I've got a pair of 3560s (one's PoE, the other's bog standard), running 12.2(25)SEE2, with the GLC-LH-SM SFPs in them. When the switches are close together (~ 2 meters or so), the link works, no problems. However, our fiber is over around 2 kilometers. We can't get the links up. Since the fiber between the sites is terminated with SC connectors, and the SFPs are (naturally) LC connectors, we've used converters as well as very short SC-LC cables with SC-SC couplers. With the converters and both switches set to nonnegotiate on gi0/1, we see a link light on one end or the other, depending on which cable we hook up.
We're currently using media converters between the two sites, which work just fine (other than the fact they're 100baseT and not ours), which indicates to me that the fiber itself is not the problem.
Do we just have bum SFP(s), or is there something I've missed in the configuration?
The config on both ends is (currently)
switchport trunk encapsulation dot1q
switchport mode trunk