Things learned about Ubiquiti PoE adapters and devices

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I posted this a few weeks back to the AgTalk forum.  I thought some might  
find my tale interesting.


Back in September 2009 I set up a 1.5 mile link between farmsteads using  
a pair of Ubiquiti NanoStation 5 Loco units (5 GHz WiFi--802.11a band).  
These proved very reliable through storms and power outages over the  
years until June 30, 2018 when the AP unit at this farmstead went dead  
almost with no reason, i.e. there had not been a recent nearby lightning  
strike, though a squall line had moved through a few hours before with  
some hail. Efforts to access the unit were unsuccessful that evening. The  
decision was made to climb the tower and replace the unit the next day  
which I did. The unit I replaced it with was in service on this farmstead  
for a short link and could be borrowed (the link was down anyway with the  
AP down). The replacement went smoothly and the replacement unit operated  
as the AP without issue. The old AP was reconfigured and put back in  
service for the link where the borrowed unit came from.

All was well until the afternoon of December 28, 2018 when the AP went  
down. I was able to access it on its factory default address and found  
that all settings had been reset to factory defaults. I uploaded the  
previously saved configuration and the unit ran normally for a couple of  
hours and then quit again. Efforts to access it were unsuccessful. The  
next morning, Dec 29, a Saturday, I was able to access it at the factory  
default address and rather than just upload the configuration again, I  
opted to update it to the latest firmware for the older NS5L which is  
AirOS 4.04. All went well for two days before it failed again and this  
time all efforts to access it over the network link failed.

After the failure in June I had ordered a pair of 5 GHz panel antennas  
with the intent of eventually replacing the NS5L at each end with Ubiquiti  
Bullet 5 units so the radio hardware could be accessed from ground level.  
I had failed to order the coaxial cable for this end, however. Rather  
than being able to climb the tower immediately I awaited the arrival of  
50 feet of LMR-400 cable terminated with N male connectors along with a  
PolyPhaser lightning arrestor, both ordered from Amazon on New Years Day.  
Both arrived on Saturday January 5, 2019 which was ideal since there was  
barely any wind and the high temperature hit 62F! The climb was completed  
with the NS5L removed and the panel antenna and coaxial cable installed  
with a single climb to the top.

At the bottom I connected the Bullet and it immediately went into  
firmware upload mode which caused a reset of the configuration to factory  
defaults. I went back and forth on this several times until some Web  
searching revealed that Ubiquiti incorporated a remote reset capability  
into their units but never documented it until the M units were released  
when, with AirOS 5, a setting was available to disable the remote reset.  
From what I found if voltage or ground (I don't recall which) is present  
on the data lines (pins 1,2,3 or 6 on the 8P8C connector), the unit will  
go into remote firmware upload mode. I swapped out the PoE injector with  
a known good one and the problem persisted which pointed to the cabling  
between the house and the Bullet.

The cable had been in place since the initial installation in 2009 and  
was run of the mill UTP (Unshielded Twisted Pair) Cat 5 cable with a  
black outer jacket. In the process of troubleshooting the Bullet I cut  
off the section that ran up the tower and terminated it with a new 8P8C  
connector that did not resolve the issue. As i have a box of Ubiquiti  
Tough Cable which is STP (Shielded Twisted Pair) Cat 5e the only choice  
was to replace the end between the PoE and the Bullet on Sunday which I  
did. Service was restored and has been solid since. I also replaced the  
aging Cat 5 UTP going to the WISP's Nanobeam that had supported three  
generations of their equipment and had a poor splice in it. A nice result  
of doing that for both links was that noise to my amateur radio station  
was greatly reduced and Ubiquiti equipment resets from my transmissions  
were also eliminated. A win win!

Thinking about it after things were working, even had I known about the  
remote firmware upload capability, it would not have mattered as the  
failure state was putting the unit into remote firmware upload  
continuously. I had tried the TFTP method to upload new firmware while  
the NS5L was in failure mode and could not successfully upload any  
firmware. Perhaps the older units did not fully implement the protocol. I  
later removed all the old cabling and didn't find any obvious damage.  
Perhaps the cabling just became contaminated over time. No water seeped  
out that I could tell.

To garner sparing I purchased 2 NOS Bullet M5 units and ordered what I  
thought were the correct PoE adapters for them. Turns out I missed the  
section on the PoE datasheet where it was shown that the ones I ordered  
put power on all four pairs while the units only accept power on 2 pairs--
pins 4,5,7 & 8. At least I was able to order the correct PoE adapters and  
return the incorrect ones for a refund (minus the shipping charge to send  
them back, a bit of stupid tax, I guess). Lesson learned, be careful to  
be sure the PoE and the powered device match though this information  
requires some careful reading to get right.

A bit more work remains as I plan to dig in a conduit to run the network  
cabling in between the tower and the entry point into the basement. That  
will wait until warmer weather!

- Nate

--  

"The optimist proclaims that we live in the best of all
possible worlds.  The pessimist fears this is true."

Web: http://www.n0nb.us GPG key: D55A8819  GitHub: N0NB

Re: Things learned about Ubiquiti PoE adapters and devices
On 2/17/2019 11:58 AM, Nate Bargmann wrote:
Quoted text here. Click to load it

Sounds like good solid troubleshoot skills win again... ;)


Re: Things learned about Ubiquiti PoE adapters and devices
On Sun, 17 Feb 2019 13:15:23 -0600, GlowingBlueMist wrote:

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I wish!

It was more like, "Welp, this is the last thing to try..."

- Nate

--  

"The optimist proclaims that we live in the best of all
possible worlds.  The pessimist fears this is true."

Web: http://www.n0nb.us GPG key: D55A8819  GitHub: N0NB

Re: Things learned about Ubiquiti PoE adapters and devices
On 2/17/19 9:58 AM, Nate Bargmann wrote:
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Ubiquiti supports passive POE which should NOT send any voltage down any  
pairs until the POE brick determines the device attached with accept it.

Generally when a Ubiquiti device starts resetting to defaults it's  
because the voltage pairs are shorting together.. In fact that's how the  
reset button works... Short the pairs for a few seconds (15-20) and the  
device resets to factory defaults..

In the field a crushed or cut cable can exhibit this problem..



Re: Things learned about Ubiquiti PoE adapters and devices
On Mon, 18 Feb 2019 17:22:15 -0800, Johann Beretta wrote:

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The erroneously purchased four-pair PoE bricks did just that, and did not  
supply power to the older device.  It just went to flashing its LED.  
Posting a question on the Ubiquiti forum gave me the answer.

Quoted text here. Click to load it

I didn't find any physical damage where I looked but once the decision  
was made to replace it I didn't inspect it closely at all.  At least if  
presented with a similar situation in the future I'll be better prepared.

- Nate

--  

"The optimist proclaims that we live in the best of all
possible worlds.  The pessimist fears this is true."

Web: http://www.n0nb.us GPG key: D55A8819  GitHub: N0NB

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