[Kea-users] Handling of Prefixdelegation hints

[Darren Ankney]

Hi Ede,

I am not sure I understand what you are asking here but if the client
is being allocated 2001:dead:beef:aa80::/57 this should be no
surprise.  This prefix pool:

       "pd-pools": [
         {       "prefix": "2001:dead:beef:aa00::",
                 "prefix-len": 56,
                 "delegated-len": 57
         } ]

contains two /57 prefix:

2001:dead:beef:aa00::/57
2001:dead:beef:aa80::/57

The client seems to have sent a hint for 2001:dead:beef:aa80:: as
shown in this log message:

DEBUG DHCP6_PROCESS_IA_PD_REQUEST duid=[00:..], tid=0x..: server is
processing IA_PD option with iaid=.. and hint=2001:dead:beef:aa80::

Then you said:

"And of course that upper aa80 net is finally being delegated, despite
the client requesting the lower of the two."

But that doesn't seem to be the prefix for which the client sent a
hint as was shown in the provided log message.

I am confused.

Thank you,
Darren Ankney

On Thu, Aug 8, 2024 at 6:59 AM Ede Wolf <listac at nebelschwaden.de> wrote:
>
> Hello,
>
> new to kea I am having a /56 network, that is being delegated downstream
> by kea in two /57 nets.
> Kea seems to assign those two subnets in a round robin fashion to
> clients, so to have a group of clients receiving a certain subnet, I am
> using prefix hints containing the netid desired with the /57 length.
>
> According to my limited understanding of wireshark, those hints are
> being sent by the client, but seemingly ignored by kea.
>
> The question is, is this likely to be a misconfiguration or sloppieness
> on my side or just works as designed? I have found astonishingly little
> about prefix hints and kea, but maybe my google skills lack as well.
>
> I am running kea-2.2 as shipped by debian 12
>
>  From the client solicit:
> A Prefix
>      Option: IA Prefix (26)
>      Length: 25
>      Preferred lifetime: 0
>      Valid lifetime: 0
>      Prefix length: 57
>      Prefix address: 2001:dead:beef:aa00::
>
>
> But from the server logs:
> DEBUG DHCP6_PROCESS_IA_PD_REQUEST duid=[00:..], tid=0x..: server is
> processing IA_PD option with iaid=.. and hint=2001:dead:beef:aa80::
>
>
> And of course that upper aa80 net is finally being delegated, despite
> the client requesting the lower of the two. And this is a
> testenvironment, so the pools are certainly not exhausted. Would be kind
> of impossible anyway.
>
> The subnet configuration is pretty much bare minimum:
>
> {
>          "subnet": "fde1:dead:beef:16::/64",
>          "interface": "eth0",
>          "id": 11,
>          "pools": [ { "pool":  "fde1:dead:beef:16::12 -
> fde1:dead:beef:16::ffba" } ],
>          "pd-pools": [
>          {       "prefix": "2001:dead:beef:aa00::",
>                  "prefix-len": 56,
>                  "delegated-len": 57
>          } ]
> }
>
>
> Thanks
>
> Ede
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