forget leases

Mark Sandrock sandrock at
Thu Jul 23 15:15:43 UTC 2015

In the Infoblox product, which is based on
ISC DHCP, expired leases can be scavenged,
after a specified time has elapsed.

Setting scavenging to be done immediately
would seem compatible with what the OP
is wanting.

I have no connection with Infoblox other
than working with their DDI product, and
hope it's okay to mention them.


> On Jul 23, 2015, at 8:25 AM, Niall O'Reilly <niall.oreilly at> wrote:
> On Thu, 23 Jul 2015 09:30:56 +0100,
> richard lucassen wrote:
>> Is it somehow possible to create a pool that "forgets" which ip address
>> had been assigned to a particular host once the max-lease-time has
>> expired?
>> Goal: I want to have a pool from:
>> to
>> The first host gets 128, the 2nd 129 etc. The max-lease-time is 300s. I
>> switch off the two hosts. After 10 minutes I take two different hosts.
>> Now I would like that dhcpd assigns ip 128 and 129 again to the new
>> machines.
>  IIUC, your goal is not compatible with the usual reading of the
>  following extract from RFC2131.
> 2.2 Dynamic allocation of network addresses
>   The second service provided by DHCP is the allocation of temporary or
>   permanent network (IP) addresses to clients.  The basic mechanism for
>   the dynamic allocation of network addresses is simple: a client
>   requests the use of an address for some period of time.  The
>   allocation mechanism (the collection of DHCP servers) guarantees not
>   to reallocate that address within the requested time and attempts to
>   return the same network address each time the client requests an
>   address.
>  The second part of the last sentence ("and attempts to return
>  the same network address ...") is key.  Until the pool is exhausted,
>  the server meets this requirement by leasing a fresh, unused address.
>  Best regards,
>  Niall O'Reilly
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