A green light usually means normal operation, while red or blinking lights signal issues. If you see a “LOS” (Loss of Signal) indicator, verify or restore power to my ONT and check all connections. Understanding fiber‑optic color codes is essential for any technician tasked with installing, maintaining, or troubleshooting modern fiber networks. Here's how it works: every. I'm trying to configure a fiber trunk between a Catalyst 3560 switch (Gi0/1) and Catalyst 3750 switch (Gi2/0/50). The SFP modules (GLC-SX-MM) are seated and the cables appear connected fine, but I get no green LED lights on either switch.
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