Hi everyone,

I'm trying to see if I can properly set up the router with my ISP. I didn't want to get to ISP specifics but it seems it's unavoidable.

This is regarding using the BE900 with Softbank in Japan. I've found one more thread about this which seems to have it resolved, however I couldn't make it work on my end:

https://community.tp-link.com/en/home/forum/topic/715152

TP-Link also has an article about Japanese ISPs here (in Japanese):
https://www.tp-link.com/jp/support/faq/10/

Essentially, Softbank seems to have their proprietary system to create IPv4 over IPv6, they call IPv6(IPoE/IPv4 over IPv6). As far as I could understand this is the v6plus. They say you can't get IPv6 with your own router unless you connect it to their router. They provide a modem and a router.
TP-Link's article says to connect the router to the Softbank router and set it to Access Point mode, but maybe this was written before they supported v6plus.

I have tried the following:

A. Connecting BE900 directly to the modem:

1. Using v6plus doesn't have an option for credentials with username/password. It seems to connect to IPv6 but I don't get an IPv4. Some websites like youtube work, while most websites don't work.

2. Using PPPoE does have option for credentials and I get an IPv4. For IPv6, if I use Dynamic IP I sometimes get an IP but seems unstable. If I enable Prefix Delegation then it doesn't work.

B. Connecting BE900 to the Softbank Router (BBUnit)
1. I tried using it as a second router but didn't get any better results. v6plus doesn't work at all. PPPoE works as before.
2. I tried using it as an access point, but then I lose all router functionality such a VPN Clients. Furthermore, I can no longer connect to my NAS which is connected to the BE900.

C. What I'm using now:
I am using the BE900 directly connected to the modem, with PPPoE and I disabled IPv6. This seems a stable but not ideal solution.

Is there any way I can improve this and properly set up IPv6?
Should the v6plus "just work"? Or maybe it is still missing an important functionality such as a way to input credentials?