Regarding the connection of IPOE, according to the tests before, the main is the ISP offer IP based on the MAC of lower client (i.e MT6000/B3000).
What we need to do is to configure MT6000/B3000 to DHCP, and contact the ISP and provide the MAC address of the WAN port of MT6000/B3000. I think the ISP will offer the IP to the WAN of MT6000/B3000 via IPOE.
Kindly note, have to select the factory MAC for WAN of MT6000/B3000, do not random or clone.