QSFP-100G-CU2.5M=: High-Speed Copper Connectivity for Cisco Data Center Ecosystems

​​Overview and Core Functionality​​

The ​​QSFP-100G-CU2.5M=​​ is a 100 Gigabit Ethernet passive direct attach copper (DAC) cable designed for short-range, high-density connections in Cisco data center environments. This 2.5-meter cable terminates with ​​QSFP28 connectors​​, enabling cost-effective 100G links between Cisco Nexus 9000 Series switches, UCS fabric interconnects, and hyperconverged infrastructure. Unlike optical transceivers, it leverages copper’s inherent power efficiency and durability for spine-leaf architectures requiring minimal latency and maximum reliability.

Cisco’s product documentation emphasizes its role in ​​simplifying cable management​​ while reducing total cost of ownership (TCO) compared to active optical cables (AOCs).

​​Technical Specifications and Certifications​​

Key specifications from Cisco’s 100G DAC Design Guide include:

• ​​Data rate​​: 4×25 Gbps NRZ encoding (100G-SR4 and 100G-CR4 standards).
• ​​Cable type​​: 26 AWG twinaxial copper with ​​LSZH (Low Smoke Zero Halogen) jacket​​.
• ​​Maximum reach​​: 3 meters (optimal performance up to 2.5 meters).
• ​​Power consumption​​: 0.8W per end (vs. 3.5W for equivalent QSFP28 optics).
• ​​Compliance​​: IEEE 802.3bj, SFF-8665, RoHS, and REACH.

The cable’s ​​bend radius of 30 mm​​ and ​​snagless boot design​​ prevent damage in congested racks.

​​Primary Use Cases and Deployment Scenarios​​

​​1. Top-of-Rack (ToR) Connectivity​​

Connects ​​Cisco Nexus 93180YC-FX3 switches​​ to:

• ​​UCS B200 M5 blade servers​​ in hyperconverged clusters.
• ​​All-flash storage arrays​​ like NetApp A800 (using Cisco’s SAN Analytics).

​​2. Distributed Disaggregated Chassis (DDC) Architectures​​

Supports leaf-spine interconnects in ​​Cisco Nexus 3232C/3264C systems​​:

• ​​Zero packet loss​​: Verified with Cisco’s Forward Error Correction (FEC) on NX-OS.
• ​​Breakout capability​​: Splits into 4x25G links for gradual upgrades.

​​3. AI/ML Workload Optimization​​

Used in GPU clusters (e.g., NVIDIA DGX A100) to:

• ​​Reduce latency​​: 0.1 μs end-to-end (vs. 0.5 μs for AOCs).
• ​​Support RDMA over Converged Ethernet (RoCEv2)​​.

​​Addressing Critical User Concerns​​

​​Q: Is the QSFP-100G-CU2.5M= compatible with non-Cisco switches?​​

Yes, if the switch supports ​​QSFP28 100G-CR4 mode​​. However, Cisco restricts warranty coverage for third-party hardware interoperability issues.

​​Q: Can it exceed 2.5 meters without signal degradation?​​

While the cable can physically reach 3 meters, testing shows ​​BER (Bit Error Rate) increases by 300%​​ beyond 2.5 meters at 25.78 Gbps.

​​Q: How does heat dissipation compare to AOCs?​​

Passive DACs generate ​​70% less heat​​ than active cables, making them ideal for sealed cabinets. Ensure rack ambient stays ≤35°C (per ASHRAE TC9.9).

​​Q: Are firmware updates required?​​

No. Passive DACs lack firmware, but ensure host devices run ​​NX-OS 9.3(5)+​​ for auto-negotiation and FEC support.

​​Installation and Maintenance Best Practices​​

• ​​Cable dressing​​: Use horizontal managers to avoid sharp bends near connectors.
• ​​Labeling​​: Tag each end with source/destination ports (e.g., “N9K1:1/1 → UCS1:1/2”).
• ​​Pull testing​​: Apply ≤5 lbs force during installation to prevent connector PCB damage.

A common error is ​​mixing DACs with different AWG ratings​​ in the same bundle, causing impedance mismatches and CRC errors.

​​Performance Benchmarks​​

Validation tests on ​​Cisco Nexus 9336C-FX2​​ switches reveal:

• ​​Throughput​​: Sustained 99.999% line rate at 1500B MTU.
• ​​Latency​​: 120 ns per hop (measured via Cisco’s ITD probe).
• ​​Power efficiency​​: 0.02 watts per gigabit (vs. 0.035W for AOCs).

Limitations:

• Not compatible with ​​Cisco 8000 Series routers​​ (requires QSFP-DD cables).
• Avoid ​​parallel runs with 400G DACs​​ due to crosstalk risks.

​​Purchasing and Compatibility Verification​​

Cisco bundles this cable with select Nexus switches, but standalone purchases require validation via ​​Cisco’s Transceiver Module Group (TMG)​​. For guaranteed compatibility and bulk discounts, source from authorized partners like [“QSFP-100G-CU2.5M=” link to (https://itmall.sale/product-category/cisco/).

​​Lessons from Hyperscale Deployments​​

Deploying thousands of these cables in a Meta data center expansion highlighted their reliability—zero field failures over 18 months. However, the lack of polarity reversal forced redesigns in symmetric cabling plans, adding 12 hours per rack. While DACs cut CapEx by 40% versus optics, their weight demands reinforced tray systems. For enterprises adopting ​​Cisco’s Intersight Managed Mode​​, these cables simplify inventory tracking but require strict CMDB hygiene to avoid “phantom port” alerts. In my view, their role in 100G transitions is indispensable, but teams must budget for eventual 400G upgrades—planning pathways to avoid rip-and-replace costs.