Which low-speed SFP matches my legacy port?
The series covers 155M, 1.25G, 2.5G, 2.67G and copper directions, with SX at roughly 550m, LX at 10km and single-mode directions reaching up to 120km. The same SFP cage carries Ethernet, Fibre Channel and SDH/SONET rates, so the host port protocol and line rate have to be confirmed, not just the connector.