Favour: anyone in Dunedin with a UniFi PoE switch?

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mjb

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#303810 10-Mar-2023 14:16

For a proof of concept I need to check if a device powers up correctly with a crossover cable. I have the device, two short test cables, and can come to you.

I unfortunately just sold my UniFi PoE switch...

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nicmair

244 posts

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#3048672 10-Mar-2023 15:07

does it need to be unfi swich, I have lots of PoE switches you could test against (mostly Huawei), or I have official ubiquity PoE injectors if that would help.

(and I'm based here in Dunedin)

CYaBro

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#3048676 10-Mar-2023 15:16

I’m in Oamaru if you want to go for a drive? :)

Opinions are my own and not the views of my employer.

lxsw20

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#3048678 10-Mar-2023 15:20

Yeah I've got an 8 Port in Dunedin if you want to test. You break it you buy it ;)

Oh yeah are you looking for something with Unifis weird 24v PoE or proper 48v poe? I've just got a switch that does the latter.

toejam316

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#3048684 10-Mar-2023 15:38

Are you talking about a full cross-over or standard cross-over cable? standard crossover leaves pins 4,5,7 and 8 alone, which are the power pins for 24V passive PoE for UBNT devices, full crossover (unlikely) has those crossed too which could give negative voltage, probably not ideal.

I believe a crossover cable is also fine for 802.3 AF/AT, but don't quote me on that one.

The next question would be, why? You could reterminate the cable, or purchase/create an adapter to uncross the cable. Straight T568B is the best way in all instances, IMO.

Anything I say is the ramblings of an ill informed, opinionated so-and-so, and not representative of any of my past, present or future employers, and is also probably best disregarded.

mjb

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#3048701 10-Mar-2023 16:11

toejam316:

Are you talking about a full cross-over or standard cross-over cable? standard crossover leaves pins 4,5,7 and 8 alone, which are the power pins for 24V passive PoE for UBNT devices, full crossover (unlikely) has those crossed too which could give negative voltage, probably not ideal.

I believe a crossover cable is also fine for 802.3 AF/AT, but don't quote me on that one.

The next question would be, why? You could reterminate the cable, or purchase/create an adapter to uncross the cable. Straight T568B is the best way in all instances, IMO.

The device in question (Mikrotik mAP Lite) has inverted power pins, I have no idea why... it just does. hence the need to test that it powers up with a crossover cable. (T568B crossover, not rolled (cisco console/yost serial standard))

As with all things, it's not as simple as 4,5,7,8. This reddit thread has a good explanation. Looks like a crossover will do what I need, I just need to verify before money is spent.

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mjb

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#3048749 10-Mar-2023 16:13

lxsw20:

Yeah I've got an 8 Port in Dunedin if you want to test. You break it you buy it ;)

Oh yeah are you looking for something with Unifis weird 24v PoE or proper 48v poe? I've just got a switch that does the latter.

It needs to be a UniFi switch, as that's where the device (well, several of them) will be deployed.

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mjb

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#3048752 10-Mar-2023 16:17

lxsw20:

Yeah I've got an 8 Port in Dunedin if you want to test. You break it you buy it ;)

Oh... and yes, that would be awesome - have a friend that responded to a txt after I posted the thread that may let me test as I swing past this evening. will get back to you if that doesn't pan out.

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lxsw20

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#3048753 10-Mar-2023 16:18

It's a US-8-60W - is the device you're using 802.11af? If so that should be fine.

toejam316

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#3048762 10-Mar-2023 16:26

Well I've learned of a new weird limitation of a cheap Mikrotik device. I do worry for you, having a situation where you need to deploy mAP lite's though, sounds horrendous.

Anything I say is the ramblings of an ill informed, opinionated so-and-so, and not representative of any of my past, present or future employers, and is also probably best disregarded.

mjb

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#3048776 10-Mar-2023 16:42

toejam316:

Well I've learned of a new weird limitation of a cheap Mikrotik device. I do worry for you, having a situation where you need to deploy mAP lite's though, sounds horrendous.

Hah, they're actually perfect. small, PoE capable, and able to be scripted to do stuff.

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