Things to check if the SFP/SFP+ link is not coming up. Ensure that a compatible transceiver is used. Fiber optic networks are celebrated for their speed and reliability, but even the best systems can encounter problems. This guide will walk you through diagnosing and resolving common. We have a fibre run, SM, 650 meters, with Level1 dumb switches at each end, I get Link lights at both ends, but there's no network traffic. Switch A is on the router end, devices connected to this switch get DHCP leases and can browse the internet without issue.