Cleanup leases?

Jeff A. Earickson jaearick at
Tue Sep 26 14:26:07 UTC 2006

On Wed, 27 Sep 2006, Glenn Satchell wrote:

> Date: Wed, 27 Sep 2006 00:17:22 +1000 (EST)
> From: Glenn Satchell <Glenn.Satchell at>
> Reply-To: dhcp-users at
> To: dhcp-users at
> Subject: Re: Cleanup leases?
>> Date: Tue, 26 Sep 2006 10:03:56 -0400
>> From: "B. Cook" <bcook at>
>> To: dhcp-users at
>> Subject: Cleanup leases?
>> Hello All,
>> I have a /25 defined for about 64+ laptops, and for low public usage
>> here at the library..
>> today I have started to receive the 'no free leases' entry in the logs..
>> I am going in and removing leases that ended about 20+ days ago..
>> How can I keep this file cleaned up so that people that need leases will
>> get them back from people that are no longer using them?
>> Thanks in advance.
>> - Brian
> Hi Brian,
> No need to manually clean up the file. The dhcp RFC (2131 I think) says
> that the dhcp server must try really hard to give the same IP address
> to a client.
> dhcpd does this by remembering even expired leases so that if that
> particular client came back it could give it the same address it had
> before.
> When a client requests a lease dhcpd tries to match it with an existing
> lease if possible. If it can't then it selects a free lease. If there
> are no free leases then it selects the least recently used lease, frees
> that, and gives that address to the client.
> If you are getting no free leases, and you have a transient client
> base, then perhaps a shorter lease time would work better for you. This
> can be done by setting max-lease-time to something suitable, perhaps an
> hour or so?
> Otherwise what is the size of your range of addresses that you are
> allocating from?
> If none of this helps, then perhaps post your dhcpd.conf, plus dhcpd
> version and platform (eg linux, bsd, solaris, etc).

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
the summer we have summer programs with visitors that come and go.  If
we forget to lower our lease time at the beginning of August, then we
run out of leases in the dorms come September because old info from 
summer visitors is still in the lease pool.  Hence my perl script to
clean dorm leases by force at the end of August before students return.

Jeff Earickson
Colby College

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