Although some newer network devices are marketed as "Layer 3 switches," traditional switches operate at the Data Link layer.
A "gateway" is a generic term for an internetworking system that can be implemented completely in software, completely in hardware, or as a combination of the two. Depending on its implementation, a gateway can operate at literally any level of OSI. Most run at an Application layer or Network layer
Routers, on the other hand, are true Layer 3 devices. Routers address and communicate with each other through a specific network layer protocol such as IP.
