Cleanup leases?

Jeff A. Earickson jaearick at
Tue Sep 26 17:42:44 UTC 2006

On Tue, 26 Sep 2006, Sean Kelly wrote:

> Date: Tue, 26 Sep 2006 10:38:05 -0500
> From: Sean Kelly <smkelly at>
> Reply-To: dhcp-users at
> To: dhcp-users at
> Subject: Re: Cleanup leases?
> On Tue, Sep 26, 2006 at 10:26:07AM -0400, Jeff A. Earickson wrote:
>> Well, there are times when lease pools can fill up at edu site because
>> of "big turnover" lease events.  For instance, our dorm lease times are
>> normally 30 days, which works well through out the school year.  But in
> ...
> Thirty days?! What was the justification behind making your lease times so
> long?

I didn't choose the number, our network admin did.  This was after reading
"The DHCP Handbook" by Droms and Lemon.  Why he chose such a long time
is beyond me.
> Our default lease time across the entire network is 2 hours, with a maximum
> lease time of four hours. This includes all residence halls that reside on
> our network. THe theory is that since DHCP attempts to hand out the same
> addresses to returning clients, and since clients generally renew at around
> the halfway point of their lease's lifetime, we don't gain much from having
> longer lease times.
> The only advantage I see to really long lease times is that if DHCP goes down,
> fewer clients are going to be impacted. However, this can be mitigated by
> using DHCP failover. Furthermore, by having shorter lease times we avoid
> the specific problem you mention where high turnover causes us to run out
> of addresses.

When the network guy picked 30 days we didn't have failover.  But we do 
now, and it works nicely.  Maybe I should browbeat him about this, but
he is stubborn.

Jeff Earickson
Colby College

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