forget leases

Niall O'Reilly niall.oreilly at
Thu Jul 23 13:25:09 UTC 2015

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

  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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