Typically, single mode SFP modules are labeled as "SM" or "single mode," while multimode modules may be labeled as "MM" or "multimode. To determine if your SFP (Small Form-factor Pluggable) module is single mode or multimode, you can look for specific markings or labels on the module itself. The distinction is important as it affects network performance, distance, and overall cost. This guide explains how to identify them by appearance, labeling, and technical specifications, helping you make the right choice for your installation. Identifying Single-Mode (SMF) vs. Multimode (MMF) SFP modules involves a cross-referencing protocol of physical bail colors, EEPROM telemetry, and wavelength specifications. Precise verification prevents "Ghost Links" and Mode Field Diameter (MFD) mismatches that degrade 800G AI fabric performance.