What is a combo SFP port?

A Combo port is a single interface with a dual front - RJ45 port or SFP port, so it supports both copper and fiber SFP connections. In other words, it is a composite port that can support two different physicals, sharing the same switch fabric and port number. But these two different physical ports cannot be used at the same time. Each dual combo port is an interface that provides two connection options: RJ-45 connection for copper Ethernet cable and SFP connection for fiber optic cable. For example, if a combo SFP port is being used, the corresponding copper port is automatically disabled and vice versa. The figure below shows the 4*1GE Combo port of the FS S3800-24F4S SFP stacking switch.