DHCP and timezone options

H. Peter Anvin hpa at zytor.com
Wed Dec 27 05:48:47 UTC 2017

On 12/13/17 22:24, Richard Laager wrote:
>> it would also be
>> interesting to have the dhcp-renewal-time capped to the point of the
>> next TZ transition, to force it to renew the lease and thus get the
>> updated time-offset option.
> This too would be interesting. Right now, I have to settle for
> compromise lease times that feel too long around the DST transitions and
> too short otherwise.
> One concern I have would be large scale installations. If all the DHCP
> leases were capped to the fixed boundary, it could create a thundering
> herd of renewals. My deployment is not large scale, so I have no
> experience here.

Right, it is probably necessary to give at least the option of a fuzz
interval, so that the renewal-time expires randomly within a specified
window after the transition.

It is also worth noting that this is the only part of this which really
requires any kind of support from within dhcpd itself; the rest can at
least in principle be done with external scripts.  However, emulating a
deadline using an interval (since dhcp-renewal-time represents an
interval) is always cantankerous, although it can be done -- at the cost
of an increasing number of SIGHUPs as one approaches the transition time.

I might still try to hack that up as a proof of concept, though, in case
you or someone else is interested in trying it out.


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