SFP28

SFP28 is a hot-pluggable transceiver that provides a single 25 Gbit/s serial link in the familiar small form-factor pluggable (SFP) package. It was introduced to support 25G Ethernet and related high-speed interconnects while allowing reuse of existing SFP/SFP+ cages and host circuitry.

Technical characteristics: The module uses the same 20-pin electrical interface and mechanical footprint as SFP and SFP+ modules, enabling insertion into SFP-compatible slots. The designation “28” reflects the family name, while the practical data rate is 25 Gbit/s per lane. SFP28 devices come in optical versions for fiber and in direct-attach copper (DAC) forms. Optical variants support multimode fiber (SR, typically 850 nm) and single-mode fiber (LR and ER, typically 1310 or 1550 nm, depending on the model) to cover short to long reach.

Applications: SFP28 is primarily employed for 25G Ethernet connections, including server NIC to switch links and switch-to-switch uplinks. It is compatible with breakout configurations that enable a single 100G port to connect to four 25G SFP28 ports, or conversely to aggregate four 25G links into a 100G connection. Some storage and interconnect applications also utilize 25G rates where applicable.

Compatibility and standards: SFP28 is designed to be compatible with the SFP/SFP+ ecosystem, but operation at 25G requires host controller and NIC support as well as matching optics. While mechanically compatible, not all SFP+ ports guarantee 25G negotiation; firmware, silicon, and optics must align to enable 25G functionality.

See also: SFP+, QSFP28, DAC cables, 25G Ethernet.