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QSFP and QSFP28 are both transceivers used in data centers and networks, but they differ mainly in speed and intended application. QSFP (and its enhanced version QSFP+) supports 40G data rates, while QSFP28 is designed for 100G data rates.
Here is a quick overview of their key differences:
| Feature | QSFP/QSFP+ | QSFP28 |
| Primary Application | 40 Gigabit Ethernet (40GbE) | 100 Gigabit Ethernet (100GbE) |
| Data Rate | 40 Gbps aggregate (4 x 10 Gbps lanes) | 100 Gbps aggregate (4 x 25 Gbps lanes) |
| Form Factor | Same physical size; hot-pluggable | Same physical size; hot-pluggable |
| Typical Connectors | LC Duplex or MPO/MTP | LC Duplex or MPO/MTP |
| Typical Standards | IEEE 802.3ba, 40GBASE-SR4, LR4 | IEEE 802.3bm, 100GBASE-SR4, LR4, CWDM4 |
| Power Consumption | Generally lower | Generally higher |
| Key Use Case | Data center aggregation, high-performance computing | Data center core, high-density 100G connections |
Technical and Application Differences
Beyond the specifications, their real-world use differs in several key ways:
Speed and Lane Configuration: Both are "Quad" modules, meaning they use four lanes. However, QSFP+ uses four 10 Gbps lanes to achieve 40 Gbps, whereas QSFP28 uses four 25 Gbps lanes to achieve 100 Gbps.
Flexibility and Breakout Modes: QSFP28 is more flexible. Beyond the standard 4x25G mode, some variants can operate in 2x50G or 1x100G modes. Both can also be "broken out" to connect to lower-speed devices. For example, a QSFP+ port can be split to connect four 10G devices, and a QSFP28 port can be split to connect four 25G devices.
Physical Compatibility: Their same physical size allows for important backward compatibility: a QSFP28 port on a modern switch can typically accept a QSFP+ module, but it will run at the lower 40G speed. The reverse (plugging QSFP28 into a QSFP+ port) is not supported
How to Choose Between Them
Your choice depends almost entirely on your network's speed requirements and existing infrastructure:
Choose QSFP/QSFP+ if you are building or maintaining a 40G network backbone, connecting switches that require 40G uplinks, or looking for a cost-effective solution where 40G performance is sufficient.
Choose QSFP28 if you are deploying a new 100G data center core or spine, require future-proof high-density connectivity, or need the flexibility for breakout configurations to multiple 25G servers.
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