Hi everybody,
I have a strange problem with RB951Ui-2HnD, and its PoE-in port.
It works (in general) and powers the router properly. The problem arises after power-off, or even reboot - the device does not start when connected only to PoE-enabled enthernet cable. I have to plug-in standard DC, start the router, and after that - the DC plug can be unplugged,as the device still works, taking power from the PoE ethernet.
I would be grateful for any ideas.
What exactly are the symptoms? Device doesn’t show any signs of life? Or device starts to do something but never boots up properly?
If the later: devices often draw more power at boot time than later when operating normally. Inadequate power source might not be able to provide power needed for booting but could provide power for regular operations.
And how exactly does the power setup look like? Do you use PoE switch or power injector?
What exactly are the symptoms? Device doesn’t show any signs of life? Or device starts to do something but never boots up properly?
Yes, it is powered off, until DC connected, then (after proper boot) I can pull the DC plug off and the RB will still work.
And how exactly does the power setup look like? Do you use PoE switch or power injector?
PoE switch, 15 watts per port - maybe it is not enough for RB951 to start?
RB951Ui is rated for input voltage 10V-28V and “passive PoE” … So if your switch is 802.3 af (that’s consistent with 15W power output), then it is using 48V and has potential to fry your RB951Ui. If your switch is not 802.3 af, then state the model (or PoE specs) so we can assess where the problem might be.
RB951Ui rated consumption is 5W, so this should not be a problem.
I’ve tried another configuration - had connected the RB951 to the RB2011 (it has one port capable of PoE, and obviosusly does NOT have 15W per port 
but the symptoms are identical: the RB951 is swithched off until connected to DC, then, after boot, works flawlessly on the PoE…
The test with RB2011 almost definitely proves that there’s something weird going on with your RB951Ui …