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I have a network connection extended via Fibre Optic (LC, singlemode) cables using two Standalone Media Converters like the MC210CS from TP-Link to bridge the Ethernet to Fibre and again back from Fibre to Ethernet. When I connect my MacBook Pro to the extended Ethernet, the connection gets established immediately and a IP gets assigned via DHCP, however any RPi 2 or 3 doesn't even detect the network connection at all? I suspect it's some kind of issue regarding to the negotiating protocols supported, however it does not make sense to me in terms of the NIC not even detecting the link status as being up.

Any ideas?

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    That media converter will do 10/100/1000 Mbps. The RPi is limited to 100 Mbps. Could it be that the media converter and/or ports at the other end are configured for 1 Gbps only? That would explain the MacBook Pro working and not the RPi. Do you get link lights?
    – bobstro
    Mar 16 '17 at 19:06
  • Thanks, that sounds really reasonable! The other side is not configured for 1000 particularly, but I guess the remote media converter and the connected Ethernet-Switch established the initial connection in 1000Mbps.
    – t0bias
    Mar 17 '17 at 21:43
  • I am pretty sure bobstro is wrong, there is no mention of speeds other than 1000 in the specifications for the media converter. Mar 20 '18 at 19:15
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Copied from my answer at https://electronics.stackexchange.com/questions/212437/media-converter-eth-fiber-problem-in-communication

I think you have a speed mismatch issue.

Unlike most twisted pair ethernet equipment gigabit media converters are usually single speed devices. I'm not positive as to the reasoning but I think there were substantial changes on the fiber side that made supporting both systems in the same media converter difficult. This is a problem as the ethernet controller on Pi models up to and including the 3B is a 10/100 device while your media converters are gigabit devices.

I see four possible soloutions.

  1. Use a USB gigabit ethernet adaptor on the Pi.
  2. Use a gigabit switch between the Pi and media converter.
  3. Replace the media converters with 100 Mbps models.
  4. Replace the Pi with a "raspberry pi 3 model B+" which has a gigabit Ethernet controller.

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