[Kea-users] Missing features from dhcp-eval

[Darren Ankney]

Hi Vladimir,

You are correct, I believe.  Kea flex-option hook cannot overwrite
siaddr (next-server) since it isn't a DHCP option.  Do you need
next-server for other clients?  You can set it to an empty string like
so:

"next-server": "",

at the global or subnet level.  See here for further information:
https://kea.readthedocs.io/en/kea-2.4.0/arm/dhcp4-srv.html#next-server-siaddr

Thank you,

Darren Ankney

On Sun, Oct 15, 2023 at 4:41 PM Vladimir Nikolic <vladimir at nikolic.si> wrote:
>
> Thanks Darren.
>
> I'm trying to set up custom next-server and boot-file-name by setting up
> options 66 in 67 through the flex option hook, everything based on
> relaying router ip.
> I can see that KEA server sends both these options properly.
> But PXE (VMware) client properly picks the filename (option 67) but
> wrongly picks the SIADDR ip instead of TFTP server name (option 66).
> I presume flex option hook can't rewrite the next-server (SIADDR) value?
>
> Regards,
> Vladimir
>
> On 2023-10-15 21:35, Darren Ankney wrote:
> > Hi Vladimir,
> >
> > You should be able to do something like this with the flex option
> > hook:
> > https://kea.readthedocs.io/en/kea-2.4.0/arm/hooks.html#libdhcp-flex-option-so-flexible-option-actions-for-option-value-settings
> >
> > Just need to find out what can be tested for.  Is the traffic relayed?
> >  Will there be a specific giaddr for the client in the subnet that you
> > want to set the custom options?  You can test for a specific relay
> > agent IP (giaddr) with pkt4.giaddr == 192.0.2.1, for example.  You can
> > test if a client is a member of the PXEClients class with
> > member('PXEClients').
> >
> > Hope this helps!
> >
> > Thank you,
> >
> > Darren Ankney
> >
> > On Sun, Oct 15, 2023 at 11:40 AM Vladimir Nikolic <vladimir at nikolic.si>
> > wrote:
> >>
> >> Let's say I want to send custom next-server and filename to PXE
> >> clients,
> >> depending on subnet in which they are located.
> >>
> >> In dhcpd, I define a new option, e.g.:
> >> option something-new code 250 = string;
> >>
> >> Then I set its value in some of the subnets:
> >> subnet xyz {
> >>      option something-new "my-value";
> >> ...
> >>
> >> And within a class definition, I can set up options (e.g. next-server
> >> and filename) based on the value of something-new option (defined
> >> within
> >> subnets):
> >> class "PXEClients" {
> >>      match if substring(option vendor-class-identifier, 0, 9) =
> >> "PXEClient";
> >>      if config-option something-new = "my-value"
> >>          next-server my-new-server;
> >>          filename "my-new-filename";
> >>      } else {
> >>          next-server my-old-server;
> >>          filename "my-old-filename";
> >>      }
> >> ...
> >>
> >> So it's one class with different next-server/filename options, based
> >> on
> >> the subnet in which clients live.
> >>
> >>  From what I've seen so far, you can't do something similar in KEA.
> >> You have to define next-server and filename in every of those subnets,
> >> and that will apply to all the clients in that subnet (not just to
> >> those
> >> belonging to PXEClients class).
> >>
> >> Thanks
> >>
> >>
> >> On 2023-10-15 17:18, Darren Ankney wrote:
> >> > Hi,
> >> >
> >> > I'm not entirely sure what you are asking here.  Do you mean that you
> >> > need to add a client to a class based on what subnet was selected?
> >> >
> >> > Thank you,
> >> >
> >> > Darren Ankney
> >> >
> >> > On Fri, Oct 13, 2023 at 12:36 PM Vladimir Nikolic via Kea-users
> >> > <kea-users at lists.isc.org> wrote:
> >> >>
> >> >> Hi,
> >> >>
> >> >> We are struggling with the migration from DHCPD to KEA.
> >> >> Is there any easy alternative to this dhcp-eval feature:
> >> >>
> >> >> config-option option-name
> >> >>       The config-option operator returns the value for the specified
> >> >> option that the DHCP client or server has been configured to send.
> >> >>
> >> >> In DHCPD, we define an option, and then set it up on particular
> >> >> subnets.
> >> >> It can then be used during class evaluation, by config-option feature.
> >> >> In that way, different classes (with e.g. different next-server and/or
> >> >> filename defined) can be assigned to similar clients, just based on
> >> >> the
> >> >> option value set in a subnet definition.
> >> >>
> >> >>  From what we've seen so far, something like that is not possible with
> >> >> KEA.
> >> >> Looks like we'll have to find an alternative solution.
> >> >>
> >> >> Thanks
> >> >> --
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