My ISP ONT has the address 192.168.100.1 on the physical ethernet interface and that interface is connected to one of my physical ethernet router port. To get the public IP from my ISP I need to create this structure:
Router physical ethernet interface
ISP vlan interface
PPPOE interface
and everything is working fine, the PPPOE interface get the public ip and that creates a route to ONT network (192.168.100.1) through the public IP (PPPOE interface gateway).
What I'm trying to do is to connect to the web interface of my ISP ONT with a direct access to its address (192.168.100.1) that's reachable through the router physical interface but I can't do that because there's already a route (the public ip through pppoe) with 192.168.100.0/24 as destination address. If I disable the pppoe interface and give to the router physical ethernet interface the address 192.168.100.2 I can access the web interface but as soon as I re-enable the pppoe it become unreachable