[Kea-users] DHCPv6 Relay from PicOS

[Darren Ankney]

Hi Jusin,

Three things that might help you here are:

1) You can specify a relay agent in the subnet (see:
https://kea.readthedocs.io/en/kea-2.4.1/arm/dhcp6-srv.html#using-a-specific-relay-agent-for-a-subnet)

2) You can specify an interface-id for a subnet (see:
https://kea.readthedocs.io/en/kea-2.4.1/arm/dhcp6-srv.html#dhcpv6-relays).

3) You can also specify an interface at the subnet level.  I could not
find a specific section about that in the ARM but section 9.4.1 does
show the configuration as an example of what not to do when working
with shared networks (because all subnets must use the same interface
in a shared network).  See here:
https://kea.readthedocs.io/en/kea-2.6.0/arm/dhcp6-srv.html#local-and-relayed-traffic-in-shared-networks

Hopefully one of these will allow you to workaround the problem you are having.

Thank you,
Darren Ankney

On Fri, Oct 4, 2024 at 11:24 AM Justin Thomas
<justin at emeraldbroadband.com> wrote:
>
> Hi folks!
>
>
>
> I’m using PicOS L3 switches to relay DHCPv6 requests to a Kea server. My server is set up like this:
>
>
>
> {
>
>     "Dhcp6": {
>
>         "interfaces-config": {
>
>             "interfaces": ["internal/fde1:8a58:60b7:c23c::10"]
>
>         },
>
> …
>
>         "subnet6":
>
>         [
>
>             {
>
>                 "subnet": "2604:2940:8000:8::/64",
>
>                 "rapid-commit": true,
>
>                 "pools": [ { "pool": "2604:2940:8000:8::/80" } ],
>
>                 "pd-pools": [
>
>                     {
>
>                         "prefix": "2604:2940:8000:2800::",
>
>                         "prefix-len": 54,
>
>                         "delegated-len": 60
>
>                     }
>
>                 ],
>
>                 "reservations": []
>
>             },
>
> …
>
>
>
> The PicOS relay sends data that looks like this:
>
> 08:57:19.802158 internal In IP6 (flowlabel 0x2c0ee, hlim 63, next-header UDP (17) payload length: 167) 2604:2940:8000:8:0:ffff:ffff:fffe.547 > fde1:8a58:60b7:c23c::10.547: [udp sum ok] dhcp6 relay-fwd (linkaddr=ff02::1:2 peeraddr=fe80::f4fa:c4ff:fe8c:f5d3 (interface-ID 000007d0...) (Remote-ID 35098 666c336e77...) (relay-message (dhcp6 solicit (xid=9de569 (client-ID hwaddr type 1 f6fac48cf5d3) (IA_NA IAID:3297572307 T1:4294967295 T2:4294967295) (option-request DNS-server vendor-class) (elapsed-time 65535) (vendor-class) (IA_PD IAID:3297572307 T1:4294967295 T2:4294967295))))
>
>
>
> It's using the IPv6 address assigned to the VLAN associated with the request as the source of the relayed message (2604:2940:8000:8:0:ffff:ffff:fffe), but does not update the ‘linkaddr’ field with that message. I have not yet been able to find a way to adjust the ‘interface-id’ field, so I can’t change that to link to a subnet in Kea. And the value that gets set by PicOS doesn’t seem to be ASCII, so I haven’t found a way to specify that in the subnet declaration in Kea as hex (if that would make sense to do).
>
>
>
> I can adjust the ‘remote-id’ field sent by PicOS (by default it’s omitted, but I have it set in the request above), but I haven’t found a way in Kea to use that as the primary subnet selection criteria. From what I can see, I could use that as part of a class to further filter requests once the subnet is selected, but that’s not what I need.
>
>
>
> Is there any way to configure Kea to use the source address of the relay packet or the ‘remote-id’ as the subnet selection criteria? I also have a request open with FS (who own PicOS) to have them adjust the `linkaddr` field, but I don’t know if they will do that or how long that will take.
>
>
>
> -Justin
>
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