Sometimes, you might find that only the power light is lit on your unmanaged switch when a DUT (device under test like a computer or a router) is connected to the switch, this problem might be caused by non-standard cable, the speed negotiation failure between the. Sometimes, you might find that only the power light is lit on your unmanaged switch when a DUT (device under test like a computer or a router) is connected to the switch, this problem might be caused by non-standard cable, the speed negotiation failure between the. In a basic PoE power supply system, the major components are the power sourcing equipment (PSE), the powered device (PD), and the PoE cables. However, when PoE fails, it can disable critical infrastructure like IP phones, wireless access points, and security cameras. This guide provides a step-by-step troubleshooting. The lights on POE switches mainly include power indicator lights, system operation status lights, POE mode status lights, and business interface indicator lights. Their meanings are as follows: Power indicator light (PWR): Green constantly on: indicates that the power supply of the switch is normal. Understanding the lights on your network or Ethernet ports is essential for maintaining a stable and reliable network. For enterprise IT teams and engineers using Router-switch devices, these LEDs are often the first indicator of network health. This guide explains what each light means, how to.