SFP vs SFP+ vs SFP28 (and SFP56/SFP112): Differences Explained

The difference between SFP vs SFP+ is speed: a standard SFP module runs at up to 1 Gbps, while SFP+ runs at 10 Gbps in the same physical size. SFP28 raises a single lane to 25 Gbps, and the newer SFP56 and SFP112 use PAM4 signalling to reach 50G and 100G, still in the same small cage.

Because all five share one footprint, they are easy to mix up on a purchase order. This guide explains what each generation carries, which modules work in which ports, the common optical and copper types at each speed, and how to pick the right part for a given link.

SFP, SFP+, SFP28, SFP56 and SFP112 at a Glance

Every module in the SFP family carries one transmit lane and one receive lane. What changes from generation to generation is the signalling rate on that lane and, from SFP56 onwards, the modulation. The cage, the latch and the overall size stay the same, which is why a 25G module looks almost identical to a 1G one.

Why the “28”, “56” and “112” names?

The numbers roughly match the electrical lane rate the cage is designed for, not the Ethernet speed. SFP28 is built for lanes around 28 Gbps, enough for 25G Ethernet plus overhead. SFP56 and SFP112 follow the same logic for 50G and 100G PAM4 lanes. The same naming appears in the QSFP world, where QSFP28 carries four 25G lanes for 100G.

NRZ vs PAM4

SFP, SFP+ and SFP28 use NRZ, which sends one bit per symbol. SFP56 and SFP112 use PAM4, which sends two bits per symbol using four signal levels. PAM4 doubles throughput without doubling the symbol rate, but it is more sensitive to noise, so 50G and 100G links depend on forward error correction (FEC) and tighter signal integrity.

Port Compatibility: Which Modules Fit Which Ports

Physically, any SFP-family module will slide into any SFP-family cage. Whether it links up, and at what speed, depends on the port’s electronics and the switch software. A link only comes up when both ends run the same speed and, at 25G and above, the same FEC mode.

• SFP module in an SFP+ port: works on most switches at 1G. Some platforms need the port speed set manually, and a few models do not support 1G on certain ports, so check the datasheet.
• SFP+ module in an SFP28 port: generally works at 10G. This is the normal way to connect 25G-capable switches to existing 10G equipment.
• SFP28 module in an SFP+ port: the port cannot run 25G. Some SFP28 optics are dual-rate and will run at 10G, but many are not, so do not plan on it.
• SFP+ module in an SFP-only port: will not run at 10G. A 1G-only port cannot be upgraded by changing the optic.
• SFP56 and SFP112 ports: usually accept lower-speed modules too, but support for 10G and 25G varies by switch or NIC. Confirm it before mixing generations.

Two more points catch people out. First, the module must be coded for the host platform, or the switch may reject it or report it as unsupported. Second, the fibre type and wavelength must match on both ends: a 10GBASE-SR at one end and a 10GBASE-LR at the other will never link, even though both are SFP+.

Common SFP Types by Speed

The suffix on a module name tells you the reach class and, by implication, the fibre type. Reaches below are IEEE figures unless marked as vendor-defined classes.

1G SFP: SX, LX and ZX

• 1000BASE-SX: 850 nm over multimode fibre, up to 550 m on OM2 (and further on OM3/OM4 per vendor datasheets). LC duplex.
• 1000BASE-LX: 1310 nm over single-mode fibre, up to 10 km. LC duplex.
• 1000BASE-ZX: 1550 nm over single-mode, typically 70 to 80 km. ZX is an industry convention, not an IEEE standard, so reach is set by each vendor.
• 1G BiDi: uses a single strand of fibre with different transmit and receive wavelengths at each end, sold in matched pairs.

Browse options in our 1G SFP transceiver range.

10G SFP+: SR, LR, ER and ZR

• 10GBASE-SR: 850 nm multimode, up to 300 m on OM3 and 400 m on OM4. The default choice inside a building.
• 10GBASE-LRM: 1310 nm, up to 220 m on older OM1/OM2 multimode. Useful when legacy fibre cannot carry SR far enough.
• 10GBASE-LR: 1310 nm single-mode, up to 10 km.
• 10GBASE-ER: 1550 nm single-mode, up to 40 km.
• 10G ZR: 1550 nm single-mode, typically 80 km. Like ZX at 1G, this is a vendor class, not IEEE.

CWDM, DWDM and BiDi versions of SFP+ also exist for fibre-constrained links. See the full 10G SFP+ range.

25G SFP28: SR and LR

• 25GBASE-SR: 850 nm multimode, up to 70 m on OM3 and 100 m on OM4 with RS-FEC enabled.
• 25GBASE-LR: 1310 nm single-mode, up to 10 km.

25G multimode reach is much shorter than 10G. If you are reusing 10G multimode cabling that runs 200 m or more, plan for single-mode 25G-LR or new fibre. Our 25G SFP28 transceivers cover SR, LR and longer-reach types.

50G SFP56 and 100G SFP112

At 50G, 50GBASE-SR reaches 100 m on OM4, while 50GBASE-FR and 50GBASE-LR cover 2 km and 10 km on single-mode. At 100G single-lane, common types include 100GBASE-SR1 for short multimode runs and 100GBASE-DR (500 m), FR1 (2 km) and LR1 (10 km) on single-mode, all with LC duplex connectors. These modules mostly appear as the far end of a 400G or 800G breakout, or on newer high-speed server NICs.

Copper RJ45 SFP Modules

Copper SFPs put an RJ45 socket in an SFP or SFP+ cage so you can run twisted-pair cable to a device with no fibre port.

• 1000BASE-T SFP: up to 100 m on Cat5e or better. Low power and widely supported. Some models also support 10/100 Mbps, but not all, so check if you need to connect older equipment.
• 10GBASE-T SFP+: runs 10G over Cat6a, but most modules are rated for around 30 m rather than the full 100 m of a native 10GBASE-T switch port. They also draw noticeably more power and run hotter than optical SFP+ modules.

Before ordering 10GBASE-T SFP+ in quantity, check that the switch supports them and whether it limits how many can sit in adjacent ports. For new 10G runs between racks, fibre or DAC is usually the better choice.

DAC and AOC Options in the SFP Family

For short links you do not need two transceivers and a patch cord. Direct attach copper (DAC) cables and active optical cables (AOC) have SFP-type ends permanently fixed to the cable.

• SFP+ passive DAC: typically sold up to 7 m. Cheapest and lowest-power option for top-of-rack to server.
• SFP28 passive DAC: up to 5 m, with RS-FEC needed on the longer lengths. Shorter cables can run with lighter FEC or none, depending on the host.
• SFP+ and SFP28 AOC: fibre-based, thinner and lighter than DAC, used for runs of tens of metres such as rack to rack.
• Breakout DAC/AOC: a QSFP+ or QSFP28 end splits into four SFP+ or SFP28 ends (4 x 10G or 4 x 25G).

We compare these options in detail in our guide to DAC vs AOC vs optical transceivers, and you can browse ready-made DAC and AOC cables.

How to Choose Between SFP, SFP+ and SFP28

Start from the port, not the module. The highest speed your switch or NIC port supports, and the speed of the device at the other end, decide the generation. Distance and existing fibre then decide the type.

Typical choices

• Campus access and small offices: 1G SFP (SX or LX) for uplinks, 10G SFP+ where the access switch has 10G uplink ports.
• Enterprise server rooms: 10G SFP+ DAC inside the rack, 10GBASE-SR between racks, 10GBASE-LR between buildings.
• Data centre server access: 25G SFP28 is now the standard server speed in many leaf-spine designs, with 100G or 400G uplinks.
• New high-density builds: 50G SFP56 or 100G SFP112 on servers that connect to 400G or 800G switches through breakout.

Buyer’s checklist

1. Note the exact switch or NIC model and port type at both ends of the link.
2. Confirm the speed both ends will run, including any 1G or 10G fallback you need.
3. Measure or estimate the link length, including patch panels.
4. Identify the fibre: OM3, OM4 or single-mode, and LC or another connector.
5. Pick the type (SR, LR, ER and so on) that covers the distance with some margin.
6. Choose DAC or AOC instead of optics for in-rack and adjacent-rack runs.
7. Ask for the module to be coded for your platform and tested before delivery.

If you are planning wider changes, our enterprise networks team can help size uplinks, and the QSFP transceivers guide covers the four-lane modules your uplinks will use.

Frequently Asked Questions

Can I use an SFP module in an SFP+ port?

On most switches, yes: an SFP+ port will run a 1G SFP module at 1G. Some platforms need the port speed set manually and a few ports do not support 1G at all, so check the switch datasheet first.

Can I put an SFP+ module in an SFP28 port?

Yes, SFP28 ports generally accept SFP+ modules and run them at 10G. The device at the other end must also run at 10G, as the link will not come up at mismatched speeds.

Is SFP28 backward compatible with SFP+?

An SFP28 port is usually backward compatible with SFP+ modules at 10G. The reverse is not reliable: an SFP28 module in an SFP+ port can only work at 10G and only if the module itself is dual-rate.

What is the maximum distance of a 25G SFP28 SR module?

25GBASE-SR reaches 70 m on OM3 and 100 m on OM4 multimode fibre with RS-FEC enabled. For longer links, use 25GBASE-LR on single-mode fibre, which reaches 10 km.

How far can a 10GBASE-T copper SFP+ module run?

Most 10GBASE-T SFP+ modules are rated for about 30 m on Cat6a cable. They also draw more power than optical SFP+ modules, so check switch support before deploying many of them.

Talk to TIFNEX

Send us your switch or NIC models, link distances and quantities, and our engineers will match the right SFP, SFP+, SFP28 or DAC for each port, coded for your platform and tested before it ships. We quote within 24 hours and deliver across the UAE, Egypt and the wider GCC. Contact our team or message us on WhatsApp at +971 54 300 8970.