Hello, I set up a router on an OS zone and use dhcpcd for dhcp6 pd. However, as soon as I inet6 plumb up the interface, dhcpagent kicks in and I need to pkill it before I can start dhcpcd because dhcp6_openudp: Address already in use. I couldn't find a way to prevent dhcpagent to start but maybe I'm on the wrong path?

ipadm(8) may be your friend here.

Since you're bringing up these NICs in-zone, vmadm/vmadmd & friends may be interfering.

In SmartOS zone-networking is done by vmadm(8) parameters. `vmadm get <zone-UUID>` shows what it thinks networking is, and any "inet6 plumb" you do in-zone isn't part of that.

And that was my next question :) I looked at ipadm(8) and vmadm(8) but couldn't find how to replace dhcpagent by dhcpcd, I have "ips": [ "dhcp", "addrconf" ] in my json file. I guess I could set up an smf service but that looks hacky.

Do you want addrconf & dhcp for your vm? That's how the system ones know to start.

You may want to assign a single static IP to the IPv6 NIC you want, and THEN bring up your own services in-zone.