Realtek r8169 always flapping

[Tim]

Allegedly, on or about 26 October 2015, Kseniya Blashchuk sent:
> I noticed in dmesg that my ethernet link is flapping all the time
> ..
> I changed the cabling, tried to plug into another switch no difference.
> Any ideas will be very appreciated as this flapping brings a lot of inconvenience. 

I would strongly suspect the network card is broken.  Flapping is a
common effect seen in busted network cards.  I've even heard it said
that it's a deliberately designed failure indicator.

They do get busted easily enough, especially if you connect equipment
between different rooms, or buildings.  There can be quite a voltage
difference between the mains wiring, many cards don't have adequate
galvanic isolation, or none at all.  And long wiring can pick up EMI
from lightning storms.

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