Field Guide · hardware

Also known as: Ethernet switch, switch

A network switch is a device that connects multiple machines on the same local network, forwarding each Ethernet frame only out the port that leads to its destination.1

host A host B host Cdest MAC host D switch MAC → port table frame for C no flood forwarded to the one matching port — a hub copies it to all
A switch learns which MAC sits on each port, so a frame goes only out the port for its destination — here just host C, while B and D stay idle. An older hub had no table and copied every frame to every port; that switched forwarding is why modern wired LANs are fast and quiet.

Overview

A switch learns which MAC address lives on which port and builds a forwarding table, so traffic between two hosts does not flood every other port — this is what makes a modern wired LAN fast and quiet compared with the old shared hubs. Switches range from cheap unmanaged boxes with a handful of ports to managed units offering VLANs, monitoring, and Power over Ethernet. A switch works within one network; moving traffic between networks is the job of a router.

Where it fits

The switch is the wiring hub of a wired LAN, where each device’s NIC plugs in. For a GopherTrunk site with several wired nodes — capture boxes, a storage server, a workstation — a small switch ties them together, and a PoE switch can even power a Raspberry Pi node over the same cable.

Sources

  1. Network switch — Wikipedia, on the device that forwards frames within a local network. ↩

See also