1、 Basic troubleshooting of physical connection (give priority to inspection and eliminate visual faults)
Cable inspection
Confirm that standard CAT5e and above unshielded twisted pair cables are used (4 pairs of cables are required for PoE transmission, and only 2 pairs of low-quality cables are available), and the length does not exceed 100 meters (PoE standard transmission distance);
Check whether the crystal heads at both ends of the cable are loose or oxidized. Re plug or replace the spare cable for testing;
Observe whether the cable is damaged or squeezed (such as being crushed by a heavy object), to avoid that the port does not respond due to open circuit/short circuit of the cable.
Port and device status observation
To view the PoE switch port LEDs:
If there is no light: the port is not powered on or the hardware is faulty;
If the light is on but the flicker is abnormal (such as frequent flash/constant flash): it may be a bad cable contact or a problem at the device end;
Check the powered equipment (such as camera, AP): confirm that the power switch of the equipment has been turned on, and the equipment itself has no hardware failure (you can test whether the equipment works normally through an external independent power supply).
2、 PoE power supply special troubleshooting (core troubleshooting points to avoid insufficient power supply/configuration problems)
Confirmation of switch total power and port power supply capability
Log in to the switch web management interface (or through CLI commands) to view the total PoE power surplus:
If the total power has been exhausted (the remaining is 0): the PoE function of other non critical ports needs to be turned off, or a higher power PoE switch needs to be replaced;
Confirm the PoE standard supported by the port (802.3af/802.3at/passive PoE):
If the required power of the powered equipment exceeds the maximum output of the port (for example, the at equipment is connected to the af port), the port will reject power supply (some switches support dynamic power distribution, which needs to be manually enabled).
Port PoE function configuration check
Confirm that the PoE function of the target port is enabled (PoE is turned off by default for some switches and needs to be turned on manually):
Web interface path: "Port Configuration → PoE Configuration → Target Port → Enable PoE";
Check the PoE power supply mode of the port: give priority to "auto negotiation" (let the switch negotiate the power supply standard with the device) to avoid the device incompatibility caused by the forced setting of high power mode.
Port power distribution and abnormal protection troubleshooting
Check whether the port triggers overload/short circuit protection:
If the management interface displays "Port PoE protection triggered": it may be the short circuit of the powered device (such as the failure of the device power module), disconnect the device to test whether the port is restored;
Confirm that the port is not configured with "power limit" (such as manually setting a power value lower than the device demand).
3、 Troubleshooting port configuration and network compatibility (troubleshooting logical layer faults)
Port basic configuration verification
Check whether the port is disabled (Web interface "Port status" or CLI command "show interfaces status"): if "down" is displayed, manually enable the port;
Confirm the port rate/duplex mode: set to "auto negotiation" (to avoid mismatching with the rate of the powered device, for example, the device supports 100M, and the port is forced to 1000M, resulting in communication failure);
Troubleshooting VLAN and port isolation: confirm that the target port has been added to the correct VLAN and is not configured with "port isolation" or "access control list (ACL)" to restrict data transmission.
Compatibility test
Replace the powered device: use a known normal PoE device (such as a standby AP) to access the target port. If the power supply is normal, the original device is incompatible (for example, the device supports passive PoE, and the switch is standard 802.3af);
Cross test port: Connect the equipment that works normally to the target port, and connect the equipment of the faulty port to the normal port to determine whether it is a "port problem" or a "device problem".
4、 Final troubleshooting of hardware and system (troubleshooting of equipment itself)
Switch system and firmware check
Restart the PoE switch: some temporary system failures can be recovered by restarting;
Upgrade switch firmware: The old firmware may have PoE power supply logic vulnerabilities. Download the latest firmware from the manufacturer's official website and upgrade according to the guide (backup the configuration before upgrading).
Hardware fault confirmation
If the above steps are invalid and multiple ports fail at the same time: the PoE power supply module of the switch may be damaged (contact the manufacturer for maintenance);
If only a single port fails: try to restore the factory settings of the switch (backup the configuration in advance). If it still fails, the port hardware is damaged. You need to disable the port and use the standby port.