I have a system which looks like that:

CPU(macbook)<-->thunderbolt<-eth->ethernet media converter<-fiber->ethernet media converter<-eth->raspberry pi 2.

Both CPU and RP2 have static IPs.

If I connect an ethernet cable from my computer to the RP2 directly there is no problem, I can ping it and ssh it.

The fiber is duplex and I tried with different length (0.5, 50 and 100m) and for the 50 and 100m there is an adaptor from LC/ST because I don't have LC/LC long duplex fibers.

I tested the fibers and they are not broken since I can see light coming out. The media converters seem to communicate since the FXLINK led is blinking in both of them when I try to ping the system. I have tried disabling both firewalls from the CPU and RP2 but still the same issue. When I try to ping them I get timeout messages or similar to "No route to host" and "Host unreachable".

These are the media converters and SFP modules I am using: https://www.versatek.com/hardened-micro-1000base-t-to-1000base-sfp-ethernet-media-converter.html https://www.versatek.com/sfp-port-1000base-lx-mini-gbic-module-10km-40-75.html

The fiber is a simple patch cable and a more professional cable from the company FOSS but the 0.5m patch cable is always connected with the adaptor:

example: fiber media<-(LC-fiber(0,5)-LC)-(LC/ST adaptor)-(ST-fiber(50 or 100)-LC)-fiber media.

I hope the information I gave you is enough

Thank you for your help :)

  • \$\begingroup\$ Remove as many variables as you can. Drop the eth-fiber adapters and just use an ethernet cable. If it works, and you know your fiber cable is fine, then its the adapters. \$\endgroup\$
    – Funkyguy
    Jan 20, 2016 at 15:00

1 Answer 1


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.
  • \$\begingroup\$ True! That makes sense since I just connected the system to another computer which I guess can handle 1000M. That also explains why when I connect a 100M eth switch it does not work anymore. I'll follow your advice. I thought these devices could adapt their speed. Good learning. Thanks a lot! \$\endgroup\$
    – borias23
    Jan 20, 2016 at 14:34
  • \$\begingroup\$ you're missing the obvious, and probably even price effective choice: 4. replace the Pi with something that has Gigabit ethernet and more CPU power (what would you do with Gigabit on your Pi, anyway?), for example an Odroid XU4. \$\endgroup\$ Jan 20, 2016 at 14:34
  • \$\begingroup\$ That is also a good solution which I had in mind some time ago. Thank you Marcus \$\endgroup\$
    – borias23
    Jan 20, 2016 at 14:42

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