Wired Intelligent Edge (Campus Switching and Routing)

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Aruba Employee

POE Problems

Scenario

I spent a long time onsite today working through some messy POE/POE+ issues. The problem statement in a nutshell "2930M switch does not power camera".

 

The camera doesn't actually have a POE/POE+ input port, but instead has an ethernet port and 12V connector. An additional external box splits the POE+ connection from the switch into data (ethernet) and a separate power feed.

 

Symptoms

  • Directly connecting the power splitter + camera to the 2930M POE+ port didn't power on the camera without configuration changes (see "Useful Commands" below).
  • port would sometimes flap - power on/power off
  • switch logfile indicated several POE related errors
  • additional problems seemed to arise when three or mode cameras were connected
  • multiple switch brands and models experienced similar or identical symptoms

Sample logfile entries

 

W 07/25/18 13:54:39 00564 ports: port 5 PD Invalid Signature indication.
W 07/25/18 13:54:37 00562 ports: port 5 PD Over Current indication.
I 07/25/18 13:54:37 00077 ports: port 5 is now off-line
I 07/25/18 13:54:36 00565 ports: port 5 PD Removed.
W 07/25/18 13:54:36 00562 ports: port 5 PD Over Current indication.

 Example of excess power draw

5     Yes  critical on      value value  30.0 W  31.8 W  Delivering   4   2
6     Yes  critical on      value value  30.0 W  18.4 W  Delivering   4   2

 

Answer

In fact the 2930M switch is fully compliant with 802.3at - POE+, with support for a maximum of 30W. On several occasions, the switch reported 31.8W on the port - and shut down. This is exactly what it is supposed to do.

 

Even though the splitter specified 802.3at POE+ compliance, that seemed doubtful. The switch log entries were conclusive in pointing to a non-compliant endpoint.

 

External third-party POE injectors that supplied 35W have been used as the fallback solution.

 

Useful Commands

The interface has some POE options; these ones helped:

poe-allocate-by value
poe-value 30

In addition, this command run at the global level (ie not from the interface perspective) alloed the camera to power on:

power-over-ethernet pre-std-detect ports <port IDs>

Both should be used with caution.



Richard Litchfield, HPE Aruba
Network Solution Architect
Network Ambassador
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