25G Ethernet vs. 40G Ethernet: Which to Choose?

Nowadays, the growth in demand for higher bandwidth can be achieved by a shift to a higher transmission speed such as 100G. To upgrade to 100G, there’re two approaches: 10G to 40G to 100G, and 10G to 25G to 100G. It seems that the key lies in the deployment of 25G and 40G, so what are the differences between them? This article explains the difference between 25G Ethernet and 40G Ethernet, and how to choose the one that suits your needs the best.

25G Ethernet Overview

25G Ethernet standard was put forward by the 25 Gigabit Ethernet Consortium, which consists of leading companies including Arista, Broadcom, Google, Mellanox Technologies, and Microsoft in 2014. The goal is to promote the standardization and use of 25G Ethernet.

Since businesses need to upgrade constantly, 10G networks will be ultimately replaced in the future. 25G products like 25G switches, 25G DAC and AOC cables have received more and more recognition. Many providers have introduced 25GbE switches to achieve optimized network performance.

” Also check – FS 25G Campus Switches and FS 25G Data Center Switches

These 25G network switches are often used as ToR or leaf switches to connect the servers and terminal equipment. 25G Ethernet is an incremental update from 10G Ethernet. So for 25G and 10G Ethernet switches with the same port density, 25G switches and optics provide 2.5 times more performance and bandwidth than 10G switches, which helps reduce power and cost.

40G Ethernet Overview

The official introduction of 40G Gigabit Ethernet was in 2008, and it was approved in 2010. 40G Gigabit Ethernet (40GbE) is a standard developed by the IEEE 802.3ba Task Force. It enables the transfer of Ethernet frames at 40GbE per second. 40GbE runs on Quad Small Form Factor Pluggable (QSFP+) cabling, which can support high-bandwidth applications like video on demand and high-performance computing.

Compared with 25G Ethernet, 40G standard is more mature. There’re many types of products for 40G applications, including MTP/MPO trunk cable assemblies, 40G QSFP+ optical transceivers and 40Gb switch, which are widely used for networking.

” Also check – A Closer Look Into 40G Ethernet

In data centers, 40G switches are used as the aggregation/leaf switches, while they can act as core/spine switches for small and medium enterprises. When upgrading 10G to 40G Ethernet, users can use 40G QSFP+ to 4x10G SFP+ DAC/AOC cables to achieve this upgrade, or choose MTP/MPO to LC breakout cables and 40G transceivers solution according to their actual budget and transmission distance. For connecting two 40GbE switches, they need to choose MTP/MPO trunk cables or 40G QSFP+ to QSFP+ DAC/AOC cables.

25G vs. 40G Ethernet: Which to Choose?

There’re some factors that you should consider before making the final decision.


Generally, IT staff uses 25G Ethernet for switch-to-server applications, while using 40G for switch-to-switch applications. Thus, users should know their specific practices before designing their network.If 25G switch-to-switch connections can be largely promoted, 25G Ethernet may have a broader market.

Moreover, 25G optics are in great demand for the deployment of 5G networks, especially in 5G front-haul transmission, making it a new peak in development. As for 40G, it is still an optimal choice for high bandwidth connections with better efficiency than 10G and lower costs than 100G.

Network Switch Selection

25G and 40G network switches are designed to meet customers’ different uses. But note that, 25G can be more easily upgraded to 50G (2x25G) and 100G (4x25G). Due to the high performance of 25G chips with single-lane 25G serializer-deserializer technology, the port density and total broadband of the 25G switch is higher than the 40G switch when both 25G and 40G switches use the chip with 128 channels (see the following table). And it also can save capital expenditure and operating expenses.

Speed of portChannel rate (Gb/s)Number of channels per portAvailable portTotal broadband (Gb/s)


25G Ethernet adopts SFP28 transceivers, allowing both copper and fiber links. For interconnections in data center switches, SFP28 AOC/DAC cables are more suitable and cost-effective solutions, but the transmission distance is limited. When upgrading 10G to 25G, the existing LC cabling can be reused due to the high compatibility of 25G, avoiding costly and complex rewiring.

” Also check – 100G Network Migration: An Inevitable Roadmap for Future Data Centers

While 40G Ethernet commonly uses QSFP+ transceiver with MTP/MPO fiber optic cables for short transmission distances. But these cables have 12 optical fibers inside, which costs more than LC optical fibers of 10G. What’s worse, they are not compatible. If upgrading 10G to 40G, most of the fiber optic cables will be abandoned and rewired, which can be a huge expense.


Both 25G Ethernet and 40G Ethernet are the solutions to implement more robust and cost-effective networks. They can be applied in data centers with different uses and cabling solutions. So you should choose one according to your current demands and usage environment. FS offers our customers a variety of high-quality 25G and 40G networking products to help you build a reliable and high-performance network.