linkFlapErrDisabled on Cisco Nexus

I once noticed that the port is periodically disconnected on the Cisco Nexus N3K-C3064PQ-10GX switch, there are a lot of records in the logs that the link was falling and rising, I looked at the status of the port:

show interface ethernet 1/18

And I saw that the switch turned it off due to frequent down/up:

Ethernet1/18 is down (linkFlapErrDisabled)

Last link flapped 18:41:00

To enable the port, I ran the commands:

interface ethernet 1/18
no shutdown

The link on the port appeared and the port worked for half a day and then the error repeated itself.
Then I looked at the SFP module information:

show interface ethernet 1/18 transceiver details
          SFP Detail Diagnostics Information (internal calibration)
                Current              Alarms                  Warnings
                Measurement     High        Low         High          Low
  Temperature   39.42 C        80.00 C    -10.00 C     75.00 C       -5.00 C
  Voltage        3.26 V         3.57 V      2.98 V      3.48 V        3.07 V
  Current       43.91 mA       90.00 mA     5.00 mA    80.00 mA      10.00 mA
  Tx Power       1.48 dBm       4.98 dBm   -4.00 dBm    3.98 dBm     -3.00 dBm
  Rx Power     -17.69 dBm --    0.00 dBm  -16.02 dBm   -1.00 dBm    -14.08 dBm
  Transmit Fault Count = 0

In my case, the problem turned out to be a bad optical signal, which caused the link flapped.
The engineer cleaned the optical connector in the SFP module and the signal returned to normal, became -9.

I also had a similar problem when I needed more than 40G ports and I tried to connect the Breakout cable 4x10g-1x40g to 10G ports, but as it turned out, the ports of this switch did not support Breakout, only the last 4, but they were used under 40G:

hardware profile portmode ?
  48x10g+4x40g  48x10G+4x40G port mode
  52x10g+3x40g  52x10G+3x40G port mode
  56x10g+2x40g  56x10G+2x40G port mode
  60x10g+1x40g  60x10G+1x40G port mode
  64x10g        64x10G port mode

show interface ethernet 1/1 capabilities | i Breakout
  Breakout capable:      no

And accordingly, where the Breakout cable was connected – the links on the ports were constantly flapping. As a way out of the situation, it was possible to connect 4×10 to any ports of the Cisco switch, and disassemble the 40g link on another device into 4x10g into aggregation (for example, if it is an Intel network adapter), but I didn’t do such nonsense and just installed another Juniper QFX5100 switch to increase the number of 40G ports.

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