i can deploy machines with two NICs. the first interface uses PXE/DHCP. but I fail to configure the second interface to just have it DHCP. it should then just use the external-to-maas DHCP
After commissioning the machine, does the interface show as connected on the right vlan/subnet from the external DHCP?
If that’s the case, configuring the interface to “DHCP” will make it acquire an IP from the external DHCP (as opposed to the “Auto assign” which means MAAS will assign an IP before deployment).