[Kea-users] Host reservations in DB

[Михаил Ермаков]

Hello Tomek.

Thanks for answer. Really useful!

> On 18.12.2015 07:12, Михаил Ермаков wrote:
>> Hi everybody!
>>
>> It's not clear for me how Kea stores address reservations of hosts.
>> There is something about it in 1.0.0-beta release notes "Leases and
>> (DHCPv4)host reservations stored in MySQL or Postgres".
> Does it say MySQL or Postgres? Uh oh, in this case it's a mistake.
> Storing host reservations is supported in MySQL only.
>
>> Ok. I use 0.9.2. So... I can add record to PostgreSQL with appropriate
>> values (address, hwaddr, lifetime...) and my PC will get this address.
> Yes. What you can do in 0.9.2 is to add, modify or delete leases.
>
>> There is no lease expiration mechanism in 0.9.2.
> There is not. The expired leases can be picked up and reused for other
> clients, though.
>
>> My record would be in database forever.
> No. It won't be there forever. There are two ways in which this lease
> could go away. First, a host that received it may send Release and it
> will cause the server to delete the lease. Second, if the lease lifetime
> passes without the client renewing it, the lease will become expired. It
> will still be in the DB, but the server is allows to reuse it for other
> hosts.
>
>> Is it host reservation?
> No. Leases represent current state of the address pool: what is leased
> to who. You can think about this as a dynamic thing. An address X
> currently belongs to client Y, but it may be reassigned to client Z
> after client Y releases it or goes away and the lease expires.
>
> Host reservation is something different. It's explained in Kea User's
> Guide, section 7.3
> (http://git.kea.isc.org/~tester/kea/guide/kea-guide.html#host-reservation-v4).
> Host reservation is an instruction to the server that address X is
> reserved for client Y and nobody else is allowed to get this address.
> The server will not assign it to anyone else, even if the client Y does
> not currently use it.
>
> This functionality has been supported for a long time (from 0.9 IIRC).
> Host reservations are defined in the configuration file. What was added
> in 1.0.0-beta is the ability to store this information in MySQL. See
> hosts table.
>
> Once again to clarify, storing host reservations is not supported in
> Postgres yet. There's a tentative plan to add it to 1.1.
>
>> What I understand wrong? Why I shouldn't add this records to DB?
> I assume that by 'this' you mean records in leases table, right? You can
> add, modify or delete them, but you need to understand the lifecycle of
> the lease. If you don't know what you are doing, you can hurt yourself
> easily.
>
> If you want to do host reservations and keep it in DB, you should use
> 1.0.0-beta and use MySQL. Make sure you configured hosts-database entry
> (see Section 7.2.3:
> http://git.kea.isc.org/~tester/kea/guide/kea-guide.html#idp64613328).
> Then, put information about your hosts in hosts table. The server will
> use it when the client comes and will generates leases based on your
> host reservations. Once the client goes away or sends Release, the
> leases may disappear. But the host reservation will be there and it will
> prevent the server from assigning this address to anyone else.
>
> Hope that helps,
> Tomek
>
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