Kerans:

 

Definitely in the Fibre port, not one of the ethernet ports. The internet is speedy and consistent when connecting directly to the ethernet.

 

The old router is a NetGear AC750 R6020, which in theory can support 300 - 400 mbps... but I'm hesitant to reset it and access the settings in case I need credentials I don't have to get the internet back up and running. The landlords are great, just trying not to bother them if I can fix it myself.