[Kea-users] DHCPv6 Relay from PicOS

[Justin Thomas]

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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