If you have a managed 2.5Gbps switch with two free ports, I would set an (untagged) VLAN for your WAN connection. It sounds like the modem is not very good at speed negotiation. That is after you've ruled out your cable, of course. Bart...
Isn't this possible in the media settings of the interface?Cheers,Franco
You need to assign the parent of the VLAN in order to adjust its media settings.Cheers,Franco
I'm guessing that the modem does not do autonegotiation very well https://en.wikipedia.org/wiki/AutonegotiationYou may need to hang a scope on a breakout of the wires to be sure, but as you said - diminishing returns if you only bounce the firewall once a month.