QSFP-40G-LR4 is a Cisco 40-Gigabit Ethernet QSFP+ transceiver designed for long-reach fiber links. It’s a 40GBase-LR4 optic that runs over single-mode fiber, using four CWDM wavelengths to deliver 40GbE over long distances in data center interconnect and campus backbone deployments.
Why buyers pick QSFP-40G-LR4 (plain English)
Long-distance 40G fiber Supports extended reach over single-mode fiber where SR4 optics won’t work.
Duplex SMF cabling Runs over standard LC duplex single-mode fiber — no parallel fiber required.
Data center & campus backbone ready Ideal for building-to-building links and long switch-to-switch connections.
Cisco-qualified optics Designed and tested for compatibility with Cisco 40G switching platforms.
Clean upgrade path Perfect when moving from 10G to 40G over existing single-mode fiber.
60-second spec box (QSFP-40G-LR4)
Form factor QSFP+
Speed 40GbE (40GBase-LR4)
Fiber type Single-mode fiber (SMF)
Wavelength CWDM (1271, 1291, 1311, 1331 nm)
Connector LC duplex
Max distance Up to ~10 km (fiber dependent)
Use case Long-reach data center, campus, and backbone 40G links.
Where it fits (and when to choose something else)
Perfect for:
Data center interconnects
Campus and building-to-building links
Long-distance 40G switch connections
Single-mode fiber environments
Choose something else if:
You’re using multimode fiber → SR4 optics
You only need short reach → QSFP-40G-SR4
You’re moving straight to 100G → QSFP28 optics
TL;DR
QSFP-40G-LR4 is Cisco’s 40GBase-LR4 QSFP+ optic: a long-reach, single-mode fiber transceiver delivering reliable 40GbE over distances up to 10 km.
Key specifications
Feature
Specification
Source
Form Factor
QSFP+
Data Rate
40 Gbps (4x10 Gbps)
Interface
40GBASE-LR4
Media Type
Single-Mode Fiber (SMF)
Connector
Duplex LC
Wavelength
1271 nm, 1291 nm, 1311 nm, 1331 nm (CWDM)
Maximum Distance
10 km (6.2 mi)
Operating Temperature
0°C to 70°C (32°F to 158°F)
Power Consumption
≤ 3.5 Watts
DDM Support
Yes (Digital Diagnostics Monitoring)
Standards Compliance
IEEE 802.3ba, QSFP+ MSA, OTU3 C4S1-2D1
Features and applications
High performance:The module delivers 40 Gbps throughput by using four coarse wavelength division multiplexing (CWDM) lanes, each running at 10 Gbps.
Long-distance reach:The QSFP-40G-LR4 is designed for long-distance data transmission over single-mode fiber, making it suitable for interconnecting data centers, enterprise campuses, and core networks.
Reliable monitoring:Digital Diagnostics Monitoring (DDM) allows network administrators to monitor the real-time operating parameters of the transceiver, such as temperature, voltage, and optical power.
Broad compatibility:While often associated with Cisco, it is designed to comply with Multi-Source Agreement (MSA) standards, ensuring interoperability with various networking equipment.
