Enterprise Resource Center • Networking
100GbE 100 Gigabit Ethernet Explained
Understand 100 Gigabit Ethernet, including QSFP28 transceivers, DAC and AOC cables, 100GBASE-SR4 and LR4 fiber, MPO and LC connectivity, forward error correction, 4x25GbE breakout and modern data-center architectures.
100 Gb/s QSFP28 100GBASE-SR4 100GBASE-LR4 MPO / LC 4x25GbE Breakout
High-Speed Ethernet
What Is 100GbE?
100GbE, or 100 Gigabit Ethernet, is a family of Ethernet technologies providing a nominal aggregate data rate of 100 gigabits per second.
100GbE is widely deployed for data-center switch uplinks, leaf-and-spine fabrics, aggregation, storage networks, high-performance computing and other bandwidth-intensive enterprise applications.
The QSFP28 form factor became one of the most important interfaces for 100GbE. Many QSFP28 implementations combine four 25Gb/s electrical lanes to create a 100Gb/s Ethernet connection.
100GbE Quick Reference
100 Gigabit Ethernet at a Glance
100 Gb/s
Nominal Link Rate Four times the nominal bandwidth of 25GbE.
QSFP28
Common Form Factor Widely deployed for 100GbE optical and copper links.
4x25G
Classic Lane Architecture Many QSFP28 systems use four 25Gb/s electrical lanes.
4x25GbE
Breakout Capability Supported ports can connect four independent 25GbE endpoints.
100GbE Form Factor
100GbE and QSFP28
QSFP28 stands for Quad Small Form-factor Pluggable 28. It uses four high-speed lanes and is widely associated with 100 Gigabit Ethernet.
QSFP28 ports can support multiple physical media depending on the host platform, including optical transceivers, Direct Attach Copper cables and Active Optical Cables.
QSFP28 DAC Short copper connections.
QSFP28 AOC Integrated optical cabling.
QSFP28 SR4 Parallel multimode fiber.
QSFP28 LR4 Long-reach single-mode fiber.
100 Gigabit Ethernet Interfaces
Common 100GbE Connection Types
| Connection |
Medium |
Connector / Interface |
Common Application |
| QSFP28 DAC |
Twinax copper |
Fixed QSFP28 |
Short rack-level links |
| QSFP28 AOC |
Integrated optical fiber |
Fixed QSFP28 |
Rack and row connectivity |
| 100GBASE-SR4 |
Multimode fiber |
MPO/MTP |
Short-reach data-center fiber |
| 100GBASE-LR4 |
Single-mode fiber |
Duplex LC |
Long-reach enterprise links |
| CWDM4 / PSM4 |
Single-mode fiber |
Varies by optical implementation |
Data-center interconnect |
Parallel Multimode Fiber
What Is 100GBASE-SR4?
100GBASE-SR4 is a short-reach 100GbE optical standard designed for multimode fiber. It uses parallel optical transmission rather than sending the entire 100Gb/s connection over one optical pair.
SR4 commonly uses an MPO/MTP multifiber connector and laser-optimized multimode fiber. This makes fiber type, polarity and MPO/MTP pinning important considerations when deploying SR4 links.
Single-Mode Fiber
What Is 100GBASE-LR4?
100GBASE-LR4 is a long-reach 100GbE optical standard designed for single-mode fiber.
Unlike SR4's parallel multimode architecture, LR4 uses wavelength-division multiplexing to carry multiple optical wavelengths across a duplex single-mode fiber pair. QSFP28 LR4 modules therefore commonly use duplex LC connectivity.
Fiber Connectivity
MPO/MTP vs. LC for 100GbE
| Feature |
MPO / MTP |
Duplex LC |
| Fiber Architecture |
Parallel fiber |
Duplex fiber pair |
| Typical 100GbE Example |
100GBASE-SR4 |
100GBASE-LR4 |
| Common Fiber |
Multimode |
Single-mode for LR4 |
| Important Consideration |
Polarity, fiber count and pinning |
TX/RX polarity and fiber type |
Short-Reach Connectivity
100GbE DAC vs. AOC vs. Optical Transceivers
QSFP28 DAC
Direct Attach Copper provides a fixed-length Twinax connection and is commonly used for short links within or between nearby racks.
QSFP28 AOC
Active Optical Cable integrates optical components and fiber into a factory-terminated cable assembly.
QSFP28 Optics
Removable optical transceivers provide greater flexibility for structured fiber cabling and longer-distance network designs.
Breakout Networking
100GbE to 4x25GbE Breakout
Many QSFP28 switch interfaces are based on four 25Gb/s electrical lanes. On supported hardware, those lanes can be separated to create four individual 25GbE interfaces.
100GbE QSFP28 → 4 × 25GbE SFP28
Breakout can be implemented using compatible QSFP28-to-4xSFP28 DAC assemblies, AOCs or optical breakout architectures. The switch must explicitly support breakout operation on the selected port.
Signal Integrity
Forward Error Correction in 100GbE
Forward Error Correction (FEC) allows a receiver to detect and correct certain transmission errors by adding redundant information to the data stream.
FEC is important in high-speed Ethernet because higher signaling rates reduce the available signal margin. The required FEC mode depends on the Ethernet physical layer, host hardware, transceiver and cabling implementation.
Compatibility Warning A FEC mismatch can prevent a 100GbE link from establishing even when the cable or transceivers appear physically compatible.
Network Architecture
25GbE vs. 100GbE
| Feature |
25GbE |
100GbE |
| Nominal Rate |
25 Gb/s |
100 Gb/s |
| Common Form Factor |
SFP28 |
QSFP28 |
| Common Data-Center Role |
Server access |
Uplink, aggregation and fabric |
| Classic Lane Structure |
1x25G |
4x25G |
| Breakout Relationship |
Breakout endpoint |
Can provide 4x25GbE when supported |
Data Center Architecture
100GbE in Leaf-and-Spine Networks
Server Access
Servers may connect to leaf switches using 10GbE or 25GbE interfaces depending on workload requirements.
Leaf Uplinks
100GbE provides substantially more aggregate capacity for traffic leaving server-facing leaf switches.
Spine Fabric
100GbE links can form the high-bandwidth fabric between leaf and spine switching layers.
Enterprise Applications
Where Is 100GbE Used?
Data Center Uplinks High-bandwidth connectivity between switching tiers.
Leaf-Spine Fabrics High-capacity east-west traffic transport.
Storage Networks High-throughput storage and distributed data platforms.
HPC Clusters Bandwidth-intensive compute and research environments.
Cloud Infrastructure Large-scale virtualization and distributed applications.
25GbE Aggregation Aggregating multiple high-speed server connections.
Compatibility Checklist
What Should You Check Before Buying 100GbE Hardware?
1. Port Type Confirm QSFP28 and supported operating modes.
2. Ethernet Standard Match SR4, LR4 or other required physical layer.
3. Fiber Type Confirm multimode or single-mode requirements.
4. Connector Verify MPO/MTP, duplex LC or fixed cable interface.
5. Reach Choose media appropriate for the required distance.
6. FEC Confirm compatible FEC requirements at both endpoints.
7. Transceiver Coding Verify vendor and platform support.
8. Breakout Support Confirm 4x25GbE mode when breakout is required.
Troubleshooting
Why Is My 100GbE Link Not Working?
Unsupported QSFP28
The switch or adapter may reject an unsupported module or cable.
Wrong Fiber Type
SR4 and LR4 use different fiber architectures.
MPO Polarity
Parallel optics require the correct fiber polarity and pinning.
FEC Mismatch
Both endpoints must use compatible FEC settings.
Breakout Configuration
A 100GbE port may require explicit configuration before operating as 4x25GbE.
Dirty Optical Connectors
Contamination can introduce optical loss and prevent reliable link operation.
Frequently Asked Questions
100GbE FAQ
What does 100GbE mean?
100GbE means 100 Gigabit Ethernet, a family of Ethernet technologies providing a nominal aggregate data rate of 100 gigabits per second.
What is QSFP28?
QSFP28 is a four-lane pluggable interface widely used for 100GbE transceivers, Direct Attach Copper cables and Active Optical Cables.
What is 100GBASE-SR4?
100GBASE-SR4 is a short-reach 100GbE optical standard using parallel multimode fiber and commonly an MPO/MTP multifiber interface.
What is 100GBASE-LR4?
100GBASE-LR4 is a long-reach 100GbE standard using single-mode fiber and wavelength-division multiplexing. QSFP28 LR4 modules commonly use duplex LC connectors.
Does 100GbE use LC or MPO?
It can use either depending on the optical standard. 100GBASE-SR4 commonly uses MPO/MTP parallel fiber, while 100GBASE-LR4 commonly uses duplex LC single-mode fiber.
Can 100GbE use DAC cables?
Yes. QSFP28 Direct Attach Copper cables are commonly used for short 100GbE connections where the switch and endpoint support the selected cable.
Can QSFP28 break out to four SFP28 ports?
Yes. Many compatible QSFP28 switch ports support breakout into four independent 25GbE SFP28 connections. The port, switch software and breakout media must support this operating mode.
Is 100GbE four times faster than 25GbE?
At the nominal Ethernet link-rate level, 100GbE provides four times the aggregate bandwidth of 25GbE: 100 Gb/s compared with 25 Gb/s.
Where is 100GbE commonly used?
100GbE is commonly used for data-center uplinks, leaf-and-spine fabrics, network aggregation, storage networks, high-performance computing and other high-bandwidth infrastructure.
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