What is 844477-B21? HPE 25GB SFP28 to SFP28 3m DAC Guide

As data center networks continue to adopt 25GbE connectivity, short-distance links between servers, network adapters, and switches require cabling that can deliver high bandwidth without unnecessary optical components. SFP28-based connections have become a practical choice for these environments, while Direct Attach Copper (DAC) cables provide a simple approach for rack-level interconnections. Choosing the right cable, however, requires more than checking the connector type and data rate.

This is where 844477-B21 comes into focus. HPE 844477-B21 is a 25Gb SFP28-to-SFP28 3m Direct Attach Copper cable designed for short-distance network connections. Its SFP28 interfaces, copper transmission medium, and fixed 3m length make it particularly relevant to server-to-switch and other high-speed connections within data center racks. Understanding its specifications and compatibility is essential for determining whether it fits a specific 25GbE deployment.

This guide examines the key aspects of 844477-B21 to help readers evaluate its role before deployment, including:

• Product definition and core technical specifications
• SFP28 DAC operating principles and typical applications
• Device, port, and system compatibility considerations
• Installation requirements, advantages, and limitations
• Practical factors for evaluating 844477-B21 before deployment

Together, these points provide a clear technical foundation for understanding where 844477-B21 fits in modern 25GbE networks and how to assess whether its design matches a particular connectivity requirement.

🚩 What Is 844477-B21?

844477-B21 is an HPE 25Gb SFP28-to-SFP28 3m Direct Attach Copper (DAC) cable designed for short-distance 25GbE connectivity. It combines two permanently attached SFP28 interfaces with a copper cable assembly, allowing compatible network devices to establish a high-speed electrical connection without separate optical transceivers or fiber patch cords.

844477-B21 Product Definition

HPE 844477-B21 is a 3m 25Gb SFP28 DAC cable intended for direct connections between compatible SFP28 ports. Unlike a conventional optical link, the cable integrates the interface assemblies and copper transmission medium into a single connection.

Its main characteristics include:

• Product number: 844477-B21
• Data rate: 25GbE-class connectivity
• Interface: SFP28 to SFP28
• Transmission medium: Direct Attach Copper
• Cable length: 3m
• Cable construction: Integrated SFP28 ends with a fixed copper cable
• Typical role: Short-distance server, switch, and rack-level interconnections

The integrated design reduces the number of components required for a short 25GbE link. Instead of installing two optical SFP28 modules, two fiber connectors, and a fiber patch cable, a compatible DAC connection can be established using the single 844477-B21 cable assembly.

This distinction is important when evaluating the product because 844477-B21 should not be treated as an independent SFP28 optical transceiver. Its performance and deployment characteristics are determined by the complete DAC assembly and the compatibility of the devices connected at both ends.

What Does SFP28 to SFP28 Mean?

SFP28-to-SFP28 means that both ends of 844477-B21 use the SFP28 form factor, allowing the cable to connect two compatible SFP28 ports directly. SFP28 is commonly associated with 25GbE network interfaces and is designed for higher-speed connectivity than traditional SFP-based 1GbE interfaces.

In a typical connection, the two ends are installed into:

1. A 25GbE SFP28 port on a server network adapter.
2. A compatible 25GbE SFP28 port on a network switch or another supported device.

The connection remains a point-to-point electrical link between the two ports. Because both ends use SFP28 interfaces, there is no need for an intermediate connector or media conversion component.

It is also important to distinguish an SFP28-to-SFP28 DAC from a breakout cable. A standard 844477-B21 connection uses one SFP28 interface at each end and provides a direct link between two compatible ports rather than dividing one higher-density interface into multiple lower-rate connections.

🚩 844477-B21 Technical Specifications

The 844477-B21 technical specifications define it as a short-distance 25GbE interconnect based on the SFP28 form factor and Direct Attach Copper technology. Its 3m length, electrical characteristics, physical dimensions, and compliance specifications determine how it can be integrated into a rack-level network.

844477-B21 Core Specifications at a Glance

The most important 844477-B21 specifications are its 25GbE data rate, SFP28-to-SFP28 interface, 3m cable length, and copper transmission medium. These characteristics make the cable primarily suitable for short, direct connections between compatible 25GbE devices.

These specifications should be considered together rather than individually. For example, the 3m length determines the physical deployment scope, while the SFP28 interface and 25GbE data rate determine whether the cable matches the intended network ports.

3m Cable Length and Physical Characteristics

The 3m cable length is one of the defining characteristics of 844477-B21 and makes it particularly relevant to short-distance connections within data center racks. A 3m cable is approximately 9.84ft long, providing additional routing flexibility compared with shorter DAC assemblies while avoiding the excess slack that can occur with unnecessarily long cables.

The published physical characteristics also affect installation and cable management:

• Cable length: 3m, approximately 9.84ft.
• Cable diameter: 4.5±0.2mm.
• Minimum single-bend radius: 23mm.
• Minimum repeated-bend radius: 45mm.
• Transmission medium: Copper.
• Connector configuration: SFP28 at both ends.

The bend-radius requirements are particularly important in high-density racks. The cable should not be sharply folded or forced into a space smaller than its specified minimum radius. Maintaining appropriate routing space helps reduce mechanical stress and makes future servicing easier.

The fixed 3m length should also be evaluated against the actual distance between devices. It is well suited to many server-to-switch and nearby switch-to-switch connections, but the physical rack layout should be checked before installation to prevent excessive tension or unnecessary cable loops.

Electrical Characteristics

The electrical specifications of 844477-B21 describe how the copper assembly handles high-speed signals between the two SFP28 interfaces. The key published values include a characteristic impedance of 90–110Ω and a time delay of 4.5ns/m.

These electrical parameters can be understood as follows:

• Characteristic impedance: 90–110Ω, defining the cable's nominal electrical impedance range.
• Time delay: 4.5ns/m, indicating the signal propagation delay through the cable.
• Signal transmission: Electrical rather than optical.
• Connection architecture: Direct point-to-point connection between the two SFP28 interfaces.

At 25GbE speeds, maintaining appropriate electrical characteristics is important for signal integrity. The cable, connectors, and host interfaces must work together as a complete high-speed channel rather than being evaluated only by their nominal data-rate labels.

Standards and Compliance

844477-B21 also incorporates specifications relevant to SFP28 mechanical and electrical implementation and environmental compliance. In particular, the cable is associated with SFF-8665 and RoHS requirements.

The main compliance points are:

• SFF-8665: Relevant to SFP28-related high-speed connector and interface specifications.
• RoHS: Addresses restrictions on certain hazardous substances in electronic and electrical equipment.
• Form-factor compatibility: The SFP28 ends follow the physical interface requirements associated with the SFP28 ecosystem.

These standards provide an important technical baseline, but compliance should not be confused with universal device interoperability. A cable can conform to relevant industry specifications while a particular switch, server adapter, or network platform may still impose its own supported-cable or firmware requirements.

🚩 How Does 844477-B21 Work?

The 844477-B21 works by carrying high-speed electrical signals directly between two compatible SFP28 ports through an integrated copper cable assembly. Unlike an optical SFP28 connection, it does not require electrical-to-optical conversion or a separate fiber link, making its architecture particularly suitable for short-distance 25GbE connections.

Signal Transmission Through Direct-Attach Copper

The 844477-B21 transmits network data as electrical signals over copper conductors between its two permanently attached SFP28 ends. Each end plugs directly into a compatible SFP28 port, creating a point-to-point connection between the two network devices.

The basic signal path can be understood as follows:

1. A network device sends 25GbE electrical signals through its SFP28 port.
2. The signal enters the integrated SFP28 interface of the 844477-B21.
3. The copper cable carries the electrical signal across the 3m link.
4. The SFP28 interface at the opposite end delivers the signal to the receiving device.
5. The receiving port processes the incoming data through its network interface.

Because the transmission medium is copper, the connection does not need separate optical transmitters, optical receivers, or fiber patch cords. This integrated architecture reduces the number of individual components in a short-distance link.

The complete cable assembly therefore functions as a direct electrical interconnect. Its performance depends not only on the cable itself but also on the electrical characteristics and compatibility of the SFP28 ports connected at both ends.

25GbE Connectivity Between Network Devices

The 844477-B21 is designed to establish short-distance 25GbE connectivity between devices equipped with compatible SFP28 interfaces. A common configuration connects a server or network adapter to a switch, although the same basic architecture can support other compatible point-to-point connections.

Typical connection scenarios include:

• Server-to-switch: A 25GbE server NIC connects directly to an SFP28 switch port.
• Switch-to-switch: Two compatible SFP28 switch ports are connected for a short-distance interconnect.
• Rack-level networking: Servers and switches located within the same rack or nearby rack positions are connected using the 3m DAC.
• High-speed host connectivity: A compatible network adapter uses an SFP28 port to establish a 25GbE link with another supported device.

For a successful connection, both endpoints must support the appropriate SFP28 operating mode and DAC configuration. The physical presence of an SFP28 slot alone is not sufficient because some ports may have restrictions on supported modules, cables, speeds, or firmware configurations.

When the endpoints are compatible, the 844477-B21 provides a straightforward physical path for high-speed Ethernet traffic without introducing a separate optical conversion stage. Port configuration should still be verified according to the specific switch or network adapter documentation.

🚩 844477-B21 Applications in 25GbE Networks

The 844477-B21 is primarily suited to short-distance 25GbE connections where two compatible devices use SFP28 ports and can be physically linked with a 3m copper assembly. Its Direct Attach Copper design makes it especially relevant to server-to-switch connections, short switch interconnects, and high-density data center racks.

Server-to-Switch Connections

The 844477-B21 is well suited to connecting a 25GbE server network adapter directly to a compatible SFP28 switch port. This configuration provides a simple point-to-point connection between the server and access-layer switching infrastructure without requiring separate optical modules and fiber patch cables.

Common server-to-switch scenarios include:

• Connecting a 25GbE server NIC to an SFP28 switch port.
• Linking compute servers to top-of-rack (ToR) switches.
• Connecting storage servers that use compatible 25GbE network interfaces.
• Establishing short connections between equipment positioned within the same rack.

The 3m cable length provides useful routing flexibility for many rack layouts. However, the actual distance between the server and switch should be considered before installation so that the cable can be routed without excessive tension, sharp bends, or unnecessary slack.

Switch-to-Switch Interconnects

The 844477-B21 can also serve as a short-distance interconnect between compatible switches equipped with SFP28 ports. This is useful when the two switching devices are positioned close enough for a 3m copper connection.

Potential applications include:

• Short 25GbE links between adjacent switches.
• Rack-level switch interconnections.
• Connections between access and aggregation equipment located nearby.
• Temporary or permanent high-speed links within a controlled rack environment.

Because the cable has a fixed 3m length, the physical placement of the switches should be evaluated before deployment. A suitable routing path should allow the cable to reach both ports while maintaining the specified bend-radius requirements.

Data Center and High-Density Rack Deployments

The 844477-B21 is particularly relevant to high-density rack environments where multiple 25GbE devices need short, organized interconnections. Its integrated SFP28-to-SFP28 copper design eliminates the need to manage separate optical transceivers and fiber patch cords for each short link.

Its rack-level advantages can include:

• Simplified component count: One integrated cable assembly provides both SFP28 interfaces and the copper connection.
• Straightforward installation: The cable can be connected directly to compatible SFP28 ports.
• Efficient short-range connectivity: The 3m length can accommodate many server-to-switch layouts.
• Simpler cable management: Fewer separate components can reduce connector and patch-cable complexity.
• High-speed connectivity: The SFP28 interface supports 25GbE-class network connections.

In dense deployments, however, simplicity should not come at the expense of cable organization. Multiple DAC cables can occupy significant rack space, so routing should preserve airflow, service access, and the specified bend radius.

🚩 844477-B21 Compatibility Considerations

844477-B21 compatibility depends on more than having an SFP28 slot. A successful 25GbE connection requires the connected devices to support the SFP28 interface, the intended DAC configuration, the required link speed, and any platform-specific firmware or cable restrictions. Checking these factors before installation helps reduce link-detection and interoperability problems.

SFP28 Port Compatibility

Both endpoints must provide compatible SFP28 ports capable of supporting the intended 25GbE DAC connection. The physical SFP28 form factor establishes the basic mechanical interface, but it does not by itself confirm that the port supports every type of SFP28 cable or operating mode.

Before connecting 844477-B21, check the following:

• Confirm that both devices have SFP28 ports.
• Verify that the ports support 25GbE operation.
• Check whether the ports support DAC cables rather than only optical SFP28 modules.
• Confirm the supported cable or transceiver types in the device documentation.
• Check whether the ports require a specific configuration for 25GbE operation.

This distinction is important because an SFP28 port can have the correct physical connector while still imposing restrictions on supported cables. Compatibility should therefore be evaluated at both the physical-interface and system-operation levels.

HPE Server and Network Device Compatibility

When deploying 844477-B21 with HPE equipment, the server, network adapter, switch, or interconnect should be checked against the relevant HPE compatibility documentation. The supported hardware configuration provides the most reliable indication of whether the cable is appropriate for a particular system.

Important checks include:

1. Identify the exact HPE server or network device model.
2. Identify the SFP28 adapter or network interface installed in the system.
3. Confirm that the relevant port supports 25GbE DAC connectivity.
4. Review the applicable HPE compatibility or supported-cable documentation.
5. Verify firmware and software requirements where applicable.

This approach is more reliable than assuming that all HPE SFP28 ports support the same cable configurations. Different platforms, adapters, and firmware versions can have different interoperability requirements.

Third-Party Device Compatibility

844477-B21 should not automatically be assumed to work with every third-party SFP28 device. Although the SFP28 form factor is standardized, vendors can implement platform-specific restrictions related to cable identification, supported configurations, firmware, or port policies.

When connecting 844477-B21 to third-party equipment, evaluate:

• The switch or network adapter's supported SFP28 DAC list.
• The manufacturer's compatibility documentation.
• Supported 25GbE operating modes.
• DAC recognition and vendor-coding requirements, if applicable.
• Firmware or software restrictions.
• Any vendor-specific policies concerning third-party connectivity components.

The key point is that standardized interfaces improve interoperability but do not guarantee universal compatibility. A third-party switch may recognize an SFP28 physical connection yet reject or fail to activate a particular DAC assembly because of platform-level restrictions.

Port Speed and Configuration Checks

The two connected ports should be configured and capable of operating at the required 25GbE speed. A compatible physical connection can still fail to establish a working link if the port configuration or supported operating mode does not match the network design.

Before deployment, verify:

• Both endpoints support 25GbE operation.
• The intended interfaces are enabled.
• Port speed settings are compatible.
• Auto-negotiation behavior matches the device requirements.
• The selected port mode supports the DAC connection.
• No unsupported breakout or adapter configuration is being introduced.

These checks are especially useful when troubleshooting a link that remains down after the cable has been physically installed. If the cable is detected but the interface does not establish a stable 25GbE connection, inspect port configuration and platform support before assuming that the cable itself is defective.

🚩 How to Choose the Right 844477-B21 Deployment Scenario

The right 844477-B21 deployment scenario is one where the connected devices have compatible SFP28 ports, the required link is a short-distance 25GbE connection, and the fixed 3m cable length fits the physical layout. Evaluating distance, port compatibility, rack topology, and cabling requirements first helps determine whether a 3m DAC is appropriate.

When a 3m DAC Is the Right Choice

844477-B21 is a suitable choice when two compatible 25GbE SFP28 devices are located close enough to be connected by a 3m copper cable. Its integrated SFP28-to-SFP28 design is particularly practical for predictable rack-level connections.

Consider using a 3m DAC when:

• The endpoints are located within a short physical distance.
• Both devices support compatible SFP28 DAC connections.
• A 25GbE point-to-point link is required.
• The rack layout provides a practical route for a 3m cable.
• A simple integrated copper connection is preferable to separate optical components.
• The deployment does not require the longer reach or cabling flexibility of fiber.

A 3m cable can also provide more routing flexibility than very short DAC assemblies. However, the extra length should still be managed carefully to avoid unnecessary loops or interference with other rack equipment.

When to Consider a Different Cable Length

A different DAC length should be considered when the physical distance between endpoints does not match the practical routing requirements of a 3m assembly. Cable selection should account for the actual path through the rack rather than measuring only the straight-line distance between two ports.

Consider another cable length when:

1. The endpoints are positioned very close together and 3m would create excessive slack.
2. The equipment is arranged so that a 3m cable cannot provide an efficient routing path.
3. The cable must pass through a longer or more complex rack-management route.
4. The deployment would require excessive bending or tension to accommodate the fixed length.

Using an unnecessarily long cable can make high-density rack management more difficult, while an insufficient cable length can place mechanical stress on the connectors or cable assembly.

For this reason, the physical layout should be mapped before installation. The goal is to select a cable length that reaches both endpoints while maintaining proper routing, bend radius, airflow, and service access.

🚩 844477-B21 Installation and Deployment Best Practices

Proper installation of 844477-B21 starts with confirming endpoint compatibility and continues with careful cable routing and post-installation link verification. Because it is a fixed 3m SFP28-to-SFP28 DAC assembly, both the electrical compatibility and physical installation conditions should be checked before the cable is connected.

Pre-Installation Checks

Before installing 844477-B21, verify that the two intended endpoints support the required SFP28 DAC connection and that the 3m cable length is suitable for the physical layout. These checks help identify compatibility or installation issues before they affect network operation.

Use the following pre-installation checklist:

1. Confirm the exact cable part number is 844477-B21.
2. Verify that both endpoints provide compatible SFP28 ports.
3. Confirm that the intended ports support 25GbE operation.
4. Check the device manufacturer's supported DAC or cable list.
5. Review relevant firmware and software requirements.
6. Measure or estimate the actual cable-routing path between the two ports.
7. Inspect the SFP28 ends and copper cable for visible damage or deformation.

These checks are particularly important when one or both endpoints are from a different vendor. Physical SFP28 compatibility does not necessarily mean that the complete system will recognize and operate with a particular DAC assembly.

Once compatibility and physical requirements have been confirmed, the cable can be installed without introducing unnecessary mechanical stress.

Cable Routing and Bend Radius

844477-B21 should be routed without exceeding its specified mechanical limits. The cable has a 4.5±0.2mm diameter, with a minimum single-bend radius of 23mm and a minimum repeated-bend radius of 45mm, so tight turns should be avoided during installation.

Follow these routing practices:

• Keep the cable path as direct as practical.
• Avoid sharp bends near either SFP28 connector.
• Do not compress the cable beneath equipment or other cables.
• Avoid pulling the cable excessively during installation.
• Maintain the specified bend radius throughout the routing path.
• Keep cable loops controlled rather than tightly coiled.
• Route cables so they do not obstruct equipment airflow or service access.

In high-density racks, cable organization is particularly important because multiple DAC assemblies can quickly increase cable density around switch ports. A clean routing path reduces mechanical stress and makes later troubleshooting or equipment replacement easier.

The 3m length should also be used efficiently. Excess cable should not be forced into tight spaces simply to keep it out of sight, because excessive bending can create unnecessary mechanical stress.

Link Verification After Installation

After 844477-B21 has been installed, verify the physical link and operating status from both connected devices. A successful physical insertion does not necessarily mean that the network has established a functioning 25GbE connection.

The verification process should include:

1. Check whether both endpoints detect the connected SFP28 DAC.
2. Confirm that the interface becomes operational.
3. Verify the configured or negotiated link speed.
4. Check interface status and error counters.
5. Confirm that traffic can pass between the two endpoints.
6. Monitor the connection for link drops or recurring errors.

If the link remains down, begin with the simplest possible checks: confirm that both connectors are fully seated, verify port configuration, and review whether the devices officially support the intended DAC connection.

If the cable is detected but the link does not operate at the expected speed, inspect the endpoint configuration and supported operating modes. Vendor documentation should also be reviewed for firmware, cable-recognition, or interoperability requirements.

Following these installation and verification practices allows 844477-B21 to be evaluated as a complete connectivity solution rather than simply as a physical cable. This is especially important in 25GbE environments where port compatibility, signal integrity, and physical cable management all contribute to reliable link operation.

🚩 FAQs About 844477-B21

What is 844477-B21?

844477-B21 is an HPE 25Gb SFP28-to-SFP28 3m Direct Attach Copper (DAC) cable for short-distance network connectivity.

Is 844477-B21 an optical transceiver?

No. 844477-B21 is an integrated copper DAC cable assembly rather than a standalone optical transceiver.

What speed does 844477-B21 support?

844477-B21 is designed for 25GbE network connections using SFP28 interfaces.

What type of connector does 844477-B21 use?

It uses an SFP28 interface at both ends, forming a direct SFP28-to-SFP28 connection.

Can 844477-B21 connect two SFP28 ports?

Yes. It can connect two compatible SFP28 ports when the devices support the required 25GbE DAC configuration.

Is 844477-B21 compatible with every SFP28 switch?

No. Compatibility depends on the switch's supported DAC types, port capabilities, firmware, and vendor-specific requirements.

🚩 Conclusion

844477-B21 is an HPE 25Gb SFP28-to-SFP28 3m Direct Attach Copper (DAC) cable designed for short-distance 25GbE connectivity. Its integrated SFP28 interfaces, copper transmission medium, and fixed 3m length make it a practical solution for compatible server-to-switch and rack-level network connections.

The key points to remember are:

• 844477-B21 provides 25GbE-class connectivity through SFP28 interfaces.
• It uses a 3m Direct Attach Copper cable rather than optical fiber.
• Its electrical and physical specifications should be considered during deployment.
• Compatibility depends on the SFP28 ports, supported DAC configurations, firmware, and device platform.
• Proper routing and bend-radius management are important for reliable installation.
• Optical SFP28 solutions may be more suitable when longer reach or greater cabling flexibility is required.

Understanding these factors makes it easier to determine whether 844477-B21 matches a specific 25GbE network topology. For organizations evaluating compatible optical modules and other high-speed network connectivity solutions, the LINK-PP Official Store provides additional options to consider alongside the requirements of the target network.