[Kea-users] Flex Options for BOOTP FNAME

[Skyler Blumer]

Are you saying that you're making static host reservations in a DB, and 
are they global reservations? From what I'm seeing you can only make 
reservations at the subnet level in 3.0.

On 12/8/25 1:55 PM, Marcin Jurczuk wrote:
> Hi,
> Please look into historical thread past month from myself. Been there 
> done that. I’ve tried for exactly the same reason for cable modem 
> provisioning.
> As of today flex option only sets “real” dhcp options and can’t set 
> field in dhcp header.
> I’ve end up with cross db syncing by adding records to hosts table 
> with db host backend. This table has column named dhcp4_boot_filename 
> which is exactly that field. Modems work with that.
>
> Regards
>
> On Mon, Dec 8, 2025 at 19:50 Skyler Blumer 
> <skyler.blumer at zitomedia.com> wrote:
>
>     I'm Currently testing with kea 3.0. My end goal is to dynamically set
>     the boot-file-name (legacy BOOTP FNAME field not DHCP option 67)
>     to the
>     CHADDR sent in the request.
>
>     Using the below it will set option 67 to cm/<CHADDR>.bin
>
>              {   "library": "libdhcp_flex_option.so",
>
>                      "parameters": {
>                          "options": [
>                              {
>                                  "name": "boot-file-name",
>                                  "supersede": "lcase(concat('cm/',
>     concat(relay4[2].hex, '.bin')))",
>                                  "csv-format": false,
>                                  "client-class": "docsis"
>                              }
>
>     However when I try to do this in a subnet or class the FNAME is
>     set to a
>     string literal "'cm/', concat(relay4[2].hex, '.bin'"
>
>     "boot-file-name": "lcase(concat('cm/', concat(relay4[2].hex,
>     '.bin')))"
>
>     Is there a way to do this for the legacy FNAME field?
>
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