Do these 3 things before closing this tab:
1Fix the driver behind crashes, sound loss and screen glitches2Repair Windows errors before they cause bigger problems3Scan for outdated or missing drivers - takes under a minute40 Gigabit Ethernet (40GbE) is Ethernet operating at a nominal link rate of 40 gigabits per second (40 Gb/s). It describes the link speed, not a particular cable: the physical-layer type determines which medium, transceiver, connector, and distance are supported.
What does 40GbE mean?
40GbE is a high-speed Ethernet connection that carries Ethernet frames at a nominal rate of 40 Gb/s. IEEE 802.3ba-2010 added specifications for Ethernet at 40 Gb/s and 100 Gb/s, including MAC parameters, physical layers, and management parameters. The amendment was published on June 22, 2010, and IEEE now marks it as superseded. Its technical contribution is incorporated into the broader IEEE 802.3 standard family; IEEE 802.3-2022 describes Ethernet across selected speeds from 1 Mb/s through 400 Gb/s.
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These standards describe Ethernet operation and interfaces, not one universal 40GbE cable. The physical-layer implementation—often called a PHY—sets the link’s medium and practical reach.
What are the common 40GbE interface types?
The names below identify different physical-layer approaches. They are examples, not an exhaustive list of vendor implementations.
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| Interface | Medium and example implementation | Reach context |
|---|---|---|
| 40GBASE-SR4 | Multimode fiber; four-lane optics. Cisco describes a 850 nm module with an MPO-12 connector. | At least 100 m in the Fiber Optics Tech Consortium overview; supported distance depends on fiber grade and the specific equipment. |
| 40GBASE-LR4 | Single-mode fiber; four wavelength lanes multiplexed in the module. Cisco’s cited module uses duplex LC. | Up to 10 km in the cited overview and Cisco module description. |
| 40GBASE-CR4 | Twinax copper direct-attach cable. | Up to 7 m in the cited overview. |
These figures describe the cited interface examples; they are not guarantees for every installation. Fiber grade, link budget, module specifications, and support at both ends can affect whether a particular link works at its intended distance. Cisco also documents other 40G options, including bidirectional multimode modules and active optical cables.
How do you choose a 40GbE cable or transceiver?
A 40G QSFP+ transceiver is one product category used for 40GbE optical links, but the label alone does not establish compatibility. Match the exact module and cable to the equipment and route.
- Check the ports at both ends. Confirm that each switch or router supports the exact transceiver or cable model. Cisco’s documentation covers a product-specific module range and identifies interoperability where applicable; support should not be assumed across all devices.
- Choose the medium for the route. Select multimode fiber for a compatible SR4 link, single-mode fiber for a compatible LR4 link, or twinax copper for a compatible CR4 direct-attach connection.
- Match the connector and lane implementation. For example, the cited Cisco SR4 module uses MPO-12, while its LR4 example uses duplex LC. Confirm the connector and required cabling for the exact SKU.
- Verify distance and cable specifications. Check the module’s stated reach, installed fiber grade or copper cable specification, and link budget. Do not treat reach figures for one PHY as applying to another.
Where is 40GbE used?
Cisco describes its 40G QSFP portfolio for data centers, high-performance computing networks, enterprise core and distribution layers, and service-provider applications. These are vendor-stated application contexts; they do not establish how widely 40GbE is deployed or whether it is the right speed for a particular network.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What is the status of IEEE 802.3ba-2010?
IEEE 802.3ba-2010 was the amendment that introduced 40 Gb/s and 100 Gb/s Ethernet specifications. The IEEE task-force history says the work concluded with approval at the June 2010 IEEE Standards Board meeting. IEEE lists the amendment as superseded, so it is more accurate to describe 40GbE as part of the IEEE 802.3 family than as governed by a current standalone 802.3ba standard.
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