
do that: it should send a DHCPREQUEST. (strictly, it should entry 
INIT-REBOOT state)
>

> /var/lib/misc/dnsmasq.leases is empty!!!!

That makes sense: dnsmasq will still reply to DHCPINFORM without a 
lease, and the DHCPINFORM won't create a lease. Once the lease expires 
at the client end, or you force it too, then stuff should re-sync.


If rebooting the client caused it to send only DHCPINFORM requests, then 
we have some grounds to complain to Microsoft.


Simon.