In short: 25G Ethernet (25GbE) runs at 25 Gbit/s over a single lane, using SFP28 modules that are the same size as 10G SFP+. It gives servers two and a half times the bandwidth of 10G over the same kind of cabling, which is why it replaced 10G as the standard server connection in modern data centers.
Here is where 25G fits between 10G and 100G, and what you need to use it.
Why 25G exists
For years the path was 1G, then 10G, then 40G. But 40G bundles four 10G lanes, which makes the optics wider and more expensive per port. 25G took a different route: one faster lane in the small SFP28 module. The result is more bandwidth per port, lower cost per bit and the same port density as 10G.
25G also fits neatly into 100G: a 100G QSFP28 module is built from four 25G lanes. That makes it easy to connect servers at 25G to switches with 100G uplinks.
25G compared with 10G, 40G and 100G
| Speed | Module | Lanes | Typical use |
|---|---|---|---|
| 10G | SFP+ | 1 × 10G | uplinks, older servers |
| 25G | SFP28 | 1 × 25G | server connections |
| 40G | QSFP+ | 4 × 10G | aggregation, older spine links |
| 100G | QSFP28 | 4 × 25G | spine and core links |
25G SFP28 module types
- SR – multimode fiber, 850 nm, about 100 m: the standard choice inside a data center.
- eSR – multimode, up to 300 m for longer runs.
- LR – single-mode fiber, 1310 nm, 10 km.
- ER – single-mode, 40 km.
- BiDi versions that use a single fiber – see BiDi transceivers explained.
Moving from 10G to 25G
- Check the ports: 25G needs SFP28 ports on both the switch and the server network card. Many SFP28 ports also run 10G SFP+ modules, so you can migrate step by step.
- Check the fiber: 25G SR runs about 100 m over OM4 multimode fiber – shorter than 10G SR – so measure long multimode runs. Single-mode links with LR reach 10 km as before. More in single-mode vs multimode.
- Both ends at 25G: a link only comes up at 25G when both modules are 25G.
- Coded for your equipment – see our SFP compatibility guide.
Frequently asked questions
Is 25G Ethernet backward compatible with 10G?
The ports often are: many SFP28 ports accept 10G SFP+ modules. The modules themselves are usually made for one speed, so both ends of a link should use the same type.
What is the difference between SFP+ and SFP28?
Same size, different speed: SFP+ runs at 10 Gbit/s, SFP28 at 25 Gbit/s. See SFP vs SFP+ vs SFP28 vs QSFP28.
Is 25G better than 40G?
For server connections, usually yes: it uses one lane in a smaller module, costs less per port and fits into 100G networks. 40G is still common between older switches.
