How to Choose 40G QSFP+ Modules

40G QSFP+: A Technology Nearing End of Life but Still Relevant

QSFP+ (Quad SFP+) aggregates 4 10G channels to deliver 40 Gbps. Introduced in 2012, it was the standard for core uplinks and data center spine-leaf networks between 2014 and 2020. In 2026, it is gradually being replaced by 100G QSFP28, which offers a better cost per gigabit (€500 for 100G versus €400 for 40G = €5/Gbps versus €10/Gbps). However, 40G remains widely deployed and relevant in three scenarios: gradual migration of existing infrastructure, 4×10G breakout to increase access-layer density, and budget-constrained deployments.

If you are starting a new DC project in 2026, move directly to 100G QSFP28. If your installed 40G infrastructure is working, there is no need to replace it solely for the sake of upgrading—40G will remain viable for another 5-7 years.

40G QSFP+ Variants

40GBASE-SR4: Multimode for Intra-DC Links

• Reach: 100m over OM3 and 150m over OM4.
• Connector: MPO-12 (12 fibers, 8 used).
• Cisco: QSFP-40G-SR4. OPTINOC price: ~€400 excl. VAT.
• Juniper: JNP-QSFP-40G-SR4. Price: ~€380 excl. VAT.
• Use case: Intra-DC leaf-to-spine links and 40G campus uplinks over multimode fiber.

40GBASE-LR4: Long-Range Single-Mode

• Reach: 10km over OS2 single-mode fiber.
• Connector: Duplex LC (CWDM, 4 wavelengths).
• Cisco: QSFP-40G-LR4. OPTINOC price: ~€2,000 excl. VAT.
• Use case: DCI (Data Center Interconnect) and campus core-to-core links over 100m.

40GBASE-ER4: Extended-Range Single-Mode

• Reach: 40km over OS2 single-mode fiber.
• Cisco: QSFP-40G-ER4. OPTINOC price: ~€3,500 excl. VAT.
• Use case: Metropolitan DCI and service-provider backbones.

QSFP+ to 4× SFP+ Breakout

This is the leading 40G use case in 2026: increasing data center switch density by breaking out one 40G port into 4× 10G connections for 4 servers or 4 pulse links.

• QSFP-4SFP10G-CU1M / CU3M: 1-3m copper DAC breakout cable for intra-rack connections. Price: €150-200 excl. VAT.
• QSFP-4SFP10G-AOC5M / AOC10M: 5-10m AOC breakout cable for inter-rack connections. Price: €300-450 excl. VAT.
• MPO to 4× duplex LC cable: For optical breakout through cassettes. Requires QSFP-40G-SR4 modules and 4× SFP-10G-SR modules.

40G vs. 100G: Making the Decision

• New project in 2026: Move directly to 100G QSFP28. It offers a better cost per Gbps and greater future readiness.
• Expansion of an existing 40G environment: Remain on 40G for compatibility. Nexus 9300 and QFX5110 switches support mixed 40G/100G operation.
• 4×10G breakout: 40G QSFP+ remains relevant and cost-effective for 10G aggregation.
• Gradual migration: Deploy new spine switches at 100G while retaining existing leaf switches at 40G. 100G is backward-compatible with 40G.

OPTINOC Recommendations

40G remains relevant for expanding existing infrastructure and for 4×10G breakout connections. For new deployments, we recommend moving directly to 100G QSFP28—the price difference is minimal (€500 versus €400), while bandwidth is 2.5× higher. OPTINOC supplies genuine Cisco, Juniper, and HPE 40G QSFP+ modules from stock.