[Kea-users] Host Reservations flexability

Klaus Steden klausfiend at gmail.com
Thu Apr 13 18:45:01 UTC 2017

We had a similar problem, and our approach was to define a custom DHCP
attribute (ignored, but there for comment purposes) and generate the subnet
ID programmatically based on the contents of said comment using a hash
function to create a unique 32-bit integer.

e.g., "rack 41 VLAN 200" and "rack 42 VLAN 200" should hash to different
numbers, so when you generate your scope definitions, you know what the
subnet ID is ahead of time, and can easily derive it based on the label you
gave to each scope.

And yes, strong agree from me -- Kea is awesome, and it was a huge windfall
for our design when we found out about it.


On Thu, Apr 13, 2017 at 9:57 AM, Jason Guy <jguy at cumulusnetworks.com> wrote:

> Hi folks,
> Well, I re-read a few threads related to using the host reservations to
> only supply hostnames for specific known hwaddrs. We have many devices in
> the lab, and frequently move devices in the racks, erase and reinstall, so
> the hwaddr is the only constant. Each rack of equipment has a separate
> top-of-rack switch and subnet, so specifying the subnet_id in the host
> table is not useful. Ultimately it seemed logical that if a subnet_id was
> NOT specified, the hwaddr would be globally known.
> Currently I am using Kea 1.1, and like in the other email threads,
> specifying ONLY the hostname and hwaddress in the host table does not work.
> However, if I add a subnet id, things start working. Is there any way
> (aside from using Hooks), to have the server do an unconstrained lookup in
> the host table for the incoming hwaddr? Something like this:
> SELECT * FROM host WHERE dhcp_identifier = 'discovery_hwaddr' LIMIT 1
> Even if there was a well-known subnet_id that is used for unassigned host
> entries, it would be good. Seems to me that the subnet_id for a host entry
> should be a mandatory field, if it is not usable when left NULL.
> Other than this little snag, I really like Kea, and I think it is a HUGE
> step forward. I am using it with PowerDNS, and it is nice having everything
> in a database. :)
> Thanks,
> Jason
> _______________________________________________
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> Kea-users at lists.isc.org
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