[Dnsmasq-discuss] dnsmasq always answer dhcp NAK

Albert ARIBAUD albert.aribaud at free.fr
Fri Jan 20 20:25:00 GMT 2017

Le Fri, 20 Jan 2017 11:20:17 -0800
"Nikita N." <nikitan at operamail.com> a écrit:

> Hi,
> I would like to know what is the setting, to force dnsmasq to *ALWAYS*
> answer every wrong/bugged DHCP Request, with a standard DHCP NAK.
> I have a bugged client which randomly (bugged driver) sends DHCP
> Requests with a wrong/bugged IP, dnsmasq default behavior is not to
> answer nothing: unfortunately when that happens the client hangs
> forever waiting for the DHCP answer (only workaround is reboot).
> Now, I want to force dnsmasq to answer NAK to every wrong/bugged DHCP
> request incoming (instead of keeping silent).
> Thanks.

Hi Nikita,

As per 'man dnsmasq', what you want is probably --dhcp-authoritative.
The man page says this about it:

	Should be set when dnsmasq is definitely the only DHCP server
	on a network.  For DHCPv4, it changes the behaviour from strict
	RFC compliance so that DHCP requests on unknown leases from
	unknown hosts  are  not  ignored.  This  allows new hosts to
	get a lease without a tedious  timeout  under all
	circumstances.  It  also allows dnsmasq to rebuild its lease
	database without each client needing to reacquire a lease,  if
	the  database is  lost.  For DHCPv6  it  sets  the  priority in
	replies to 255 (the maximum) instead of 0 (the minimum).

Note however that this will do what you want or not, depending on what
you mean by 'bugged'. If you mean "a request that could be legitimate
in some circumstances but is not valid here", then --dhcp-authoritative
will do the job. If you mean "a request which may have been randomly
damaged" then there's no way dnsmasq will catch all these.


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