How does a network switch work?

Once a device is connected to a switch, the switch notes its media access control (MAC) address, a code that’s baked into the device’s network-interface card (NIC).The NIC attaches to an Ethernet cable that connects to the switch. The switch uses the MAC address to identify which device’s outgoing packets are being sent, and where to deliver incoming packets. The MAC address identifies the physical device and doesn’t change, while the network layer (Layer 3) IP address, can be assigned dynamically to a device and change over time. (Think of a MAC address as the VIN number on a car, and the IP address as the license plate.) When a packet enters the switch, the switch reads its header, then matches the destination address or addresses and sends the packet out through the appropriate ports that lead to the destination devices. To reduce the chance for collisions between network traffic going to and from a switch and a connected device at the same time, most switches offer full-duplex functionality in which packets coming from and going to a device have access to the full bandwidth of the switch connection. (Picture two people talking on smartphones as opposed to a walkie-talkie). While it’s true that switches operate at Layer 2, they can also operate at Layer 3, which is necessary for them to support virtual LANs (VLANs), logical network segments that can span subnets. In order for traffic to get from one subnet to another it must pass between switches, and this is facilitated by routing capabilities built into the switches.