I recently installed a hEX at a client who had 802.3af PoE on their WAN Ethernet link. According to the spec sheet of the RB750Gr3, only passive PoE is supported, so imagine my surprise when I plugged the WAN cable to Ether1 and the hEX powered up…
Is this a safe configuration? The supported passive PoE is only 8-30 V and 802.3af would be 48V. Presumably if the device negotiated 802.3af it would be safe to use, but I want to confirm this before the device burns up randomly.
What is the “/system health print” output on RB750Gr3 (hEX)?
I ended up disconnecting the hEX and used a hAP AC2 instead so I unfortunately can’t check that. I don’t believe the hAP AC2 powered on from the cable but now I am wondering if perhaps I missed it.
I can’t say for certain that the other end of the link was 802.3af compliant, the previous device which I was replacing was an 802.3af access point but after looking it up and checking the specs, it also supported passive PoE. The client was also frequently connecting this cable directly to their PC, which with passive PoE would likely result in damage, but the PC Ethernet worked fine.
Normally on most PoE switches/routers of different brands, the default configuration of PoE is “Auto”, means that the PoE device first detect if the other device needs powering though Ethernet. So, is secure use PoE devices with any Ethernet device.
Regards.
“Real” (802.3af) PoE can be automatic or forced-on, passive PoE as used by Mikrotik supplies the power constantly with no negotiation, so you can fry things that aren’t expecting it.
That is not true.
Mikrotik’s passive PoE in fact also checks if the other side accepts power before turning it on.
Not sure about injectors, but 100% for switches, etc.
Injectors certainly can’t perform any negotiation, they are dumb devices which just put power onto the cable. There is some kind of proprietary negotiation with passive PoE out on Mikrotik switches, but as I don’t know what is on the other end of this cable I have to assume it was an injector or 802.3af PoE, I certainly don’t expect it to be a Mikrotik switch.
I have a PowerBox Pro and all my devices are powered by Passive PoE. I connect 2 PC’s and the negotiation is a bit slower than a regular MikroTik switch because it checks PoE function first.
PoE is very simple, work or not work, it never will try to force incorrect powering to a device. This technology was created to be safe.
Injectors also checks powering. One time I put 48v PoE to 12v CCTV camera. Next day I put correct PoE and all worked OK, nothing was “fried”.
I never saw a broken Ethernet computer port by a PoE port that “fries” it. If PoE is so unsecure, by normative never we can connect any computer to any PoE switch, but, we no have problems with this.
Regards.