As soon as a network extends beyond a few meters or increases in speed, fiber optics become essential — along with the well-known SFP modules. SFP, SFP+, SFP28, QSFP… these small transceivers that plug into your switches’ ports often confuse users due to their many variants. This guide clarifies the differences in speed, the choice between fiber and copper, compatibility between brands, and how to select the right module — new or tested used.
What is an SFP module (transceiver)?
An SFP module (Small Form-factor Pluggable) is a removable transceiver that plugs into the SFP port of a network switch, router, or server. It converts the internal electrical signal into an optical (fiber) or electrical (copper) signal for transmission over the cable. Its major advantage: it is hot-swappable and modular — you can choose the type of connection (distance, speed, medium) without changing the equipment.
SFP, SFP+, SFP28, QSFP, QSFP28: what are the speed differences?
The main difference between these formats is the speed they support:
- SFP: up to 1 Gbit/s (Gigabit Ethernet). The historical standard for 1G fiber links.
- SFP+: 10 Gbit/s. The most common today for uplinks and 10G fiber.
- SFP28: 25 Gbit/s. For recent high-speed infrastructures.
- QSFP+: 40 Gbit/s (4 channels of 10G).
- QSFP28: 100 Gbit/s (4 channels of 25G). Reserved for core networks and data centers.
SFP and SFP+ share the same physical size: an SFP+ port generally accepts a 1G SFP module, but not vice versa. QSFP modules are wider and designed for very high speeds.
Fiber or copper? Optical, DAC, and RJ45
Single-mode or multimode fiber
Multimode fiber (OM3/OM4, transceivers at 850 nm) covers short distances — typically up to 300-400 m — at a lower cost, ideal for within-building use. Single-mode fiber (OS2, 1310/1550 nm) covers several kilometers, used to connect buildings or sites. The module must match the type of fiber installed.
The DAC cable (Direct Attach Copper)
To connect two nearby devices (a few meters, in a rack), the DAC cable integrates SFP+ connectors directly at both ends: cheaper and less power-consuming than a pair of optical modules plus fiber.
The copper SFP (RJ45)
An RJ45 SFP module allows connecting a standard copper Ethernet link to an SFP port — useful for mixing fiber and copper on the same switch.
How to read an SFP module’s specifications
Before buying, check these points on the datasheet:
- Speed: 1G, 10G, 25G, 40G, 100G — it must be supported by the switch port.
- Medium type: single-mode, multimode, DAC, or copper.
- Wavelength: 850 nm (multimode), 1310/1550 nm (single-mode).
- Maximum distance: from 100 m to several tens of km depending on the module.
- Connector: usually LC duplex (or sometimes BiDi on a single fiber).
- DOM/DDM: digital monitoring (optical power, temperature) facilitates diagnostics.
Compatibility and manufacturer coding: the tricky point
This is the most common mistake. Many manufacturers (Cisco, HPE/Aruba…) “code” their modules: a switch may reject an unrecognized transceiver. Practically, a module must be coded for the brand and often the model of the switch it is used with. Before buying, identify your equipment’s exact reference and check the module’s announced compatibility. If in doubt, ask us: we verify compatibility before shipping.
How to choose your SFP module: the checklist
- What speed? (matched to the switch port: SFP+ for 10G, etc.)
- What distance to cover? (short-distance multimode vs. long-distance single-mode)
- Is fiber already installed or to be installed? (the module follows the fiber type)
- What brand/model of switch? (manufacturer coding)
- Short connection in a rack? → consider DAC instead of two optical modules.
For compatible active equipment, see our Cisco switches and HP/HPE/Aruba switches, and if you’re still unsure about the switch itself, read our guide managed or unmanaged switch: how to choose.
Used SFP modules: save without risk
New professional transceivers are expensive, especially manufacturer-coded ones. Tested used modules offer significant savings for a component that hardly wears out. Every module we offer is checked and guaranteed. Discover our selection of used SFP, SFP+, and transceiver modules, and for general context on buying used equipment, see our guide to used IT equipment.
FAQ: SFP modules
What is the difference between SFP and SFP+?
SFP supports up to 1 Gbit/s, SFP+ up to 10 Gbit/s. They have the same size: an SFP+ port often accepts a 1G SFP module, but a 1G SFP port does not accept a 10G module.
Does a Cisco SFP module work on an HPE switch?
Not always: many switches only accept modules coded for their brand. You need a transceiver coded for the switch’s manufacturer (and often model). Check compatibility before purchase.
Single-mode or multimode fiber: which to choose?
Multimode (850 nm) for economical short distances within buildings; single-mode (1310/1550 nm) to connect sites over several kilometers. The module must match the installed fiber.
What is a QSFP module for?
QSFP+ (40G) and QSFP28 (100G) are used for very high-speed links, typically between core network switches or in data centers.
In summary
Choosing an SFP module means aligning four parameters: speed (SFP/SFP+/SFP28/QSFP), medium (multimode, single-mode, DAC, or copper), distance, and compatibility with the switch brand. Once these points are verified, installation is immediate thanks to hot-swap. And for budget, tested used modules offer the best value for money.