WS-C3850-24XU PHY Loopback: loopback Test : End, Status Failed

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02-09-2020 06:07 PM
Hi All,
We have a WS-C3850-24XU failed on PHY Loopback: loopback Test.
The switch is stand anlone and is not connect to network.
I run the command : diagnostic start switch 1 test all.
After the switch finish the test and reboot I run the command : Show dianostic post there are 3 port failed.
Switch 1
---------
POST: MBIST Tests : Begin
POST: MBIST Tests : End, Status Passed
POST: CRYPTO Tests : Begin
POST: CRYPTO Tests : End, Status Passed
POST: PHY Loopback: loopback Test : Begin
POST: PHY Loopback: Failed For Interface : TenGigabitEthernet1/0/1
POST: PHY Loopback: Failed For Interface : TenGigabitEthernet1/0/7
POST: PHY Loopback: Failed For Interface : TenGigabitEthernet1/0/15
POST: PHY Loopback: loopback Test : End, Status Failed
There are 3 amber lights on TenG1/0/1 ,TenG1/0/7 and TenG1/0/15.
The switch image version: 16.6.4
I downgrade the switch image version to :16.6.1 but the loopback Test still failed on TenG 1/0/1
I downgrade the switch image version to : 16.3.7 but there are 2 port failed on TenG 1/0/3 and TenG 1/0/24
Is this a software issue or hardware issue ?
I have run the diagnostic test on many WS-C3850 switches and I have not encountered the problem like this WS-C3850-24XU.
Please advise.
Thanks.
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02-09-2020 08:34 PM

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02-09-2020 10:48 PM
Hi,
Check the below link, it has a good description of your issue.
https://bst.cloudapps.cisco.com/bugsearch/bug/CSCvj94357/?rfs=iqvred
Thanks,

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02-10-2020 09:27 PM
I configured port TenG1/0/1,1/0/7 and 1/0/15 to routed ports on the WS-C3850-24XU and then configured port Gig1/0/1,1/0/7 and 1/0/15 to routed port on a WS-C3850-48P-E.
The WS-C3850-24XU 3 ports LED light were amber and both switches can ping.
I also read the link B.kablawi90 has provided ( Thanks,B.kablawi90) the WS-C3850-24XU loopback test failed seem to be relate to software issue. I had used the diagnostic test for 3 different IOS Images on the same switch and the failed test port seem to be bouncing around.
If the failed test port is hardware related, no matter what IOS Image I used the failed test port should be the same port.
I could be wrong.
What is your suggestion, Leo ?
Thanks
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02-10-2020 10:03 PM
If the reboot still comes back with the same "loopback failure", then contact Cisco TAC.
Personally, I would just contact Cisco TAC and organize an RMA.
