HPE 844477-B21 25GbE SFP28 to SFP28 3M Direct Attach Copper Cable

The HPE 844477-B21 is a 25 Gigabit SFP28 to SFP28 Direct Attach Copper (DAC) cable at 3 meters — the right interconnect for high-density top-of-rack server and switch deployments where you need 25GbE throughput without the cost and complexity of optical transceivers. If you're wiring HPE servers or switches across adjacent racks or within the same row, this cable eliminates both the transceiver cost and the fiber infrastructure entirely, delivering wire-speed 25GbE at a fraction of the price of an active optical solution. For HPE networking and storage connectivity, the HPE networking accessories catalog covers the full range of compatible interconnect options.

Overview

Direct Attach Copper cables occupy a specific and well-understood niche in data center cabling: short-reach, high-bandwidth, low-latency connections where the distance fits (3 meters covers most same-rack and adjacent-rack scenarios) and power budget is a priority. The 844477-B21 operates at 25 GBd with a bit error rate ceiling of 10⁻¹² — that's the standard acceptable threshold for sustained 25GbE operation, meaning link errors won't accumulate into performance degradation under normal thermal and signal conditions. It draws a 3.3 V supply at 4 mA, which keeps it well within the power envelope of any SFP28 port without stressing the switch or HBA's per-port budget.

For buyers comparing this to fiber-based network cables and transceivers, the practical tradeoff is straightforward: DAC wins on cost and simplicity for runs under 5 meters; active optical takes over beyond that. At 3 meters, this cable is the correct choice for nearly all same-row rack connections.

Key Features

• 25 GBd Data Rate: Delivers full 25GbE throughput between SFP28 ports — relevant when connecting 25G-capable HPE ProLiant servers to 25G top-of-rack switches where 10GbE would create a bottleneck at the NIC.
• 3-Meter Length: Covers the vast majority of same-rack and one-rack-unit-gap deployments. Measure your rack spacing before ordering — DAC cables aren't field-cuttable, and 3M is a common sweet spot for adjacent-rack top-of-rack wiring in standard 600mm aisle configurations.
• 10⁻¹² Bit Error Rate Ceiling: The IEEE 802.3by-mandated BER floor. In practice this means you won't see link-layer retransmits accumulating into TCP throughput degradation or storage I/O latency spikes under sustained load — a real concern with substandard or grey-market DAC cables that cut corners on the twinax conductor quality.
• 3.3 V / 4 mA Supply Draw: Extremely low power consumption. At 4 mA, this cable draws negligible power per port compared to active optical transceivers — meaningful when you're populating a 32-port 25G switch and need to stay within the total switch power budget.
• 100 Ohm Cable Impedance: Matched to the differential signaling standard for SFP28, which directly affects signal integrity. Impedance mismatch is a common cause of BER degradation at 25G — the 100 Ohm spec here is correct for the application.
• 4.3 ns/m Cable Time Delay: Low propagation delay across the 3-meter run. For latency-sensitive workloads — high-frequency financial applications, low-latency storage (NVMe-oF), or clustered compute — DAC cables at this delay spec add under 13 ns total, which is effectively zero compared to switch-level processing latency.
• 10 dB/10m Cable Insertion Loss: At 3 meters, actual insertion loss is approximately 3 dB — well within the SFP28 receiver sensitivity budget. This is why DAC is reliable at short distances and unreliable at longer ones; insertion loss scales with length, and 3 dB at 3M is a safe operating margin.
• MSA SFF-8402 Compliant: SFF-8402 is the Multi-Source Agreement governing 25G SFP28 DAC electrical interface. Compliance means the connectors and signaling conform to the standard that all SFP28 switches and adapters are designed to accept — reducing compatibility risk when pairing with non-HPE equipment that also meets SFF-8402.
• IEEE 802.3by Compliant: The formal 25 Gigabit Ethernet standard. This is the compliance marker procurement teams need for network infrastructure audits and standards-based purchase approvals.
• RoHS Compliant: Meets EU Restriction of Hazardous Substances requirements. Required for any deployment in regulated environments, EU-export equipment, or sites with environmental compliance mandates.
• Operating Temperature 0 to 70°C: Standard commercial temperature range. Data center environments with proper cooling fall well within this range. If you're deploying in an industrial environment with elevated ambient temperatures, verify rack inlet temperatures stay below 70°C under load.
• Storage Temperature -40 to 85°C: Wide storage range means pre-staged spares can be stored in unheated warehouses or equipment closets without degradation risk.

Integration and Compatibility

The 844477-B21 is designed for HPE SFP28 ecosystems — including HPE FlexFabric, HPE Aruba CX, and HPE ProLiant server HBAs and CNAs with 25GbE SFP28 ports. MSA SFF-8402 compliance provides a baseline for interoperability with third-party SFP28 ports, though HPE switches may flag non-HPE DACs depending on firmware settings. Verify compatibility in mixed-vendor environments before mass deployment. This cable does not support 100GbE QSFP28 ports — it is strictly SFP28 to SFP28. For a full view of compatible HPE switching and server options, the network switches category covers compatible top-of-rack platforms.

For PoE switch planning and data center structured cabling design guidance, the network cabling and infrastructure guide covers topology decisions, cable tray planning, and DAC versus fiber selection criteria for common deployment sizes.

Complement this DAC cable with compatible SFP28 transceivers and fiber optic modules for longer-reach runs beyond the 3-meter DAC ceiling, or where plenum-rated pathways require optical solutions.

Frequently Asked Questions

Q: What is the maximum supported data rate for the HPE 844477-B21?

A: The 844477-B21 operates at 25 GBd, supporting 25 Gigabit Ethernet per IEEE 802.3by. It is an SFP28 to SFP28 interface and does not support 100GbE or QSFP28 ports.

Q: Is the 844477-B21 compatible with non-HPE switches that have SFP28 ports?

A: The cable is MSA SFF-8402 compliant, which is the standard governing SFP28 DAC interfaces. Most SFF-8402-compliant SFP28 ports should accept it, but HPE switches may issue compatibility warnings with non-HPE DACs depending on firmware. Verify in your specific switch firmware version before deploying at scale in mixed-vendor environments.

Q: What is the bit error rate specification for the 844477-B21?

A: The specified bit error rate ceiling is 10⁻¹², which is the standard IEEE 802.3by threshold for 25GbE operation. This means fewer than one bit error per trillion bits transmitted under normal operating conditions.

Q: What operating temperature range does the 844477-B21 support?

A: The operating temperature range is 0°C to 70°C. This covers standard data center environments. Storage temperature range is wider: -40°C to 85°C.

Q: Does the 844477-B21 require external power?

A: No. The cable draws power directly from the SFP28 host port at 3.3 V / 4 mA — well within the standard SFP28 power budget. No external power supply is required.

Q: Is the 844477-B21 RoHS compliant?

A: Yes. The 844477-B21 is RoHS compliant, meeting EU Restriction of Hazardous Substances requirements.

Ted Perry

The 844477-B21 (often searched as 844477 B21) is what I reach for when the conversation is short-reach 25GbE interconnects in HPE-heavy environments. The 4.3 ns/m propagation delay across a 3-meter run adds under 13 ns end-to-end — effectively invisible at the application layer, which matters when you're connecting NVMe-oF initiators to storage targets and every microsecond of fabric latency shows up in IOPS benchmarks.

Technical Highlights:

• 25 GBd at 10⁻¹² BER: The error rate ceiling is the IEEE 802.3by standard — not a marketing claim. In practice, a quality DAC at 3 meters running within its insertion loss budget (approximately 3 dB at this length against a 10 dB/10m spec) will sustain that BER under continuous load without link retrains.
• 3.3 V / 4 mA Power Draw: At 4 mA per port, you can populate a full 32-port 25G switch with DAC cables and the cumulative SFP28 port power draw is negligible compared to the switch ASIC and fan load. This matters when you're calculating total rack PDU load in high-density deployments.
• 100 Ohm Differential Impedance: Matched to SFP28 signaling spec. Impedance discontinuities are the leading cause of 25G DAC signal integrity failures — connectors that deviate from 100 Ohm differential see reflections that push BER past 10⁻¹². This cable holds the spec.

Deployment Considerations:

• Verify HPE switch firmware DAC allowlist before deploying in mixed-vendor environments. Some HPE Aruba CX and FlexFabric firmware versions restrict third-party SFP28 DACs by default — the 844477-B21 as an HPE-branded cable avoids this issue on HPE ports, but confirm if the far-end switch is non-HPE.
• The 0–70°C operating range is the watch point for dense blade chassis or high-airflow-restricted rack positions. Measure inlet air temperature at the SFP28 cage location under peak load, not just ambient room temperature — a poorly cooled rack row can push transceiver pocket temps above 70°C even with a 22°C data center set point.

For HPE ProLiant server HBA-to-25G-ToR switch wiring in same-row rack configurations — particularly NVMe-oF storage fabrics and hyperconverged compute clusters where cable counts run high and optical infrastructure budget is constrained — the 844477-B21 is the correct, low-risk interconnect choice.