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As data center infrastructure evolves, network engineers often need to connect high-bandwidth switching equipment with servers and network devices that operate at different speeds. A direct attach copper cable with a breakout configuration can help bridge this gap without requiring every connected device to use the same port type.

The DAC 100Gb/s cable offered by Infinol is available in configurations that include QSFP28-to-QSFP28 and QSFP28-to-four-SFP28 connections. For compatible equipment, the breakout version allows one 100G QSFP28 interface to connect to four separate 25G SFP28 interfaces. Before deployment, however, engineers should verify port capabilities, cable specifications, lane mapping, and the network configuration to ensure that the selected assembly meets the intended application.

Understanding the 100G QSFP28-to-4×25G Breakout Design

A QSFP28-to-four-SFP28 direct attach copper cable has one QSFP28 connector at the source end and four SFP28 connectors at the destination end. The QSFP28 side connects to a compatible 100G port, while the four branches connect to supported 25G interfaces.

The design combines four nominal 25Gb/s lanes to provide an aggregate data rate of approximately 100Gb/s. Infinol lists a maximum data rate of 103.1Gb/s for the relevant 100G DAC product family.

Unlike optical fiber assemblies, DAC cables use twinax copper conductors for short-distance connectivity. They can be a practical choice for connections between equipment located within the same rack or in nearby rack positions, provided the selected cable length and host interfaces support the required link.

It is important to distinguish a standard QSFP28-to-QSFP28 cable from a breakout assembly. The former connects two QSFP28 ports, while the latter distributes a compatible high-speed interface across four SFP28 connections. The cable itself does not automatically convert every 100G port into four independent 25G links. The switch or host device must support the appropriate breakout mode, and its configuration must enable the intended interfaces.

Common Applications for 100G DAC Breakout Cables

Breakout cabling is useful when the interface on a switch does not directly match the interfaces required by connected devices. Several data center layouts may benefit from this arrangement.

Connecting multiple 25G servers to a 100G switch

A compatible 100G switch port can provide physical connections to four 25G server interfaces through a breakout cable. This arrangement may help simplify cabling in a rack where the switch supports four-way breakout and the network design allows each branch to operate as intended.

Supporting storage and aggregation networks

Storage platforms and network appliances may use 25G interfaces while the aggregation layer provides 100G ports. A breakout assembly can support these connections without requiring every endpoint to upgrade to 100G immediately.

Planning phased network upgrades

Some facilities introduce higher-speed switches before replacing all connected servers and network adapters. A 100G-to-four-25G cable can help connect compatible legacy-speed endpoints to newer switching infrastructure, subject to the supported port modes and network topology.

The best configuration depends on traffic distribution, redundancy requirements, switch capabilities, and the intended role of each connection. Engineers should confirm that the proposed breakout design meets the actual network requirements rather than assuming that connector compatibility guarantees operational support.

Organizing Port Mapping Before Deployment

A breakout cable creates several physical links from one source port, so documenting the connections before installation can simplify setup and future maintenance.

Start by identifying the source switch, its QSFP28 port number, and the four destination devices. Record the SFP28 port assigned to each branch, along with the intended link speed and network purpose.

A basic planning table can use the following structure:

Source interface	Destination interface	Intended connection
Switch A, QSFP28 port 1	Server A, SFP28 port 1	25G link
Switch A, QSFP28 port 1	Server B, SFP28 port 1	25G link
Switch A, QSFP28 port 1	Server C, SFP28 port 1	25G link
Switch A, QSFP28 port 1	Server D, SFP28 port 1	25G link

This is an illustrative example, not a universal port assignment. Port numbering and lane-to-interface mapping vary by switch platform. Consult the relevant hardware documentation to determine how the breakout interfaces are identified and configured.

Clear labels on both ends of each branch can also reduce confusion when multiple cables are installed in a high-density rack. A documented mapping plan makes it easier to trace connections, replace components, and isolate faults during maintenance.

Selecting an Appropriate Cable Length

Cable length influences routing flexibility, rack organization, and ease of servicing. Infinol lists 1m, 2m, 3m, and 5m options for its standard QSFP28 DAC and QSFP28-to-four-SFP28 breakout cable configurations.

A 1m assembly may suit devices positioned close together. A 2m or 3m cable can provide additional routing flexibility when equipment occupies different positions in a rack. A 5m version may accommodate longer paths within a supported short-distance copper deployment, provided the specific cable and connected devices meet the required operating specifications.

Measure the complete cable route rather than estimating length from the straight-line distance between ports. Account for horizontal and vertical cable managers, the position of the connectors, routing bends, and the slack needed to access equipment during servicing.

Breakout assemblies require additional attention because the four SFP28 branches may connect to different devices or port locations. Check the branch arrangement and physical reach before ordering. The precise construction and available options should be verified against the datasheet for the selected part number.

Choosing a suitable length can help avoid excess cable clutter while preventing tension on connectors and unnecessary strain on the assembly.

Checking QSFP28 and SFP28 Compatibility

Matching connector types is only the first step in selecting a suitable DAC. The source device must support 100G operation and the intended breakout mode, while each destination port must support the required 25G connection.

Infinol identifies its 100G DAC products with references to QSFP28 MSA, IEEE 802.3, and SFF-8665 specifications. The product information also references transmission requirements associated with 100 Gigabit Ethernet and InfiniBand EDR. Buyers should confirm which standards and protocols apply to the exact cable model and target equipment.

Before placing an order, review the following points:

• Source port support: Verify that the QSFP28 port can be configured for four-way breakout.

• Destination interface capability: Confirm that each SFP28 port supports the intended 25G operating rate.

• Firmware and configuration: Check for platform-specific restrictions, supported port modes, and any required configuration changes.

• Equipment compatibility: Confirm that the cable is supported by the switch, server, network adapter, or other connected hardware.

• Protocol requirements: Match the intended network protocol and operating mode to the device and cable specifications.

• Environmental conditions: Check the cable's specified operating temperature and installation requirements.

• Part number and datasheet: Ensure that the ordered configuration, connector arrangement, and length correspond to the documented product.

These checks are particularly important in mixed-vendor networks. Equipment may use the same connector format but have different compatibility policies or restrictions relating to cable identification and supported operating modes. Confirming these details in advance can reduce commissioning delays and avoid unnecessary troubleshooting.

Installation and Link Testing

A structured installation process helps ensure that all four branches are connected and configured correctly.

First, confirm the port mapping and configure the source port for the required breakout mode according to the switch manufacturer's instructions. Depending on the platform, applying the configuration may require a port reset or other operational steps.

Next, connect the QSFP28 end to the designated source port and attach each SFP28 branch to its assigned destination. Handle the connectors carefully, avoiding excessive pulling or force. Route the cable so that it does not obstruct ventilation, rack doors, sliding equipment trays, or access to adjacent ports.

Once the assembly is installed, test each branch separately. Review interface status, negotiated speed, relevant switch logs, and error counters. A functioning QSFP28 source port does not necessarily indicate that all four SFP28 connections are working properly.

If one branch fails to establish a link, check the following:

1. Confirm that the correct destination port has been used.

2. Verify that the source port and breakout configuration are enabled as required.

3. Check that both connectors are fully seated.

4. Confirm that the connected devices support the cable and operating mode.

5. Review interface settings, administrative status, and relevant error messages.

6. Inspect the cable and connectors if configuration checks do not resolve the issue.

Replacing a cable should not be the first response to every link failure. Configuration mismatches, unsupported port modes, and incorrect port assignments can produce similar symptoms. Following a consistent verification procedure helps identify the actual cause more efficiently.

Choosing a DAC Supplier for Data Center Projects

For network deployments, supplier selection should take into account more than price or nominal data rate. Buyers also need accurate product documentation, suitable cable configurations, appropriate lengths, and support for the intended application.

Infinol Technology (Shenzhen) Co., Ltd. focuses on the research, development, production, and sales of optical communication products. Its portfolio includes optical transceivers, direct attach copper cables, active optical cables, and MPO/MTP trunk cables for data centers, telecommunications, storage, and other data communication applications. The company also provides OEM and ODM services for active and passive optical communication products.

When requesting a quotation for the DAC 100Gb/s cable, buyers should specify whether they require a standard QSFP28-to-QSFP28 assembly or a QSFP28-to-four-SFP28 breakout version. Providing the equipment models, port speeds, required length, protocol, and intended connection layout helps clarify the technical requirements.

For larger deployments, it is also useful to confirm the exact part number, applicable specifications, equipment compatibility, and any testing or documentation requirements before ordering. These details can help procurement teams coordinate with network engineers and reduce the risk of selecting an unsuitable cable configuration.

Making 100G Breakout Connections Easier to Manage

A 100G QSFP28-to-four-SFP28 DAC can provide four 25G physical connections from a compatible 100G interface, making it useful for selected server, storage, and data center networking layouts. Its effectiveness depends on correct port configuration, compatible equipment, suitable cable length, and a clear plan for mapping the four branches.

The DAC 100Gb/s cable range from Infinol includes both standard QSFP28 copper assemblies and four-way breakout configurations for short-distance connectivity. By checking the equipment requirements before installation and verifying every link after deployment, network teams can build a more organized and maintainable cabling layout.

For projects that require a specific port arrangement or cable length, Infinol Technology (Shenzhen) Co., Ltd. can be consulted about the available configurations and relevant technical specifications. Careful selection and deployment of the DAC 100Gb/s cable can help ensure that the chosen interconnect matches the requirements of the network infrastructure.

http://www.infinol.com
Infinol Technology (shenzhen) Co., Ltd​

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