[Kea-users] Client Class for a Specific Subnet

[Darren Ankney]

Hi Isaac,

Your choices are limited at the moment.  You can use the flex option
hook to replace option content based on class membership as described
in the hook documentation:
https://kea.readthedocs.io/en/kea-2.6.1/arm/hooks.html#libdhcp-flex-option-so-flexible-option-actions-for-option-value-settings
There is also this KB article that shows this in action:
https://kb.isc.org/docs/redefining-standard-options though the subject
of the article is actually about sending different content in an
option than it is supposed to carry.

In this case, you could set the "else" portion of your ISC DHCP
configuration as an option in the corresponding subnet in the Kea
configuration.  Make the client a member of the class as you've shown.
Then use the flex option hook to replace the option content if the
client is a member of "ipxe_legacy_netbootxyz".

In the development version 2.7.4, there is the new method called
"Option Class-Tagging":
https://kea.readthedocs.io/en/kea-2.7.4/arm/classify.html#option-class-tagging
that will allow you to tag any option to be sent based on class
membership.  This is an effective replacement for the "if"
functionality in ISC DHCP.  This will first appear in a stable version
in 3.0.0.

Thank you,
Darren Ankney

On Wed, Dec 4, 2024 at 3:48 PM Isaac Brummel <ibrummel at xes-inc.com> wrote:
>
> Hello,
> I'm in the process of migrating an ISC DHCP server to Kea. I'm trying to re-create a feature that we use in the ISC DHCP config to set a boot file name if a specific vendor-class-identifier is met. The ISC DHCP share-network looks like:
>
> shared-network FOOBAR {
>     allow bootp;
>
>     subnet 10.10.10.0 netmask 255.255.255.0 {
>
>         # default PXE boot
>         if substring(option vendor-class-identifier, 0, 20) = "PXEClient:Arch:00000" {
>             filename "ipxe/netboot.xyz.kpxe";
>         } else {
>             filename "ipxe/netboot.xyz.efi";
>         }
>
>
> For Kea I can create the client class just fine, but how can I restrict these client classes to apply only to this subnet? I have other subnets that use a different boot file name. It doesn't seem like using "client-class" in the "subnet4" config would work as that would require a client to meet the classification, when that's not necessary.
>
> "client-classes": [
>     {
>         "name": "ipxe_legacy_netbootxyz",
>         "test": "substring(option[60].hex,0,20) == 'PXEClient:Arch:00000'",
>         "next-server": "10.10.10.5",
>         "boot-file-name": "ipxe/netboot.xyz.kpxe"
>     },
>     {
>         "name": "ipxe_efi_netbootxyz",
>         "test": "substring(option[60].hex,0,20) == 'PXEClient:Arch:00007'",
>         "next-server": "10.10.10.5",
>         "boot-file-name": "ipxe/netboot.xyz.efi"
>     }
> ],
>
>
> Thanks,
>
> Isaac Brummel
> System Administrator
> Extreme Engineering Solutions
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