I recently switched from my FritzBox to the provider modem and the USG. Unfortunately, I have the problem that my provider uses a CarrierNAT and I cannot see my real external IP on the USG. There is a 100.x.x.x from the provider's network. With the OPENWRT devices, you can tell it to pull the IP address from another source (ping of an Internet page). Is this also possible somehow with the USG? Otherwise, all features such as the site-to-site VPN can only be set up in a roundabout way because a wrong address is always used.
My second problem concerns the DNS. If I enter a different IP (126.96.36.199 or 188.8.131.52) in the WAN connection, after a few minutes I no longer have Internet at the clients. First I solved this by passing the DNS data to the clients via DHCP, but the USG should not use the DNS of the provider. This worked without any problems with the FritzBox. Is the provider blocking this or is this perhaps due to my first problem, that I am working with a "wrong" external Ip address?