Start at the ISP handoff
Confirm the modem or ONT port, service tier, and router WAN port. A 2.5Gbps plan connected through a one-gigabit handoff cannot reach the intended speed regardless of the mesh label.
Assign one job to every fast port
Decide whether the fastest port serves WAN, Ethernet backhaul, switch uplink, NAS, or a workstation. Avoid buying a router with one 2.5GbE port when the same port must serve both WAN and the local network.
Count the devices behind the switch
List desktops, NAS, TVs, access points, cameras, and mesh satellites. A compact unmanaged switch can add ports, but every client still negotiates at its own adapter speed and shares the uplink.
Check the client adapter and operating system
A laptop may need a compatible USB-C or USB-A 2.5GbE adapter, current driver, and a suitable dock path. Confirm the host port, cable, driver, and negotiated link rather than trusting the adapter box.
Use the right cable and test the negotiated link
Use a sound Cat5e or better run within the installed path and replace suspect patch cables before replacing the router. Test the link speed, local file transfer, and internet speed separately.