After Microsoft launched its open source software to run cloud switches, there was a lot of talk about whether this spelled Armageddon for switch manufacturers such as Arista, Juniper, and Cisco.

After all, if Web-scale companies like Microsoft can migrate their switching needs to white-box hardware, running their own open source software, who needs proprietary switches anymore?

Microsoft's Software for Open Networking in the Cloud (SONiC), which came out last week, was developed with the help of several vendors, including Arista, Broadcom, Dell, and Mellanox.

But SONiC is troubling for Arista, according to a research report penned by Jefferies analyst George Notter, who writes that 25 percent of Arista’s revenue comes from giant Web-scale companies including Microsoft, Facebook, and Apple, with Microsoft being "responsible for 12 percent of Arista’s 2015 sales.”

At the Open Compute Project (OCP) conference last week Arista allowed Microsoft to run SONiC on Arista switch hardware without Arista’s EOS operating system.

“Arista has long referred to EOS as their secret sauce and the core value in the company,” writes Notter. “It’s clearly troubling if their largest customer has developed a software suite that is mostly duplicative of EOS’s functionality.”

Juniper and Cisco also receive hefty revenues from switch sales, but Notter writes, “We think the difference between Arista and these other vendors is their degree of exposure.”

He says about 5 percent of Cisco’s overall switching business comes from Internet content providers, and in Juniper’s case, most of its business with the Web-scale giants comes from routing.

As a result of its analysis, Jefferies reduced its price target on Arista shares to $40.25 from $52.50. The report sent Arista's stock down about 10 percent, to $56.53.

When asked if he thinks SONiC spells trouble for switch vendors such as Arista, Dell'Oro Group analyst Alan Weckel, says, “No. I do not.”

“Cloud providers for the most part, outside of Google, have their secret sauce as the control plane, which is abstracted from the actual switches,” says Weckel, adding that this control plane is different from the operating system and is more akin to a software-defined networking (SDN) controller.

“There are millions of lines of code that Arista has written,” he says. “It’s not in anyone’s best interest to replace that. It’s not something that could be done quickly.”

So why is Jefferies so concerned about Arista’s future? “If you look at the sell-side community as a whole, most have a buy rating on Arista,” says Weckel. “Notter is more an outlier view.”

He also looks to salve the nerves of switch makers as far as their hardware is concerned. “When Microsoft comes out with an OCP design, it doesn’t mean it’s a white –box switch from Taiwan. Arista, Dell, or Juniper could build these OCP switches. There’s always some customization that they need.”

That’s probably why Arista is working with Microsoft on SONiC, choosing to partner with its biggest customer rather than resist open source software out of fear of losing switching revenue.