Hi Tulpenkicker,
Today morning I made the mistake to connect the port 1 of Zyxel3006-D70A to the router, this cannot work, because it is console only. After connecting to Port 4 and re-initializing the network it worked again.
The old Zyxel modem VMG1312 had no specific console port.
As Arne posted the Munich Provider M-Net uses VLAN 40. I will try this tomorrow.
“Zuführung in die Whg. über VDSL2 gemäß ITU-T G.993.2 mit VLAN Tagging gemäß IEEE 802.1Q (VLAN 40)”
And about the update - yes I know … but it was very much work the last weeks and we are three here working in home-office / home-schooling … never touch a running system 
I will upgrade soon.
Best Regards
Wolfram