[Dnsmasq-discuss] Query about solving a DHCPNAK issue

Simon Kelley simon at thekelleys.org.uk
Mon Feb 2 20:30:23 GMT 2015


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On 02/02/15 19:50, Brian Haley wrote:
> Hi,
> 
> There have been a number of people chasing an issue in Openstack
> where dnsmasq was sending DHCPNAK's after it was restarted since
> it's being started with --leasefile-ro
> (https://launchpad.net/bugs/1345947).
> 
I guess the first question is why you're giving yourself these
problems in the first place? If you allow dnsmasq to have a lease
file, or keep a lease database otherwise, then you'll have solved the
source of the problem.

> The first solution was to create a script that could be called to
> re-populate the database inside dnsmasq based on the current
> contents of the "hosts" file that had been created
> (https://review.openstack.org/#/c/108272/).

> 
> But then today someone else found the --dhcp-authoritative option 
> (https://review.openstack.org/#/c/152080/) that seems to be an even
> easier solution.  Since when Openstack is managing the DHCP service
> it *is* the authoritative server, this seems like the correct fix.
> Does anyone see any problem with this approach even when there are
> multiple dnsmasq processes being run (for HA), since both are under
> control of the same DHCP authority?


It will probably be fine. The client first unicasts to the DHCP
server, and --dhcp-authoritative means that the server will re-create
the lost lease, rather then erroring. The problem is if the client
broadcasts a renewal. In that case _both_ instances would reply.
Exactly what happens in that case I'm not quite clear, I guess it
would depend on the client. Maybe worth an experiment.


Cheers,

Simon.




> 
> I'm hoping not as this would be a much easier fix.  Thoughts?
> 
> Thanks,
> 
> -Brian
> 
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