How to Fix Cisco 9300 All PoE Ports Go Out for 1 Second?

Are you facing a frustrating issue where all PoE ports on your Cisco 9300 go down for 1 second? Devices like IP phones, wireless access points, or security cameras may suddenly lose power—only to restore themselves moments later.

This short but system-wide power outage is not a single-port issue. It points to a deeper failure within the PoE subsystem and should be addressed to prevent further network instability. This guide will walk you through the causes and solutions.

Why Do All PoE Ports Drop Simultaneously?

Yes, the Cisco Catalyst 9300 series supports PoE, PoE+, UPOE, and even UPOE+, depending on model. But if every PoE port goes out, consider the following root causes:

1. Power Supply System Issues

• External Power Instability: Power surges or sags in the building supply can trigger internal protection, causing PoE to reset.
• Overheating PSU: Look for log entries like %ILPOWER-3-CONTROLLER_PORT_ERR: Power Supply Over Heat.
• Power Budget Exceeded: If total device draw exceeds available PoE capacity, the switch may reset PoE output to protect itself.
• Failing PSU Module: Intermittent hardware degradation in the internal or external power supply can cause symptoms like this.

2. Software Bugs or Misconfiguration

• IOS XE Bugs: Known issues in versions like IOS XE 17.6.4 or specific 9300L models (see Bug IDs CSCwe22958, CSCwe54104, CSCvs52594) can disrupt PoE control functions.
• PoE Controller POST Failure: A failed power-on self-test will disable PoE globally.

Step-by-Step Troubleshooting Guide (With CLI Commands)

Step 1: Run Diagnostics & Analyze Logs

• Check System Logs

show logging

Look for any %ILPOWER, %SYS, or %PLATFORM messages around the time of failure.

• Verify Power Supply Health & Budget

show environment power
show power inline

Ensure PSU is "OK" and PoE Available Wattage > Used Wattage. If it's close or exceeded, you may need a higher-capacity PSU.

• Confirm POST Results

show post

Look for PoE Controller and make sure it shows "Passed."

Step 2: Take Action

Cold Reboot (Full Power Cycle)

Disconnect all power cables from the switch (and stack members, if any), wait 30 seconds, then reconnect. This clears transient power state faults without affecting config.

Upgrade IOS XE

If running a version with known PoE bugs, update to a Cisco-recommended stable release. This is often the most effective long-term solution.

Expand Power Capacity

If the PoE load is consistently exceeding your budget, you have several options:

• Reduce attached devices or manage their power draw using commands detailed in Cisco's official PoE Configuration Guide.
• Add redundancy with a secondary power supply, an option explained in the Catalyst 9300 Data Sheet.
• Upgrade to a higher-wattage model.

Pro Tip:

Always maintain a 15–20% buffer in your PoE power budget to avoid unexpected resets when devices draw peak power during boot or reconnection.

Your Next Steps

If these steps resolve your issue, that's great news. However, if the problem persists, it could indicate a more serious hardware issue with the switch itself.

In that case, it may be time to consider a replacement. You can explore our full range of Cisco Catalyst 9300 Series to find a model that fits your needs and budget. For any questions, our team of experts is always ready to help.