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Dip switch 1 is auto-negotiation of speed and duplex and that was left enabled=UP. Set switches 2, 3 and 4 DOWN on both converters,
to disable pause control, link pass-through and far-end fault.
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With 1=UP, and 2,3,4=DOWN and power cycling both units, the link came back and we could ping the seatainer. Swapped data boxes and then couldn't ping. Eventually power cycled the 5 port switch at the tower and things worked again.
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