SFP
Small Form-factor Pluggable
A compact, hot-swappable transceiver module that plugs into a switch or router cage to provide fibre optic or copper connectivity — making the physical link type field-replaceable without changing hardware.
SFP modules separate the transceiver from the switch hardware. Instead of a fixed RJ45 copper port, an SFP cage accepts whichever transceiver you insert — multimode fibre for a 300m run to a building, single-mode fibre for a 10 km campus link, or a copper SFP for a short patch. The same switch port serves all use cases. SFP is hot-swappable: you can replace a module while the switch is running. This flexibility made SFP the standard for switch uplinks, NAS connections, and inter-rack cabling in data centres.
SFP form factor comparison
| Form factor | Max speed | Common use |
|---|---|---|
| SFP (1G) | 1 Gbps | Gigabit uplinks, older infrastructure |
| SFP+ (10G) | 10 Gbps | Server/NAS to switch, enterprise uplinks |
| SFP28 (25G) | 25 Gbps | Server uplinks, spine-leaf data centres |
| QSFP+ (40G) | 40 Gbps | Switch-to-switch, aggregation layer |
| QSFP28 (100G) | 100 Gbps | Core switches, data centre spine |
| QSFP-DD (400G) | 400 Gbps | Hyperscale data centres |
Optical SFP types by distance
SFP optical modules are differentiated by wavelength and fibre type. SR (Short Range) uses 850 nm multimode fibre — up to ~300 m, cheaper transceivers and cable. LR (Long Range) uses 1310 nm single-mode fibre — up to 10 km. ER (Extended Range) reaches 40 km. ZR/ZX reaches 80 km+. BiDi (Bidirectional) SFPs use a single fibre strand with different wavelengths for TX and RX — halving fibre cabling costs. For home and small office use, SFP+ with DAC cables is the most cost-effective way to achieve 10 GbE between a NAS and a switch within a rack.
Frequently Asked Questions
What is the difference between SFP, SFP+, SFP28, and QSFP?
Primarily speed. SFP = 1 Gbps, SFP+ = 10 Gbps (most common in enterprise/prosumer), SFP28 = 25 Gbps, QSFP+ = 40 Gbps, QSFP28 = 100 Gbps. All are hot-swappable but not interchangeable — each form factor has its own cage size.
What is a DAC cable and when should I use it instead of SFP?
A DAC (Direct Attach Copper) cable has SFP+ connectors permanently attached to a twinax copper cable. Cheaper and lower power than optical for runs up to ~7 m — ideal for server-to-switch within a rack. Use optical SFPs for longer runs or between buildings.
Do I need to buy the same brand SFP as my switch?
Cisco and Juniper may lock out non-branded modules via EEPROM vendor checks. Prosumer switches (Ubiquiti, MikroTik, Netgear) almost always accept third-party SFPs without issue. Reputable third-party vendors program compatible vendor IDs and are widely used in enterprise environments.