[Kea-users] Flex Options for BOOTP FNAME

[Marcin Jurczuk]

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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