[Kea-users] Lease or reservation

Tomek Mrugalski tomasz at isc.org
Mon Oct 10 17:41:55 UTC 2016


W dniu 10.10.2016 o 18:44, Csoke János pisze:
> Yesterday I installed Kea 1.1.0 to my Debian 8.6.0 system and it's
> working fine with Postgresql backend. In my network no dynamical IP poll
> avaiable, I only use reserved IP address for all hosts.
Cool. Thanks for reporting!

> And I have a question.
> 
> When Kea send the reserved IP to the client, it's write this data of
> DHCP respone to the leases SQL table. My question is, If I modify the
> reserved IP for this host in host reservation SQL table and the lease is
> not expire when the client send a new DHCP request, which IP will
> including to the respone? The leased IP or the new reserved IP?
In general, you as a sysadmin should modify reservations and Kea will
sort out the leases for you.

Kea will do its best to honour the reservation, but it may not happen
immediately. If the address that is reserved is available for allocation
(i.e. not used by anyone else), the DHCPv4 server will send NAK first,
which will cause the client to restart its configuration. When it does
that, Kea will assign the reserved IP address. That's because DHCPv4
protocol does not allow to dynamically change the IP address without
going through the full DORA exchange.

It is slightly easier in DHCPv6, where the protocol allows to change the
address without going through Solicit/Advertise, so the renewal will be
sent back with 2 addresses: the one with leased IP with lifetimes set to
0 (that's how DHCPv6 signals that the client must stop using the
address) and the address from reservation with valid lifetimes.

Speaking of conflicts between leases and reservations, there are worse
things one could do and Kea will still be able to recover from it.
You may take a look at Section 7.3.2 Conflicts in DHCPv4 reservations:
http://kea.isc.org/docs/kea-guide.html#reservation4-conflict

or Section 8.3.2 Conflicts in DHCPv6 reservations:
http://kea.isc.org/docs/kea-guide.html#reservation6-conflict

Hope that helps,
Tomek



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