QSFP28 100G Buying Guide

QSFP28: the standard 100G module for modern data centers

QSFP28 (Quad SFP28) has been the dominant 100 Gigabit Ethernet transceiver form factor since 2018. It aggregates 4 channels of 25G NRZ to deliver 100 Gbps in a compact QSFP form factor. It is the standard module for spine-leaf uplinks, DCI (Data Center Interconnect), and high-performance server connections. In 2026, QSFP28 remains the price/performance sweet spot for enterprise data centers—400G QSFP-DD is taking over for hyperscalers and new builds, but 80% of deployed fabrics still run at 100G.

The QSFP28 market is mature: prices have fallen by 60% in 3 years. A genuine Cisco QSFP-100G-SR4-S now costs approximately €500 excluding VAT from OPTINOC, compared with approximately €1,200 in 2021. Now is the time to invest.

QSFP28 100G variants by reach

100GBASE-SR4: the intra-data-center standard

SR4 uses 4 channels of 25G over multimode fiber (850nm) with an MPO-12 connector. It is the most widely deployed data center module for short-distance leaf-spine links.

• Reach: 70m over OM3, 100m over OM4. Sufficient for 99% of intra-DC use cases.
• Connector: MPO-12 (Multi-fiber Push-On, 12 fibers, 8 of which are used).
• Cisco: QSFP-100G-SR4-S. OPTINOC price: approximately €500 excluding VAT.
• Juniper: JNP-QSFP-100G-SR4. Price: approximately €450 excluding VAT.
• Aruba: R0Z21A (100G SR4). Price: approximately €480 excluding VAT.
• Breakout: MPO-12 → 4× LC duplex cable for connecting 4 SFP28 25G servers to 1 QSFP28 100G port. Saves 3 switch ports.
• Use cases: intra-room leaf ↔ spine links and leaf ↔ server 100G NIC connections (Mellanox ConnectX-6).

100GBASE-LR4: campus and short-distance DCI

LR4 uses 4 CWDM wavelengths over a single-mode fiber pair (LC duplex). Its 10km reach makes it suitable for extended campuses and intra-metro DCI.

• Reach: 10km over OS2 single-mode fiber.
• Connector: LC duplex (2 fibers, no MPO).
• Cisco: QSFP-100G-LR4-S. OPTINOC price: approximately €2,800 excluding VAT.
• Juniper: JNP-QSFP-100G-LR4. Price: approximately €2,500 excluding VAT.
• Use cases: DCI between 2 data centers located 1-10km apart, 100G campus core, and leased-fiber interconnection.
• Caution: the LR4 loss budget is tight (approximately 6 dB). For fiber with many splices (>8), perform an OTDR test before ordering.

100GBASE-CWDM4: a cost-effective LR4 alternative

CWDM4 is a cost-effective LR4 variant with a reduced reach of 2km. It uses the same 4-wavelength CWDM technology over LC duplex, but less powerful laser components reduce the price by 40-50% compared with LR4.

• Reach: 2km over OS2 single-mode fiber.
• Cisco: QSFP-100G-CWDM4-S. OPTINOC price: approximately €1,400 excluding VAT.
• Use cases: DCI between 2 nearby buildings (<2km) and inter-building campus core links. If your distance is <2km, CWDM4 saves €1,400 per module compared with LR4.

100GBASE-PSM4: 500m parallel single-mode connectivity

PSM4 uses 4 parallel single-mode fibers (MPO-12, like SR4, but over SMF). Its 500m reach bridges the gap between SR4 (100m maximum) and LR4 (10km). It is ideal for data center campuses with inter-building distances of 100-500m.

• Reach: 500m over OS2 single-mode fiber.
• Connector: MPO-12.
• Cisco: QSFP-100G-PSM4-S. OPTINOC price: approximately €800 excluding VAT.
• Use cases: inter-building DCI over 100-500m using existing single-mode fiber. More cost-effective than LR4 when the distance allows.

100GBASE-ZR4: coherent long-distance connectivity

ZR4 uses coherent modulation to achieve 80km over single-mode fiber. It is the pluggable version of WDM systems, replacing a dedicated transponder in an optical chassis.

• Reach: 80km over OS2 single-mode fiber with EDFA amplification.
• Cisco: QSFP-100G-ZR4-S. OPTINOC price: approximately €7,000 excluding VAT.
• Use cases: long-distance DCI (inter-city) and carrier backbones. Replaces dedicated WDM systems, saving approximately 50% compared with a complete WDM solution.

QSFP28 → 4× SFP28 25G breakout

Breakout is the most widely deployed architecture in spine-leaf data centers. A QSFP28 100G port on the spine is split into 4× 25G SFP28 connections to 4 different servers. This maximizes density: a 32× 100G spine can connect 128 servers using breakout connections.

• Active breakout cable: QSFP-4SFP25G-CU3M (Cisco)—QSFP28 → 4× SFP28 copper DAC, 3m. Price: approximately €200 excluding VAT.
• Optical breakout cable: QSFP-100G-AOC-4×25G-10M—fiber AOC, 10m. Price: approximately €400 excluding VAT.
• MPO → 4× LC breakout: MPO-12 cassette to 4 LC duplex patch cords. For distances >10m over fiber. Cassette price: approximately €150.
• Switch configuration: breakout interface on Nexus (interface breakout module X port Y map 25g-4x) or QFX (set chassis fpc X pic Y port Z channel-speed 25g).

100G fabric sizing

Small DC (4-8 racks, 50-200 servers)

• 4-8 leaf switches (Nexus 93180YC-FX or QFX5120-48Y): 6-8 100G uplinks each.
• 2 spine switches (Nexus 9336C-FX2 or QFX5120-32C): 32× 100G.
• Modules: approximately 20-30 QSFP28 SR4 (leaf↔spine) + approximately 200 SFP28 25G (leaf↔server via breakout or direct connections).
• Optics budget: approximately €15-25K excluding VAT.

Medium-sized DC (8-32 racks, 200-1000 servers)

• 16-32 leaf switches + 4-6 spine switches.
• Modules: approximately 100-150 QSFP28 SR4 + approximately 600-1000 SFP28 25G.
• Optics budget: approximately €80-120K excluding VAT.
• DCI (for multi-DC environments): 4-8 QSFP28 LR4 or CWDM4 modules for interconnection.

Genuine vs. compatible QSFP28 modules

QSFP28 is the module category where the appeal of compatible products is strongest—the volumes are high and the price difference is significant. A compatible QSFP-100G-SR4 costs approximately €150, compared with approximately €500 for a genuine module. Across 100 modules, that represents savings of €35K.

Our field-based recommendation: Premium-compatible modules (Flexoptix, ProLabs) are acceptable for non-critical intra-DC links in development, staging, and lab environments. Genuine modules are mandatory for production links covered by SmartNet/JTAC contracts. An incident on a spine uplink using a compatible module means TAC may reject the support ticket, leaving you to resolve the issue alone at 3 a.m.

Order from OPTINOC

OPTINOC supplies genuine, manufacturer-warranted QSFP28 100G modules from Cisco, Juniper, HPE Aruba, Palo Alto, Fortinet, and Extreme. European stock with delivery in 24-72h. Volume discounts are available from 10 modules. Request a quote with your exact quantities for each part number.