Software for Open Networking in the Cloud (SONiC) is is a free and open source network operating system based on Linux.

SONiC is the open networking solution used in Microsoft’s Azure Cloud: is the networking switch software used in the lower layer of Azure Datacenter fabric (TOR and Aggregation).

Most important, is an open-source project available on SONiC GitHub Repository.

It was originally developed by Microsoft and the Open Compute Project. In 2022, Microsoft ceded oversight of the project to the Linux Foundation, who will continue to work with the Open Compute Project for continued ecosystem and developer growth.

SONiC is a uniquely extensible platform, with a large and growing ecosystem of hardware and software partners, that offers multiple switching platforms and various software components.

SONiC is built on the Switch Abstraction Interface (SAI), which defines a standardized API. Network hardware vendors can use it to develop innovative hardware platforms that can achieve great speeds while keeping the programming interface to ASIC (application-specific integrated circuit) consistent. Microsoft open sourced SAI in 2015. This approach enables operators to take advantage of the rapid innovation in silicon, CPU, power, port density, optics, and speed, while preserving their investment in one unified software solution across multiple platforms.

This a great example of SDN solution and how use the power of the hardware layer to provide NVF.

Of course, does not exclude overlay or Network Virtualization solutions, and can be integrated with them (for example is possible to integrate SONiC with VMware NSX).

If you want to test SONiC in a lab, is possible install in GNS3.

For more information see Microsoft official page: https://azure.microsoft.com/en-us/blog/sonic-the-networking-switch-software-that-powers-the-microsoft-global-cloud/