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 :)