Layer 2 refers to the Data Link layer in the Open Systems Interconnection model. Layer 2 Ethernet switches are network devices that are used inside local area networks to establish Ethernet connection to multiple different devices, such as PCs, printers, surveillance equipment or PLCs. Layer 2 switching operates at MAC address level to forward Ethernet packets based on the MAC address source and MAC address destination data contained in an Ethernet frame. By analyzing this information, an Ethernet switch assigns appropriate ports to be used when forwarding the data to its destination. Ethernet switches can be subdivided into three major categories: unmanaged, fully managed and unmanaged with very basic configuration options. Based on the design, Ethernet switches can be mounted in a few different ways: attached to a DIN-rail, mounted directly to a panel, wall or placed in a 19 inch rack enclosure. They can have a wide range of port counts starting at 2 and going up to 48 or more. Ethernet switches with larger port count are typically used inside the IT server rooms where they are mounted in the 19 inch rack systems. The designer can also differentiate Ethernet switches based on the port types such as regular RJ45 ports, Fiber Optic ports, SFP or more industrial ports such as M12 circular ports. Ethernet switches also support different communication speeds, with 100 Mbit/s being the most common.