The EX Series and QFX Series are designed for different parts of the network, though both run Junos OS. The EX Series is Juniper's campus and enterprise switching family, optimised for access-layer and aggregation deployments where PoE, user device connectivity, and Virtual Chassis stacking are priorities. EX Series switches scale from 1GbE access ports up to 100GbE uplinks depending on the model. The QFX Series is Juniper's data centre switching family, optimised for top-of-rack server and storage connectivity, spine-and-leaf fabrics, and high-throughput environments. QFX switches support advanced data centre protocols including VXLAN and EVPN for software-defined networking overlays, and are available with port speeds from 10GbE through to 400GbE. Many organisations deploy both families within the same network, using EX switches for campus access and aggregation roles while QFX switches power the data centre fabric. As a general guide: if you are networking end users, phones, and access points, EX is the right family; if you are networking servers, storage, and building data centre fabrics, QFX is the right choice.