[Kea-users] DHCP4 MySQL Host Reservation Troubles

[Marcin Siodelski]

Hi Bryan,

Let me summarize your issue, so as we check if I understand it correctly:

- You have 3 subnets where you have DHCP clients, of which some have and
some don't have static reservations.
- Router (relay agent) will use one of 3 different giaddrs when relaying
messages to the server over a single link (relay-server link) connected
to a particular interface on the DHCP server.
- For clients for which addresses should be assigned dynamically we want
the server to use giaddr to pick the correct subnet.
- For other clients, which have static addresses, it is possible that
the giaddr may vary and in 2 out of 3 cases the client will not have a
subnet corresponding to his static reservation selected. As a result the
client will get a dynamically assigned address, rather than static one.
- You want to define a static reservation for a given client's MAC
address which should be used regardless of the giaddr appearing in a
relayed message.

The problem with this approach is that our host reservations are
strictly associated with a subnet (subnet id) selected for a client.
This selection takes place even before we check for host reservations.
The subnet id (and MAC address) is used as an input to search for static
reservations for a client.

I need to think a bit more about this issue, but for a time being, would
it be simply possible to insert 3 reservations for the same host,
differing by the subnet identifier? In that case, no matter which subnet
id is selected for the client, the server should always find a suitable
reservation. That may be not viable if I misunderstood your use case :-).

This also has an issue that you have redundant information in the
database and this doesn't scale well with many reservations.

Thanks,
Marcin Siodelski
ISC

On 11.05.2016 23:24, Bryan Perry wrote:
> So any guidance from the ISC gurus on this topic? My host reservation
> seems to work fine only if the correct subnet is assigned, but if a
> different subnet (still part of the same shared network) is assigned
> then the client gets a lease from a pool. If I lock down the upstream
> router to only use the XXX.YYY.169.1 giaddr then normal DHCP clients who
> need addresses from the 170 or 171 subnets get nothing.
>
> Can I define multiple non-contiguous address pools inside the same
> subnet declaration to handle both the static and dynamic clients?
>
> I'm stumped. Thanks for any help.
> -Bryan
>
> On 5/10/2016 1:05 PM, Thomas Andersen wrote:
> > Not sure that you can, and I’m not sure it’s how it is intended.
> > But it’s a bit deeper than what i normally deal with.
> >
> > Maybe one of the ISC guys can elaborate.
> >
> >
> > Br,
> > Thomas
> >
> >
> >
> >
> > On 10/05/16 20:58, "kea-users-bounces at lists.isc.org on behalf of Bryan
> > Perry" <kea-users-bounces at lists.isc.org on behalf of bryan at sfcn.org>
> > wrote:
> >
> >> So the question becomes, how do I force it back to subnet 169 when the
> >> DHCPDISCOVER comes in from the .170.1 relay address (which is the same
> >> router) and the hosts entry is for subnet 169?
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