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:
configure
interface ethernet 1/18
shutdown
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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