Network switches provide a physical connection between two devices on a network segment. They allow computers to communicate directly with each other without having to pass through a router. A single computer may have several network cards, which are connected to different networks. The computer needs a way to determine which network it should send information to and receive information from. This is where a switch comes into play. It allows the computer to choose which network card to route its traffic to and receive traffic from.

Once a device is connected to the Switch, the Switch notes the media access control (MAC) address, a code that is baked into the network interface card (NIC) that attaches to an ethernet cable that attaches to the Switch. The Switch uses the Mac address to identify which attached devices are sending out packets and where to deliver the incoming packet. So the MAC address is used to identify the physical device and not the Layer 3 IP address, which can be assigned dynamically.

A full-duplex means you can talk to someone while sending them something else. A switch does this by reading the headers of incoming packets and matching them to outgoing packets. This makes sure there aren’t any collisions when both devices are trying to send data at the same time.

Switches operate at layer three. VLANs are used to connect different networks together. Routing allows traffic to be sent from one subnet to the other.

More info: What is a network switch