I have been working a bit with POE powered devices and POE switches and I wish that the behavior of POE switches when it comes to POE-LLDP was more consistent.
For example, there is one type of switch (HP 1910 for example) that works like this:
- POE-PD device asks for 25.5W from a 25.5W (802.3at) POE PSE switch.
- POE-PSE gives 12.95W to the POE-PD.
- POE-PD connects to POE-PSE LLDP and sees that the device can provide 25.5W, but it shows that the "PD Requested" field is 0.0W and "PSE Allocated" is 0.0W.
- POE-PD asks for 25.5W in LLDP (in "PD Requested" field).
- After handshake the POE-PSE reports "PD Requested" field is 25.5W and "PSE Allocated" is 25.5W (which is OK).
Another type of switch (from Rubytech) do the following
- POE-PD device asks for 25.5W in HW negotiation.
- POE-PSE allocates 25.5W to POE-PD in HW neg.
- POE-PD starts LLDP to check if it can negotiate down the power.
- POE-PSE reports "PD Requested" field is 25.5W and "PSE Allocated" is 0.0W.
- Even after multiple handshakes, the above values stays (allocated=0.0W). The PSE refuses to tell the PD how much it has allocated in LLDP.
I would prefer if the values shown in LLDP POE-PSE reports "PD Requested" and "PSE Allocated" fields matched what the hardware negotiation has resulted in.
It would also make it easier to detect the case where a POE injector is connected between a POE-switch and a POE-PD device.
Are there any specifications or guidelines that ask POE switch manufacturers to handle these things (LLDP) consistently?