800G-to-Eight 100G Links for Switch-to-Switch Connectivity

800G-to-Eight 100G Links for Switch-to-Switch Connectivity

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800G-to-Eight 100G Links for Switch-to-Switch Connectivity

Introduction

As data centers scale to support AI, HPC, and cloud workloads, high-bandwidth interconnects between switches become critical. One common scenario is connecting an 800G Ethernet switch (e.g., NVIDIA Spectrum-4) to multiple 100G Ethernet switches using breakout configurations. This article explores how OSFP-DR8-800G transceivers enable 800G-to-8x100G connectivity, optimizing network efficiency and cost.

800G-to-Eight 100G Links for Switch-to-Switch Connectivity

1. Why Use 800G-to-8x100G Breakout?

Key Benefits

✔ Maximize Port Utilization – A single 800G port can replace eight 100G ports, reducing switch density requirements.
✔ Cost Efficiency – Fewer high-speed transceivers and cables compared to multiple 100G links.
✔ Future-Proofing – 800G switches (like Spectrum-4) can support legacy 100G devices while preparing for future upgrades.

Use Cases

  • AI/ML Clusters – Connecting GPU nodes with mixed-speed networking.

  • Cloud Data Centers – Aggregating multiple 100G leaf switches into an 800G spine.

  • Storage Networks – High-throughput links between storage arrays and compute nodes.

2. Hardware Requirements

A. 800G Switch: NVIDIA Spectrum-4

  • Port Speed: 800G (OSFP)

  • Breakout Support: 8x100G (via OSFP-DR8)

  • Key Features:

    • Adaptive Routing & RoCEv2 support

    • 25.6Tbps switching capacity

    • Low-latency cut-through forwarding

B. Transceiver: OSFP-DR8-800G

Parameter Details
Form Factor OSFP
Breakout Mode 8x100G (DR8)
Max Distance 500m (SMF)
Power Consumption <14W
Compatibility Spectrum-4, Spectrum-3

C. Cabling Options

  1. OSFP-DR8 to 8x100G DAC/AOC

    • Short-reach (<5m), low-latency, cost-effective

  2. OSFP-DR8 to 8xLC Fiber Patch Panel

    • Longer distances (up to 500m) using MTP-to-LC breakout cables

3. Configuration Steps

Step 1: Enable Breakout Mode on Spectrum-4

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# Set port 1/1 to 8x100G breakout
sudo mlxconfig -d /dev/mst/mt4123_pciconf0 set LINK_TYPE_P1=8x100G

Note: Reboot required for changes to take effect.

Step 2: Verify Link Status

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sudo ethtool --show-module sw1p1
# Expected output:
# Lanes: 8x100G
# Status: Active

Step 3: Configure LAG (Optional)

For redundancy, bundle multiple 100G links into a LAG:

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sudo teamdctl lag0 create
sudo teamdctl lag0 addport sw1p1s0
sudo teamdctl lag0 addport sw1p1s1
...

4. Performance Considerations

Latency

  • 800G Native: ~300ns (Spectrum-4 cut-through mode)

  • 8x100G Breakout: ~350ns (due to gearbox overhead)

Power Efficiency

Configuration Power per 800G Equivalent
1x OSFP-DR8 14W
8x 100G-SFP56 32W

5. Comparison to Alternatives

Approach Pros Cons
800G-to-8x100G Saves switch ports Limited to 500m distance
Native 100G Longer reach (>2km) Higher cabling cost
400G-to-4x100G Wider compatibility Half bandwidth density

6. Troubleshooting Tips

❌ Link Flapping → Check fiber polarity (DR8 uses MPO-16)
❌ Low Throughput → Verify ethtool reports "8x100G" mode
❌ High BER → Replace faulty breakout cable

Conclusion

Deploying 800G-to-8x100G links with NVIDIA Spectrum-4 and OSFP-DR8 transceivers optimizes data center scalability. This approach balances:

  • ✅ Bandwidth density (1:8 port consolidation)

  • ✅ Power efficiency (56% lower power than 8x100G)

  • ✅ Future readiness (Easy upgrade to native 800G)

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