[Dnsmasq-discuss] Can not set lease time to less than 2m

[Tomas Hozza]

On 02/25/2015 09:04 AM, Albert ARIBAUD wrote:
> Bonjour Tomas,
>
> Le Wed, 25 Feb 2015 08:24:25 +0100, Tomas Hozza <thozza at redhat.com> a
> écrit :
>
> > On 02/24/2015 05:26 PM, Jim Alles wrote:
> >> You must have a very small network and very special requirements?
> > It was for dhcp client testing purposes.
> >> From the man pages for dhcp-range:
> >>
> >> Enable the DHCP server. Addresses will be given out from the range
> >> <start-addr> to <end-addr> and from statically defined addresses given in
> >> *dhcp-host *options.
> >> If the lease time is given, then leases will be given for that length of
> >> time. The lease time is in seconds, or minutes (eg 45m) or hours (eg 1h) or
> >> "infinite". If not given, the default lease time is one hour.
> >>
> >> The minimum lease time is two minutes.
> > Ahh, Thank you. I was looking for "2m" and didn't see this statement.
> >> For IPv6 ranges, the lease time maybe "deprecated"; this sets the preferred
> >> lifetime sent in a DHCP lease or router advertisement to zero, which causes
> >> clients to use other addresses, if available, for new connections as a
> >> prelude to renumbering.
> >>
> >> On Tue, Feb 24, 2015 at 10:11 AM, Tomas Hozza <thozza at redhat.com> wrote:
> >>
> >>> Hi.
> >>>
> >>> Even though I configure dnsmasq to git leases
> >>> e.g. for 1 minute it always configures it self
> >>> with 2m lease time. I was not able to get under
> >>> 2m, however if the value is greater than 2m, dnsmasq
> >>> configures itself correctly.
> >>>
> >>> using:
> >>> ...
> >>> dhcp-range=192.168.99.2,192.168.99.254,1m
> >>> dhcp-range=fd00:dead:beef:55::100,fd00:dead:beef:55::1ff,1m
> >>> ...
> >>>
> >>> gives:
> >>> ...
> >>> dnsmasq-dhcp: DHCP, IP range 192.168.99.2 -- 192.168.99.254, lease time 2m
> >>> dnsmasq-dhcp: DHCPv6, IP range fd00:dead:beef:55::100 --
> >>> fd00:dead:beef:55::1ff,
> >>> lease time 2m
> >>> ...
> >>>
> >>> Why it is so? Seems like a bug IMHO.
> >>>
> >>> Regards,
> >>> --
> >>> Tomas Hozza
> >>> Software Engineer - EMEA ENG Developer Experience
> >>>
> >>> PGP: 1D9F3C2D
> >>> Red Hat Inc.                               http://cz.redhat.com
> >
> > Anyway, my question why is this so and why is the user hard-limited?
> > Is there some technical reason behind the limit?
Thank you for answer.
> I guess part of the answer is that the DHCP RFC 2131, while actively
> not defining a minimum lease time, does specify various timings no
> smaller than 60 seconds (e.g. 3.2 item 4, or 4.4.5); with a lease time
> of less than 2 minutes, these various timings could not be respected.
Yes, that makes sense. Thank you for pointing me to the RFC sections.
> (Besides, the smaller the lease time, the bigger the bandwidth DHCP uses
> for a reason (IP address change for a given host) that is not supposed
> to happen just every minute. I, for one -- besides welcoming our insects
> overloards -- would like to know what the use case can be for a lease
> of less than 120 seconds.)
Only some testing scenarios, like DHCP client software testing. Otherwise
I can not think of any useful scenario.
> > Thanks!
> >
> > Regards,
>
> Amicalement,
>
Thank you.

Regards,
-- 
Tomas Hozza
Software Engineer - EMEA ENG Developer Experience

PGP: 1D9F3C2D
Red Hat Inc. http://cz.redhat.com