I have a really weird problem with a fiber connection.
I have 2x2 fibers OM4 G50/125 between two rooms, room A & B (fiber length approximately 20m).
I have two switches, a Huawei CE6810 and a HP 2530-48G-2sfp+ (each has a sfp+ module).
1) When I have the switches side by side, connected via fiber it works.
2) When I have one switch in room A, and the other in room B connected via fiber it does not work
HUAWEI -- A ---------- B -- HP
A = room A, B = Room B, - = fiber connection
3) When I connect one of the fiber pairs between the rooms to the other one (so both ends in Room A) and connect both switches it works.
HUAWEI -- A ---------- B | HP-- A ---------- B
This utilizes the same fiber connection, the total length is just double. I have no idea how to even start looking for the problem.