If it’s any use, here are the WAN IPv6 options (auto, manual, or IPv6CP Extension) for the ZTE-ZXHN-F670, it’s set to auto right now:

And these are the available LAN settings:

I’m located in Vietnam; the ISP is Viettel (probably not useful information, but hey, why not).

Is it possible to send the hint from OPNsense itself? I mentioned in the original post that OPNsense is behind the ISP router (ZTE-ZXHN-F670) which I kind of don’t want to touch due to the fact that the terminology is quite different and that the ISP people come over to run tests on it whenever there are service issues. Either way, I’ve already tried to search through the settings and couldn’t find any options for setting the prefix hint on the WAN side. I’m open to digging though those settings again if you’re familiar with the router.

I’ll try this when I get a chance. Off the top of my head, why did you set the prefix to 0x1? I was under the impression that it only needs to be set if there are multiple vlans and what are your rules for the WAN side of the firewall? My LAN interface is only getting an LLA so maybe it’s being blocked from communicating with the ISP router.

I did forget to mention that. The IP addresses of the devices on the LAN do not share the same first half of the address as the IP on the ISP router. I have the OPNsense LAN set to track WAN interface, but the DHCP server is stuck saying “No available address range for configured interface subnet size.”. I also noticed that my WAN for OPNsense has a global routable IP starting with 2402 as well as a LLA starting with fe80 but my LAN only has a LLA.

Which routes and firewall rules should I be checking?

I ultimately did go with Syncthing and uploading my files encrypted to Google Drive for backup. It’s been working great for months. I’ve also been using Zeroteir to make this work with my laptop too while on the go.

Thanks, I’ll look more into it.

Duplicati looks very promising, but from a cursory glance it’s more for backups? Since the files are split into chunks, I would still need to use a NAS or local cloud storage and have Duplicati do the final upload to GDrive.