Well, it's a one armed router. Port 5 is uplink to NUC, port 2 is lan and port 4 is wan. LAN is a VLAN, WAN is another VLAN, uplink is tagged for both. Standard setup, nothing strange.
The thing is, this setup works in my network if I connect the WAN (port 4 of the switch in the one armed setup) to the existing network (LAN side) on DHCP. I have internet while I'm connected behind the one armed router. Port forwarding works as well.
But when I take the wan cable out of the existing setup and put it into my one armed router (wan port on the switch, port 4), I can only access the LAN side of the network, I can access the pfsense webpage, DHCP works, but no internet.
Also, I tried to power cycle all the other gear, I cloned the MAC of the existing router, still nothing (existing router is not cloning any other MAC, I checked that as well). I checked many times, WAN settings are correct.
How do I troubleshoot this? I'll call the internet provider tomorrow, maybe they have some ideas.