Does DHCP server take IPs back from sleeping systems before its lease expires?

David W. Hankins David_Hankins at
Mon Dec 10 16:16:57 UTC 2007

On Fri, Dec 07, 2007 at 12:28:40PM -0400, Bruce Hudson wrote:
>     You are correct. There is no provision in the DHCP protocol to take
> a live lease away from a client. If this is an issue, the answer is to
> use shorter leases.

This is true, but I wanted to mention there's a tool in 3.1.0 that
makes it easy to hand out shorter lease times.  From 3.1.0's relnotes;

- A new dhcp server option 'adaptive-lease-time-threshold' has been added
  which causes the server to substantially reduce lease-times if there are
  few (configured percentage) remaining leases.  Thanks to a patch submitted
  from Christof Chen.

So this is a tool that starts handing out min-lease-time to clients
when the pool is getting low.  This applies to renewing clients as
well as newly binding clients.  The upside is that you'll get leases
to expire faster if boxes go offline.  The downside is you get a lot
more DHCP activity (so you need to be careful not to overload).

Ash bugud-gul durbatuluk agh burzum-ishi krimpatul.
Why settle for the lesser evil?
David W. Hankins	"If you don't do it right the first time,
Software Engineer		     you'll just have to do it again."
Internet Systems Consortium, Inc.		-- Jack T. Hankins

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