Loopback testing involves sending a signal from a source back to itself, essentially creating a closed loop. By eliminating redundant connections and interferences, with a loopback test it is possible to check and assess the functionality of the device, switch's port, or internal configuration. In. This document describes how to troubleshoot fiber optic interfaces by addressing some of the fiber optic module and cabling specifications. There are no specific requirements for this document. A SFP+ loopback module is an integrated serial data link to test the signal integrity of any given host. For more on how to complete a.