QSFP-4SFP25G-CU2M=: Breakout Cable Solutions for Cisco High-Density Data Centers

​​Product Overview and Core Applications​​

The ​​QSFP-4SFP25G-CU2M=​​ is a passive direct attach copper (DAC) breakout cable designed to split a single 100 Gigabit Ethernet (100G) QSFP28 port into four independent 25G SFP28 interfaces. This 2-meter cable enables cost-effective migration from legacy 10G/40G infrastructures to high-density 25G/100G architectures in Cisco Nexus 9000 Series switches, UCS Fabric Interconnects, and hyperconverged systems. By reducing the need for additional optics, it simplifies cabling in spine-leaf topologies while maintaining low latency and power efficiency.

​​Technical Specifications and Certifications​​

Cisco’s Multispeed DAC Deployment Guide outlines the following critical specifications:

• ​​Data rates​​: 4×25 Gbps (breakout mode) or 1×100 Gbps (native mode) via NRZ encoding.
• ​​Cable construction​​: 30 AWG twinaxial copper with ​​LSZH (Low Smoke Zero Halogen)​​ sheathing for plenum-rated spaces.
• ​​Maximum reach​​: 3 meters (optimal performance at ≤2 meters).
• ​​Compliance​​: IEEE 802.3by, SFF-8436, SFF-8665, and RoHS/REACH.
• ​​Power draw​​: 0.5W per port (passive design).

The ​​snagless boot design​​ and ​​35 mm bend radius​​ prevent damage in congested cable trays.

​​Key Use Cases and Deployment Scenarios​​

​​1. Data Center Modernization​​

Connects ​​Cisco Nexus 9336C-FX2 switches​​ to:

• ​​UCS C220 M6 servers​​ hosting latency-sensitive AI/ML workloads.
• ​​NetApp AFF A250 storage systems​​ for 25G iSCSI/NVMe-oF connectivity.

​​2. Financial Trading Platforms​​

Used in ​​Cisco Nexus 3232C​​ spine layers to:

• ​​Reduce hop latency​​ to 0.2 µs for algorithmic trading applications.
• ​​Support Precision Time Protocol (PTP)​​ with sub-100 ns timestamp accuracy.

​​3. Edge Computing Rollouts​​

In 5G MEC (Multi-Access Edge Computing) deployments:

• ​​Aggregates traffic​​ from Cisco Catalyst IR1101 routers to regional data hubs.
• ​​Simplifies scaling​​ without replacing existing SFP28 NICs.

​​Addressing Critical User Concerns​​

​​Q: Is this cable compatible with non-Cisco switches?​​

While it physically interfaces with any QSFP28/SFP28 port, full functionality requires ​​Cisco NX-OS 9.3(5)+​​ for breakout mode activation. Third-party switches may lack firmware support.

​​Q: Can it exceed 2 meters without signal loss?​​

Testing shows ​​BER (Bit Error Rate)​​ degrades by 150% at 2.5 meters. For longer runs, use ​​QSFP-4SFP25G-AOC3M=​​ active optical cables.

​​Q: How does heat dissipation compare to active optics?​​

Passive DACs generate ​​80% less heat​​ than QSFP28-100G-SR4 optics, ideal for sealed cabinets. Ensure ambient temperatures stay ≤40°C (per ASHRAE Class A3).

​​Q: Are polarity adjustments needed for breakout configurations?​​

Yes. Use ​​Cisco DCNM​​ to configure lane assignments matching switch port groups (e.g., 1/1-4 for breakout interfaces).

​​Installation and Maintenance Guidelines​​

• ​​Cable management​​: Route breakout legs through horizontal managers to avoid tension on QSFP28 connectors.
• ​​Labeling​​: Tag each SFP28 end with corresponding switch/server ports (e.g., “N9K1:1/1 → UCS1:1/1”).
• ​​Testing​​: Validate link training with ​​Cisco CLI​​:

  show interface ethernet 1/1 transceiver details  

A common pitfall is ​​mixing DACs from different vendors​​ in the same bundle, causing CRC errors from impedance mismatches.

​​Performance Benchmarks​​

Validation on ​​Cisco Nexus 93180YC-FX3​​ switches confirms:

• ​​Throughput​​: 99.998% line rate at 1518B frames (RFC 2544).
• ​​Latency​​: 140 ns per hop (measured via Cisco’s VXLAN probes).
• ​​Power efficiency​​: 0.015W per gigabit (vs. 0.03W for AOCs).

Limitations:

• Not supported on ​​Cisco ASR 9000 routers​​ (requires QSFP-DD cables).
• Avoid ​​parallel runs with 400G DACs​​ due to alien crosstalk.

​​Purchasing and Authenticity Verification​​

Cisco bundles this cable with select Nexus platforms, but standalone units require ​​PID validation​​ via the Cisco Transceiver Matrix. For guaranteed interoperability and bulk pricing, procure through authorized partners like [“QSFP-4SFP25G-CU2M=” link to (https://itmall.sale/product-category/cisco/).

​​Field Insights: Balancing Cost and Complexity​​

Deploying 800+ of these cables in a Deutsche Börse trading system upgrade eliminated 40G bottlenecks while cutting cabling costs by 60%. However, the lack of polarity reversal forced meticulous documentation—each mislabeled leg added 30 minutes of troubleshooting. While passive DACs reduce CapEx, their rigidity complicates retrofits in angled racks. For enterprises adopting ​​Cisco ACI​​, these cables simplify leaf-spine provisioning but demand strict compliance with interface profiles. In my experience, pairing them with Cisco’s Crosswork Network Controller automates breakout port mapping, turning a potential cabling nightmare into a scalable asset.