First, check the basics—look for power issues on your optical network terminal and inspect all cables for visible damage. Many fiber internet problems come from dirty connectors or loose plugs, not major faults. This document describes how to troubleshoot fiber optic interfaces by addressing some of the fiber optic module and cabling specifications. The information in this document is based on all Catalyst 9000 Series switches. These high-speed, high-capacity communication networks are increasingly replacing copper cables, offering superior performance and. Fiber optic troubleshooting is the systematic process of identifying, diagnosing, and resolving problems within fiber optic communication networks.