I needed a small tweak to my EdgeRouter config to let me connect to my bridged VDSL modem. The EdgeRouter is connected to the modem on eth0.
The modem uses
192.168.1.254/24 by default, so the first step is to give eth0 an IP on the same network. Then we need a NAT masquerade rule to NAT traffic for the
192.168.1.0/24 network through eth0.
After applying the changes I can now browse to the admin interface of the modem.