1.Since it is OK under bridge mode, it means the config of BRAS is OK, problem should be on the OLT or ONT.
2.Set the ONT as Router and Bridge mode separately, and capure the trace on the uplink of OLT. Under bridge mode, PADI packet is captured; but under Router mode, there is no any PADI packet, it means HG850a did not send the PADI packet under Router mode, which casued PPPoE can not establish.
3.Check the config file of OLT and HG850a, no fault is found. For further analysis, check the HG850a WAN status by the OLT internal channel:
576 root 416 S dhcpc -i wan0 -I wan0
577 root 416 S dhcpc -i wan0 -I wan0
757 root 616 S dhcps
There is only one DHCP WAN, but no PPPoE WAN, but on the WEB interface we can see there are 2 WAN: one is DHCP, the other is PPPoE WAN.
4. It is very strange, we dicided to check the XML file more carefully, and found the two WAN ports were using the same WAN ID, both are "1" :
On the BMS, we can see that more clearly:
As the second WAN ID the same as the first one, the second WAN port(PPPoE) can not start. As a result, PPPoE can not be established.
5. Change the XML manually, to make the WAN ID different. After that, PPPoE can be established under Router mode too.
6. But problem can not be closed here, need to know how can the 2 WAN ports get the same WAN ID. Customer did not set it, and there is no where to set the WAN ID on ONT, OLT or BMS.
7. Take a review of the customer's service-providing process, find that cusotmer bind one VAS profile to generate the XML file, the VAS profile is from other BMS, did not match the customer's BMS, can not understand all the HG850a nodes, and the same 2 WAN ID appears.
8. Till now the problem is clear and located, VAS profile mismatch BMS, lead to the same 2 WAN ID, and then lead to the second WAN can not be started, and cause the PPPoE can not be established.
So, the final solution is to create one VAS profile on BMS manually, the parameter can be the same as before, and then bind the new VAS profile to the ONT, problem can be solved.
PS. You can find the following in the attachment: configrations of OLT and ONT, network scheme, trace of OLT uplink.