SFP, SFP+ and SFP28 modules look almost identical and fit the same size of cage. The difference is the data rate they carry, and whether a given port will accept them. This guide sets out what fits where.
The short answer
- SFP: 1 Gb/s (Gigabit Ethernet)
- SFP+: 10 Gb/s
- SFP28: 25 Gb/s
- All three share the same physical size, so the module fits mechanically in any of the three port types.
- Whether a module works depends on the speeds the port supports, not on whether it fits.
Side by side
| SFP | SFP+ | SFP28 | |
|---|---|---|---|
| Data rate | 1 Gb/s | 10 Gb/s | 25 Gb/s |
| Typical use | access ports, uplinks on older switches | server and uplink ports | server ports in newer data centres |
| Common optics | 1000BASE-SX, LX, EX, ZX, T, BX | 10GBASE-SR, LR, ER, ZR, LRM, BX | 25GBASE-SR, LR, CSR |
| Copper option | 1000BASE-T (RJ-45, 100 m) | 10G DAC; 10GBASE-T (30 m, high power) | 25G DAC |
| Forward error correction | not used | not used | often required (RS-FEC or FC-FEC) |
What fits where
- SFP module in an SFP port: works at 1G.
- SFP+ module in an SFP+ port: works at 10G.
- SFP module in an SFP+ port: usually works at 1G, if the switch supports 1G on that port. Many do, but some 10G-only ports do not.
- SFP+ module in an SFP28 port: usually works at 10G, if the port supports 10G. Most SFP28 ports do.
- SFP28 module in an SFP+ port: does not run at 25G. Some SFP28 optics are dual-rate and run at 10G, but many are 25G only.
- SFP+ module in an SFP port: does not work. A 1G-only port cannot run 10G.
The rule of thumb: a faster port can usually run a slower module; a slower port cannot run a faster one. Always check the platform's optics compatibility guide for your exact hardware and software release.
Matching the two ends of a link
- Both ends must use the same standard, for example SR to SR or LR to LR. You cannot mix an SR optic at one end with an LR optic at the other.
- Both ends must run at the same speed. A 25G port connected to a 10G port needs the 25G port set to 10G, and a dual-rate optic or a 10G optic in it.
- BiDi optics are the exception: they come in pairs with different transmit wavelengths, one upstream (U) and one downstream (D).
Choosing between them
- Building a new server or leaf layer? SFP28 at 25G costs little more than 10G and gives two and a half times the bandwidth.
- Adding to an existing 10G network? SFP+ keeps everything consistent.
- Connecting cameras, access points or legacy kit? SFP at 1G, or 1000BASE-T for copper.
- Links inside the same rack? Consider a DAC cable instead of two optics plus a patch cord.
Fibre types in brief
- SR optics use multimode fibre (OM3/OM4): reach is hundreds of metres, and the optics cost less.
- LR, ER and ZR optics use single-mode fibre (OS2): reach is from 10 km up to about 80 km.
- Check the fibre already installed before choosing: an SR optic on single-mode fibre, or an LR optic on multimode fibre, will not give you a reliable link.