Quarantine addresses for a configurable time
Simon Hobson
dhcp1 at thehobsons.co.uk
Thu Feb 17 10:33:23 UTC 2011
Flavio Poletti wrote:
> simple use case: Alice gets address A and after some time releases
>it. I would like to be able to set a "quarantine-period" during which
>the released address A can only be re-assigned to Alice and to no one
>else. After this period, the address is fully released and can be
>reused for someone else if needed.
>
>Conceptually, it's as if Alice renewed the lease for
>"quarantine-period" seconds instead of releasing it, and it is then
>released after "quarantine-period" seconds unless Alice asks for an
>address again.
>
>Is it possible by simple configuration of ISC's dhcpd? I tried to look
>in the documentation but did not find anything applicable, apart from
>the address hunting algorithm that only gives me some "best effort"
>but no guarantee that address A can be blocked for some time.
As you've observed, this is the standard allocation technique apart
from there being no minimum before an address is re-allocated if
needed. There is no built in method for enforcing a minimum time
before an address is re-used. It would be sub-optimal for most
people, either :
1) There are enough available addresses (relative to the client churn
rate), in which cases Alice's address won't get re-used for some time
or
2) There aren't enough addresses, and so Alice's address will be
needed and to reserve it would "break the network" for some other
client.
There is one method I could see having potential. Newer versions
support reserved leases - these are never re-assigned to another
client no matter how long they've been expired. It would need some
external scripting, but it might be possible to set the reserved flag
on Alice's lease while it is active (or on all new leases, depending
what you are trying to do). Periodically, your script checks the
status of leases, and for those that have been expired for more than
your quarantine period, it unsets the reserved flag and makes them
available for re-allocation.
But I do find myself asking ... Why ?
--
Simon Hobson
Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
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