An Ethernet switch is a network device that connects multiple Ethernet-capable devices on a local area network and forwards traffic between them. It operates at Layer 2 of the OSI model, learning which device sits on each port by reading source MAC addresses, then forwarding incoming frames only to the port where the destination device lives.

In short: Ethernet switches range from small unmanaged 5-port desk units (where every port is equal and the switch operates with no configuration) to fully managed industrial switches with VLAN segmentation, QoS, ring redundancy, and SNMP monitoring. Industrial Ethernet switches add features needed for OT environments: ruggedised housings, wide temperature operation, DIN rail mounting, redundant DC power inputs, and support for industrial protocols like Profinet, EtherNet/IP, or BACnet.

For IoT deployments, switches are typically used either as expansion behind a cellular router (the router has two or four LAN ports; a downstream switch extends that to eight, sixteen, or twenty-four), or as the core of a small plant network with the router providing only the cellular WAN link. Teltonika's TSW series (TSW101, TSW110, TSW200, TSW210) offers managed switches sized for typical IoT deployments. Larger industrial switches from vendors like Westermo, Moxa, and Hirschmann suit more demanding plant environments.

PoE-capable switches (delivering power to cameras, access points, and IoT devices over the Ethernet cable) have largely become the default specification for CCTV and security deployments, since they remove the need for separate power supplies at each connected device.