What Is SFP?

SFP, short for small form-factor pluggable, is a standard slot and the matching plug-in transceiver used to connect network equipment over fibre or copper. An SFP port on a switch, router or network card is an empty cage until a module goes in, and the module decides what kind of link the port makes. SFP modules are hot-swappable, so they can be fitted or changed with the equipment running.

SFP is not an IEEE standard. It is defined by a multi-source agreement (MSA), a specification written jointly by component makers so modules from different vendors fit the same cage. The original SFP carries up to 1 Gbit/s. SFP+, the same size, carries 10 Gbit/s, and SFP28 carries 25 Gbit/s.

Choosing the module chooses the link: a multimode fibre module for runs within a building, a single-mode module for links of many kilometres between sites, or a copper module for a standard Ethernet cable. Because modules can be changed without replacing the switch, one switch can suit many installations.

An SFP port is a metal cage on the front of a switch or card with an edge connector at the back. The module slides in, latches, and presents its own connector to the outside: usually a duplex LC socket for fibre, or an RJ45 socket for copper. Many switches have combo ports, where an RJ45 port and an SFP cage share one switch port and whichever is connected is used. On industrial switches, SFP ports are most often the uplinks that link one cabinet back to another or to the control room, often arranged as a fibre ring so the network survives a single cut.

Modules are named by speed, media and reach. The common 1 Gbit/s types are below; SFP+ versions follow the same pattern at 10 Gbit/s.

A copper SFP, also called an SFP to RJ45 module or a 1000BASE-T SFP, puts an Ethernet PHY and an RJ45 socket inside the module, so an SFP cage can take an ordinary twisted-pair cable of up to 100 m. It is the usual answer when a switch has spare SFP cages but no free RJ45 ports, or when one end of a link has to land on copper equipment. Our Ethernet switch boards with SFP sockets, for example, take either fibre modules or copper SFPs.

Three details catch people out:

The SFP shape has been reused for faster links, and larger QSFP modules bundle four lanes for higher speeds. The port and module speeds must match, although many SFP+ ports also accept 1 Gbit/s SFP modules.

For a 10GbE link, our SFP+ vs RJ45 FAQ compares fibre and copper on power, latency and reach.

SFP ports let an industrial network run fibre between cabinets and buildings where copper would be too short or too noisy.

Many of our managed industrial switches include SFP or SFP+ ports for fibre uplinks, and our rack-mount industrial switches add 10G SFP+ ports for the core of a site network. SFP+ is not only for switches: several of our edge AI computers have dual 10GbE SFP+ ports, so a vision or analytics system can take a fibre link straight into the computer, and our 10GbE networking FAQ explains when that bandwidth is worth having. Check whether a switch accepts any MSA-compliant module or expects its own coded optics before ordering spares.

We supply industrial switches and edge computers with the SFP modules, fibre type and reach matched to the site as standard. Send us your distances and cabinet conditions, and we will specify the ports and optics to match.