[Sjoram]

Agree with the above w.r.t. if the Vigor 130 is working then leave well alone if you're still struggling with it. The only need you might have to access it is to view the connection stats if you suspect a fault on the line. In that case you can do so by connecting a laptop directly to the Vigor 130 with the rest of your network disconnected.

P.S. Your comment regards DHCP server on the Vigor 130 - that is providing the address to the WAN interface of your USG to allow the two to talk to each other and has no bearing on your network behind your USG, so I would leave that alone too.