What is CVR-QSFP28-SFP25G=?, Purpose, Compatibility, and Use Cases for Cisco Breakout Cabling

​​Core Functionality: 100G to 4x25G Breakout Solution​​

The ​​CVR-QSFP28-SFP25G=​​ is a ​​passive breakout cable​​ designed to split a single ​​100G QSFP28 port​​ into four independent ​​25G SFP28 connections​​. This cost-effective solution optimizes port density in Cisco data center switches, enabling flexible connectivity for scenarios requiring mixed-speed uplinks.

Key specifications include:

• ​​Cable type​​: ​​Copper Direct Attach Cable (DAC)​​ with a maximum reach of ​​3 meters​​ (no signal amplification).
• ​​Protocol support​​: Ethernet (25GBASE-CR) and Fibre Channel over Ethernet (FCoE).
• ​​Power efficiency​​: 0.1W per lane, reducing thermal load in high-density chassis.

​​Compatibility and Supported Platforms​​

This cable is engineered for Cisco’s ​​Nexus 9000 series​​ and ​​UCS 6400 Series Fabric Interconnects​​, specifically:

• ​​Nexus 93180YC-FX​​: Converts 100G ports to 25G for legacy server connections.
• ​​Nexus 9336C-FX2​​: Aggregates 25G storage traffic (e.g., NetApp AFF arrays).
• ​​UCS 6454 Fabric Interconnect​​: Links to 25G NICs in UCS B200 M5 blade servers.

​​Typical Deployment Scenarios​​

​​1. Hybrid Cloud Data Centers​​

Connect 100G spine switches to 25G leaf switches or hyperconverged nodes (e.g., Cisco HyperFlex).

​​2. Storage Area Networks (SAN)​​

Bridge QSFP28-equipped switches to 25G iSCSI/NVMe storage systems like Pure Storage FlashArray.

​​3. AI/ML Workloads​​

Cost-effective interconnect for GPU clusters requiring low-latency 25G links between training nodes.

​​Critical User Questions Addressed​​

​​Q: Does it support auto-negotiation for 10G/40G speeds?​​

A: ​​No​​. The cable is hard-coded for 25G per lane. For 10G, use ​​QSFP-40G-SR4​​ with SFP+ adapters.

​​Q: Is it compatible with third-party switches like Arista?​​

A: Limited. While physically compatible, Cisco’s firmware often blocks non-Cisco coded DACs.

​​Q: Can it be used for breakout to 50G?​​

A: No. For 2x50G splits, opt for ​​QSFP-100G-AOC2​​ active optical cables.

​​Procurement and End-of-Life Considerations​​

Cisco has shifted focus to active optical cables (AOCs) for longer reaches, but the CVR-QSFP28-SFP25G= remains available via ​​itmall.sale​​ for enterprises prioritizing cost over distance.

Key purchasing tips:

• Verify ​​Cisco SKU validation​​ to avoid counterfeit cables.
• Check ​​DOM support​​ if real-time diagnostics are required (this DAC lacks DOM).
• Inspect ​​QSFP28 connector latches​​ for wear—refurbished units may have weakened retention.

​​Strategic Perspective: Balancing Cost and Future-Proofing​​

In a recent data center consolidation project, the CVR-QSFP28-SFP25G= saved ~60% compared to optical alternatives for under-3m server-to-leaf links. However, its lack of flexibility for higher speeds or longer distances makes it a tactical choice, not a strategic one.

With 400G adoption accelerating, I recommend reserving this cable for edge/retrofit scenarios. For core layers, invest in ​​QSFP-DD-400G-SR8​​ optics to accommodate future AI-driven traffic spikes. The CVR-QSFP28-SFP25G= excels in bridging today’s 25G needs with legacy 100G investments—but only if your roadmap doesn’t include 50G/100G server upgrades within 18 months.