[Kea-users] host reservation vs. leases

[Thomas Andersen]

Thanks for the answer.
I get your points and as you said, it seems safe to do it that way.

In case I want to force it through faster I can just delete the lease from the mysql as I did this time.
I turned of laptop1 and it will not be used anymore so I should not be in risk of duplicate addresses.


Br,
Thomas

On 01/06/16 21:24, "kea-users-bounces at lists.isc.org on behalf of Tomek Mrugalski" <kea-users-bounces at lists.isc.org on behalf of tomasz at isc.org> wrote:

>On 01.06.2016 20:57, Thomas Andersen wrote:
>> When assigning IP for a client, will dhcp lease always overrule host 
>> reservation?
>It's complicated. In general, adding reservations for an address that is
>used by someone else it a bad idea. Kea will sort that out, but it needs
>some time for that (up to 2x renew-timer).
>
>If you added reservation for an address that is currently leased by
>someone else, Kea will sort that out eventually. Existing user of the
>address will not be able to renew it. laptop2 will get a
>different address until the reserved address is in use by laptop1.
>
>This is explained in
>http://git.kea.isc.org/~tester/kea/guide/kea-guide.html#reservation4-conflict.
>
>> My scenario is as follows:
>> 
>> My laptop (laptop1) had a host reservation for a specific IP.
>> 
>> I then get a new laptop (laptop2) and therefor change my host 
>> reservation to match the mac address for laptop2.
>> 
>> For some reason I don’t get the intended IP assigned for laptop2. I 
>> found out that there was an active lease for that IP by laptop1 who
>> had it assigned by host reservation prior.
>> 
>> Is this working as intended?
>Yes.
>
>> I expected, that because of the change in the host reservation, KEA
>> would ignore the current leases and assign the IP to laptop2 despite
>> of the lease for laptop1.
>That wouldn't work. Just because you changed reservation, the laptop1
>will not magically stop using the address. laptop1 still thinks he's
>entitled to use the address he got for its lease lifetime. Had Kea
>assigned it to laptop2 as you suggested, laptop2 would discover
>duplicate addresses, would report to Kea that the address is declined
>and the reservation wouldn't work anyway.
>
>So what Kea will do:
>1. try to assign reserved address to laptop2, but discover it's used by
>laptop1. will temporarily assign a different address to laptop2.
>2. when laptop1 tries to renew, it is NAKed.
>3. The laptop1 will restart and get a different address. At this point
>the address that was "occupied" by laptop1 becomes free.
>4. Once laptop2 renews, it is also NAKed.
>5. laptop2 restarts. Kea now sees that it has a reservation and that the
>address is free, so assigns it to laptop2.
>
>This is not the fastest recovery procedure, but the safest one. It's
>also fully autonomous, so does not require any manual intervention.
>Personally I think about this as Kea cleaning up the mess sysadmin did :)
>
>Hope that helps,
>Tomek
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