4.1Status lights and ports

When you arrive at a network fault, the first clue is not a screen but the lights (LEDs) on the front of the device. Whether a cable is properly connected and whether traffic is flowing can largely be read from the color and solid/blinking state of a link light alone. Also, sockets that look alike differ entirely in role—the console port for configuration, the Ethernet port for traffic, the SFP for optical fiber—and plugging into the wrong one will not work. This section teaches how to read the lights and the role of each port, as the introductory basics of judging state by eye and choosing the right socket.

4.1.1Link light (LED) colors and states

• Off means no link on that port—suspect an unplugged or broken cable, or the far end powered off. It is the most basic sign of "is it physically connected."
• Solid green means link up—physically connected to the far end. Blinking green signals traffic is flowing, flickering as data is sent and received. So read "solid = connected" and "blinking = communicating."
• Orange/amber indicates, depending on model, a warning, error, or a particular speed or state (e.g., a speed mismatch, a disabled port, or signs of a fault). The exact meaning should be confirmed in the model's manual, but the rough frame "green = normal, amber = needs checking" gives a first guess.