IPv6 (temporary) broken

I have received a new toy to play with, a Sophos SG125W firewall. And despite being a high-end and expensive networking device, I can’t get my internet connection (XS4ALL) working with IPv6.

XS4ALL is using a VLAN, VLAN 6, for internet access. And they are using PPPoE. Which was also a harsh to get it working because you cannot set a VLAN tag on the WAN port. You can enter a VLAN if you are using a plain simple ethernet connection, but not if you are using an PPPoE connection. If you specify that you are using VDSL you can enter a VLAN, but setting up a VDSL connection isn’t going to work if you are using FttH…

Thus I needed a managed switch, and the VLAN tag is now being stripped before connecting to the Sophos WAN port. Now I can setup a PPPoE connection, but no IPv6 🙁 

The Sophos UTM isn’t getting an IPv6 prefix automatically, while my old OpenWRT router did. And when I enter my /48 range manually, the gateway is some link local address, and my knowledge is lacking some skills to fix it… yet!