I am soon going to set up something similar to this setup/combo, however I am going to use a Zyxel VMG3925-B10B as the modem in bridge mode (NAT, Firewall & DHCP disabled) instead, and the 7530 as the OpenWrt router & AP (NOT just a dumb AP).
@slh , we had a conversation about a similar combo almost 2 years ago here, that time with the Zyxel + a BT HH 5A. I bought the R7800 as discussed (soon after, I decommissioned the Zyxel too because I moved to a home that offered FTTH), and set up the Zyxel + BT HH5A combo to my father's home, which works till now.
I want to replace the BT HH5A in my father's home with a spare FB 7530 with OpenWrt for various reasons, but mainly because it has a newer processor and I trust the overall performance would be better.
Where I am with FB 7530 at the moment is here (the default OpenWrt setup):
Similar to the previous setup, I trust that I need to create a new WAN interface with PPPoE protocol (and DHCP server enabled ?) and link it to the relevant VLAN ID (eth0.xx). However I struggle to define what the new VLAN should be, because FB 7530 does not have a dedicated WAN port but 4 LAN ports instead. I understand that a VLAN ID should "simulate" the hypothetical WAN port via assigning a LAN port.
I have read the below in the ToH VLAN Setup for FB 7530, but I am unsure what to do next.
For sure I do not need the Guest network, so I will delete the 2nd VLAN ID and untag LAN4. I will also avoid ID 1 as suggested with sth else (e.g. 42). But how am I supposed to set the desired VLAN for the "simulated" WAN port?
The added difficulty (for me at least) is that I have to do this on a plug-and-play basis (ie prepare everything in advance if possible), because I won't have much time available for experiments in my father's home..