kea-dhcp4 behaviour question client-class vs reservations

[Darren Ankney]

Hi Philipp,

The keyword "client-class" restricts access to the pool to members of
the class.  It does not assign members of a class to a pool.  See
here: https://kea.readthedocs.io/en/kea-2.4.1/arm/classify.html#configuring-pools-with-class-information
where it says "Similar to subnets, in certain cases access to certain
address or prefix pools must be restricted to only clients that belong
to a given class, using the client-class when defining the pool.".

Thank you,
Darren Ankney

On Fri, Apr 26, 2024 at 5:05 AM Jan-Philipp Snizek
<jan-philipp.snizek at business.uzh.ch> wrote:
>
> Hi
>
> I would like to ask a question regarding precedence behavior of kea-dhcp4.
>
> Let's take this working config:
>
>     "client-classes": [
>        {
>             "name": "pxeclientx64",
>             "test": "option[60].text == 'PXEClient:Arch:00007:UNDI:003016'",
>             "option-data": [
>                 { "name": "vendor-encapsulated-options", "always-send": false },
>                 { "name": "boot-file-name", "data": "SMSBoot\\x64\\wdsmgfw.efi" },
>                 { "name": "tftp-server-name", "code": 66, "data": "my-tftp-server.domain.local" }
>            ]
>        }
>     ],
>     "subnet4": [
>         {
>             "id": 1,
>             "subnet": "172.20.19.0/24",
>             "next-server": "172.20.19.1",
>             "pools": [
>                         { "pool": "172.20.19.120 - 172.20.19.129" },
>                         { "pool": "172.20.19.130 - 172.20.19.139", "client-class": "pxeclientx64" }
>                  ],
>             "reservation-mode": "out-of-pool",
>             "reservations": [
>                 { "hostname": "pxeboot1", "hw-address": "00:e0:4c:68:0a:f1", "ip-address": "172.20.19.150" }
>             ],
>             "option-data": [
>                 { "name": "routers", "data": "172.20.19.1" }
>             ]
>         }
>     ],
>
> If the client with the reservation executes a PXE boot it gets the reserved IP .19.150 and successfully boots PXE.
> The kea-dhcp4 log looks like this:
> Apr 25 13:53:17 hellbox kea-dhcp4[16858]: INFO  EVAL_RESULT Expression pxeclientx64 evaluated to 1
> Apr 25 13:53:17 hellbox kea-dhcp4[16858]: INFO  DHCP4_LEASE_ADVERT [hwtype=1 00:e0:4c:68:0a:c1], cid=[no info], tid=0x2223e0e3: lease 172.20.19.150 will be advertised
> Apr 25 13:53:20 hellbox kea-dhcp4[16858]: INFO  EVAL_RESULT Expression pxeclientx64 evaluated to 1
> Apr 25 13:53:20 hellbox kea-dhcp4[16858]: INFO  DHCP4_LEASE_ALLOC [hwtype=1 00:e0:4c:68:0a:c1], cid=[no info], tid=0x2223e0e3: lease 172.20.19.150 has been allocated for 3600 seconds
> As we can see both matches: pxeclientx64 and the reservation. The client successfully boots pxe.
> I don't understand why the client successfully pxe boots. The client-class "pxeclientx64" is assigned to a pool. It is neither assigned to the subnet4 { id: 1 } subnet declaration nor to the reservation.
> What has precedence over what? How does inheritance work in kea?
>
> Thanks,
>
> --
>
>   Philipp
>
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