(AC 2000 : R6850) not working with PPoE connection (Working as DHCP Client )

[Ketan_Patel]

I have purchased R6850 AC2000 model after 5-6 months it stopperd working (issue some time internt connect and drop frequently no issue from ISP). so i replaced it replacement had same issue with PPoE it didnt respond to provider side so mac id could not set. second time i replaced it now i am facing same issue with third one,ISP provider tech guy exercised for 3 hours but not solved the problem. it is working as DHCP Client but not wroking with PPoE. if any one know the any setting regarding this issue please post me 

[plemans]

what modem/gateway is it connected to? 

Not all isp supplied gateways function properly in passthrough mode.