What is SFP28? The Complete 25GbE Transceiver Guide for Enterprise Networks
SFP28 is the 25 Gigabit per second successor to SFP+ (10G). It uses the same physical footprint as SFP+ but runs at 25Gbps per lane — the bandwidth-per-port sweet spot for modern server access networking. This guide covers SFP28 module types, cable choices, compatible switches, and when to move from 10G to 25G.
What is SFP28?
SFP28 (Small Form-factor Pluggable 28) is a fiber optic and copper transceiver form factor standardized for 25 Gigabit Ethernet (25GbE) and 25G Fibre Channel (32GFC). It uses the same physical cage and connector dimensions as SFP+ (10G), but the electrical interface runs at 25 Gbps per lane instead of 10 Gbps.
The "28" refers to the 25.78125 Gbps line rate used in 25GbE (25G data + 8b/10b or 64b/66b encoding overhead), not to a generation number.
Key specifications:
- Data rate: 25 Gbps
- Physical footprint: identical to SFP+
- Connector: LC duplex (fiber) or direct-attach copper
- Standard: IEEE 802.3by (25GbE), SFF-8402 (electrical)
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SFP28 vs SFP+ vs QSFP28: Form Factor Hierarchy
| Form Factor | Speed | Lanes | Use Case |
|---|---|---|---|
| SFP+ | 10 Gbps | 1 | Server access 10G, storage 10G |
| SFP28 | 25 Gbps | 1 | Server access 25G, modern NIC ports |
| QSFP+ | 40 Gbps | 4× 10G | Aggregation, inter-switch 40G |
| QSFP28 | 100 Gbps | 4× 25G | Spine/leaf 100G, storage backend |
| QSFP-DD | 400 Gbps | 8× 50G | Hyperscale spine, 400G campus core |
The 25G/100G tier (SFP28 for servers, QSFP28 for uplinks) has become the dominant tier in modern enterprise data centers — replacing the earlier 10G/40G tier for new builds in 2026.
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SFP28 Module Types
SR (Short Range) — Multimode Fiber
- Standard: 25GBASE-SR (IEEE 802.3by)
- Fiber type: OM3 or OM4 multimode (850nm VCSEL)
- Max distance: 70m on OM3, 100m on OM4
- Connector: LC duplex
- Common model: Cisco SFP-25G-SR-S, Mellanox MMA2P00-AS
Use for: server-to-ToR (top-of-rack) switch connections within a data center row or between adjacent rows. The 70–100m reach covers virtually all intra-data-center distances.
LR (Long Range) — Single-mode Fiber
- Standard: 25GBASE-LR (IEEE 802.3by)
- Fiber type: OS2 single-mode (1310nm)
- Max distance: 10km
- Connector: LC duplex
- Common model: Cisco SFP-25G-LR-S, Finisar FTLF8536P4BCV
Use for: campus inter-building links, data center interconnect within a campus where multimode fiber was not run, or where distances exceed 100m.
ER (Extended Range) — Single-mode Fiber
- Standard: 25GBASE-ER
- Fiber type: OS2 single-mode
- Max distance: 40km
- Connector: LC duplex
Use for: metro-distance data center interconnect or campus-to-campus links up to 40km.
DAC (Direct Attach Copper) — Passive and Active
- Standard: SFF-8402
- Media: twinaxial copper cable with integrated SFP28 connectors
- Max distance: 3m passive, 5m active
- No optics required — lowest cost and latency option
Passive DAC (most common):
- Lengths: 0.5m, 1m, 2m, 3m
- Cost: $15–$40 depending on length and brand
- Use for: server-to-ToR switch in same rack or adjacent rack
Active DAC:
- Lengths: 5m
- Has active signal conditioning circuitry
- Use for: cross-aisle connections where passive DAC is too short
DAC is the default choice for server-to-ToR connections in the same or adjacent rack. It is lower latency than optical (no serialization overhead) and significantly cheaper.
AOC (Active Optical Cable)
- Integrated fiber cable with SFP28 transceivers at each end
- Max distance: 30m or 100m depending on model
- Lighter and more flexible than DAC at longer distances
- Use for: distances 5–30m where DAC is too short but SR optical modules are overkill
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SFP28 Compatible Switches
| Switch | SFP28 Port Count | Max Speed | Notes |
|---|---|---|---|
| Cisco Catalyst 9300X | 2–4 (via NIM) | 25G | NIM-4S-XL module required |
| Cisco Nexus 93180YC-FX | 48 | 25G | Standard 25G ToR switch |
| Cisco Nexus 9336C-FX2 | 36× 100G QSFP28 (breakout to 25G) | 100G/25G | Spine with 25G breakout |
| Arista 7050CX3-32S | 32× 100G + 2× 10G | 25G via QSFP28 breakout | |
| Mellanox SN2700 | 32× 100G QSFP28 | 25G via breakout | |
| HPE FlexFabric 5940 | 48× 25G SFP28 | 25G | Native 25G ToR |
| Juniper QFX5120-48Y | 48× 25G SFP28 | 25G | Native 25G ToR |
Important: many 100G QSFP28 ports can be broken out into 4× 25G SFP28 ports using a QSFP28-to-4×SFP28 breakout cable. This effectively gives you 25G server connections from a 100G spine switch — a common cost-optimization for leaf/spine deployments.
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Server NIC Compatibility
SFP28 is the standard interface for 25GbE server NICs:
| NIC | Chipset | Ports | Notes |
|---|---|---|---|
| Mellanox ConnectX-4 Lx | Mellanox | 1/2× 25G | Common server NIC, also supports 10G SFP28 |
| Mellanox ConnectX-5 | Mellanox | 1/2× 25G | RoCEv2 support for RDMA |
| Intel X722 | Intel | 2/4× 25G | |
| Broadcom 57414 | Broadcom | 2× 25G | OCP 3.0 mezzanine variant common |
| HPE 631FLR-SFP28 | Mellanox | 2× 25G | OCP 2.0, common in DL380/DL360 Gen10 |
Most modern server NICs ship with SFP28 cages. They are backward compatible with SFP+ (10G) modules — a Mellanox ConnectX-4 Lx will auto-negotiate to 10G with an SFP+ module inserted. This simplifies migration: you can run 10G today and upgrade the switch-side transceiver when ready.
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When to Upgrade from 10G to 25G
Move to 25G when:
- Server-to-switch bandwidth is a measured bottleneck (sustained NICs at 9+ Gbps)
- Deploying NVMe-oF (NVMe over Fabrics) storage — requires RDMA NICs, typically 25G+
- Running VMware vSAN or Ceph with multiple 25G/50G+ storage IO streams
- New server deployment where 25G NICs cost only marginally more than 10G
- Building a leaf/spine fabric where 25G server access and 100G uplinks make the math clean
Stay on 10G when:
- Existing infrastructure is 10G and utilization is under 60%
- Budget is constrained — 10G switches and transceivers are significantly cheaper refurbished
- Workloads are latency-sensitive but not bandwidth-hungry (10G is fine for most web/app tiers)
The economics in 2026: a 25G server NIC (ConnectX-4 Lx, refurbished) costs $80–$150 — comparable to a quality 10G NIC. The switch cost difference between a 48-port 10G switch (Cisco 9300) and a 48-port 25G switch (Nexus 93180YC-FX) is larger — plan $3,000–$8,000 more for a 25G ToR — but for new builds it is usually the right long-term investment.
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Third-Party vs OEM Transceivers
OEM-branded transceivers (Cisco-branded, HPE-branded) carry a list-price premium of 200–400% over compatible third-party transceivers. They are electrically identical — the only difference is the EEPROM encoding that identifies the manufacturer.
Cisco switches will show a warning message when a non-Cisco transceiver is inserted but will operate normally unless you have enabled service unsupported-transceiver with the error-disable action. Third-party 25G SFP28 SR modules from companies like FS.com, 10Gtek, and Finisar (now II-VI) perform identically to Cisco-branded equivalents.
Pro Disk Network stocks both OEM and compatible 25G SFP28 SR/LR transceivers and DAC cables for Cisco, HPE, Mellanox, and Arista platforms.
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Frequently Asked Questions
Is SFP28 backward compatible with SFP+ ports? Physically yes — an SFP28 module fits in an SFP+ cage. However, the port will link at the lower speed (10G, not 25G) unless both the port and module support 25G. Check your switch/NIC specifications.
Can I use a 10G SFP+ module in an SFP28 port? Yes — most SFP28 ports auto-negotiate to 10G when an SFP+ module is inserted.
What fiber do I need for SFP28 SR? OM3 or OM4 multimode fiber with LC duplex connectors. OM3 is good for up to 70m; OM4 up to 100m at 25G.
What is the difference between 25G and 25GbE? 25G is colloquial; 25GbE (25 Gigabit Ethernet) is the formal standard (IEEE 802.3by). Functionally identical in conversation.
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Pro Disk Network stocks SFP28 transceivers (SR, LR), DAC cables (1m–3m), and 25G server NICs (Mellanox ConnectX-4 Lx, ConnectX-5) — OEM and compatible — with same-day US shipping and Net 30 for verified businesses. Browse networking transceivers or contact us for a 25G migration quote.
Related: Cisco SFP Transceivers Guide · Cisco Catalyst 9200 vs 9300 Comparison