If the SFP link is not OK, there are five possible causes: Either a SFP has been installed but the license key does not include SFP fiber support, a fiber link could not be established even though no LOS was detected (i.e. an optical carrier was detected, which could be due to a broken TX fiber, or because the link is disabled at the fiber link partner), a fiber link could not be established and LOS is detected (i.e. no optical carrier is detected), the installed SFP is not supported or the installed SFP failed to initialize correctly. NB: a change of status may generate an SNMP trap and/or SMTP email alert