[Kea-users] KEA DHCPv6 subnet prefixes from upstream IA_PD

[Darren Ankney]

Hi Owen,

I'm afraid I don't have much experience actually using the mechanism.
In your proposed suggestion, I think it would look like this:

“prefix”: "<?include “prefix_file”?>1:/64” {

and the contents of prefix_file would be:

2001:db8:f342:384

with no new line character or spaces.  Would that work?  I don't know.
Perhaps you could test in a lab setting before implementation?

Thank you,
Darren Ankney

On Wed, Jan 15, 2025 at 7:40 AM Owen DeLong <owen at delong.com> wrote:
>
> Can I really substitute part of a string from an include file? Forgive my ignorance, but what would the syntax for that look like?
>
> Imagine: prefix in file is “2001:db8:f342:384” an example representing a /60 typically issued by a certain address stingy cable provider.
>
> Statement needed in kea:
>        “prefix”: “2001:db8:f342:3841::/64” {
>
> Ignoring for the moment, the need to include said prefix fragment in 16x3 places (subnet declaration, pool start, pool end, plus in each reservation), I’m trying to figure out how even this one statement would look:
>
>         “prefix”: <include “prefix_file”>”1:/64” {
>
> Seems unlikely to parse. Can I make a call to concat() in that context and use the include directive as one of its arguments?
>
> I’m not trying to be obtuse, just trying to figure out a practical implementation of your suggestion.
>
> Owen
>
> > On Jan 14, 2025, at 15:27, Darren Ankney <darren.ankney at gmail.com> wrote:
> >
> > Perhaps you could make use of the "include" mechanism?
> > https://kea.readthedocs.io/en/kea-2.7.5/arm/config.html#configuration-files-inclusion
> >
> >> On Tue, Jan 14, 2025 at 2:25 PM Owen DeLong <owen at delong.com> wrote:
> >>
> >> Is there any way to at least template the configuration so that I don’t have to change every occurrence of the prefix in the
> >> Entire file, but rather change a configuration variable that is referenced everywhere?
> >>
> >> I’m presuming some variant of the concat() expression commonly used in client classing might be useful here, but It’s not
> >> Clear to me how widely expressions can be used in a kea configuration file outside of client classes.
> >>
> >> If that capability doesn’t currently exist, it’s probably very much worth adding to the enhancements list.
> >>
> >> Owen
> >>
> >>
> >>>> On Jan 14, 2025, at 10:02, Darren Ankney <darren.ankney at gmail.com> wrote:
> >>>
> >>> Hi Owen,
> >>>
> >>> I can't think of anyway from within Kea to do this.  Kea would have no
> >>> knowledge of what prefix was delegated.  I would say that you would
> >>> need to do scripts or find some consumer device that already does this
> >>> for you (e.g., perhaps one of the ASUS routers?).
> >>>
> >>> Thank you,
> >>> Darren Ankney
> >>>
> >>> On Tue, Jan 14, 2025 at 4:33 AM Owen DeLong via Kea-users
> >>> <kea-users at lists.isc.org> wrote:
> >>>>
> >>>> I’ve got a router running on a linux box using IPv4 NAT, and the KEA dhcp4 configuration is limited, but simple because my only option is to assign static RFC-1918 subnets and NAT them.
> >>>>
> >>>> However, for IPv6, I’m receiving an IA_PD and I’m able to use systemd-networkd to put the prefixes on the interfaces, but I’m stumped how to get KEA to pick up those prefixes to build DHCPv6 pools for address assignment. Sadly, I’ve got a few devices that won’t do SLAAC (yes, I know this is sacrilege, but I lack leverage to move the vendors in question). My clients that speak SLAAC are getting valid information and working.
> >>>>
> >>>> However, I’d like to provide M+O bits and do some reservations and stateful DHCPv6 in some cases. However, I don’t want to have to go in and edit the kea-dhcp6.conf every time the upstream decides to change the delegated prefix, so I’m trying to avoid hardcoding a dynamic prefix into the kea configuration file.
> >>>>
> >>>> Is there currently any way to do this in KEA? I suppose worst case, I can write scripts to update the kea configuration and put them in systemd-networkd hooks so that when the prefix is changed, they update kea, but that feels horribly hacky and I can’t help but think this would be a common implementation situation in the SOHO world.
> >>>>
> >>>> Any pointers or assistance greatly appreciated. If the question is asked and answered, links are appreciated as I haven’t found the answer in any of my searching so far.
> >>>>
> >>>> Thanks,
> >>>>
> >>>> Owen
> >>>>
> >>>> --
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> >>
>