[Kea-users] Dhcp6 Prefix Exclude use case question

[Darren Ankney]

Hi Dan,

I don't think that is the purpose of the option, but I suppose if no
device asks for an excluded prefix then the prefix will not be
allocated to any device.  How would you be able to guarantee this?  I
would think a better solution would be to engineer your network
differently such that you don't need to leave off part of the prefix
delegation.  Surely there are plenty of IPv6 subnets to go around to
accomplish this?

Thank you,

Darren Ankney

On Wed, Jun 21, 2023 at 5:09 PM Dan Geist <dan at polter.net> wrote:
>
> Greetings, all. I'm exploring using the "prefix exclude" feature to do something a little different than what it's RFC describes and would like to know if my scenario would work. In the kea ARM, the example config is as follows:
>
> "Dhcp6": {
>     "subnet6": [
>         {
>             "subnet": "2001:db8:1::/48",
>             "pd-pools": [
>                 {
>                     "prefix": "2001:db8:1:8000::",
>                     "prefix-len": 56,
>                     "delegated-len": 64,
>                     "excluded-prefix": "2001:db8:1:8000:cafe:80::",
>                     "excluded-prefix-len": 72
>                 }
>             ]
>         }
>     ]
> }
>
> This allows a device that sends a Prefix Exclude option to be allocated the indicated /72.
>
> In my environment, we'd like to be able to allocate PDs from a block that is discrete from the subnet and in which the very first PD is NEVER assigned, ala:
>
> "Dhcp6": {
>     "subnet6": [
>         {
>             "subnet": "2001:db8:1::/48",
>             "pd-pools": [
>                 {
>                     "prefix": "2001:db8:2::",
>                     "prefix-len": 48,
>                     "delegated-len": 60,
>                     "excluded-prefix": "2001:db8:2::",
>                     "excluded-prefix-len": 60
>                 }
>             ]
>         }
>     ]
> }
>
> Assuming I don't have any dhcpv6 endpoint devices sending the excluded prefix option, does this accomplish what I'm attempting, which is: never use the first /60 from the PD /48 prefix?
>
> Thanks
> Dan
>
> --
> Dan Geist dan(@)polter.net
>
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