[Kea-users] DHCPv6 replies using the wrong source address

[Luiz Amaral]

Hello people,

I'm running Kea DHCP6 1.9.8 on Debian Buster and ran into an issue when
running it behind a load balancer.

In the host running Kea, I have two different IPv6 addresses:
2a00:xxxx::3, assigned to eth0 and 2a00:xxxx::1:3, assigned to the
loopback interface.

My DHCPv6 relay (2a00:xxxx:3::63) forwards requests to the
2a00:xxxx::1:3 address, via the load balancer. 

When I have "eth0/2a00:xxxx::3" and "lo/2a00:xxxx::1:3" in the
interfaces-config section of my Kea configuration, Kea is answering the
requests, but with the IP address of eth0, instead of the IP address of
lo, which was the destination of the request.
22:21:27.051056 IP6 2a00:xxxx:3::63.546 > 2a00:xxxx::1:3.547: dhcp6
relay-fwd
22:21:27.051550 IP6 2a00:xxxx::3.547 > 2a00:xxxx:3::63.547: dhcp6
relay-reply
22:21:35.133247 IP6 2a00:xxxx:3::63.546 > 2a00:xxxx::1:3.547: dhcp6
relay-fwd
22:21:35.133832 IP6 2a00:xxxx::3.547 > 2a00:xxxx:3::63.547: dhcp6
relay-reply

I have also tried removing the eth0 entry from the interfaces-config
option, but that made things even worse, as now I get an error in the logs:
Jun 22 23:10:49 hostname kea-dhcp6[15658]: ERROR DHCP6_PACKET_SEND_FAIL
failed to send DHCPv6 packet: Interface eth0/2 does not have any
suitable IPv6 sockets open.
Jun 22 23:10:51 hostname kea-dhcp6[15658]: ERROR DHCP6_PACKET_SEND_FAIL
failed to send DHCPv6 packet: Interface eth0/2 does not have any
suitable IPv6 sockets open.

Does Kea have an option to define the source address for outgoing
packets or is there a way to achieve what I am trying to do?

Thank you,
Luiz.