HP just teamed up with a startup that's in the swarm of sharks circling Cisco

Cisco seems intent these days on taking down Arista Networks, an upstart rival founded by a bunch of ex-Cisco execs. But there's another startup founded by a different bunch ex-Cisco people that could soon become a bigger threat.

On Thursday a startup called Cumulus Networks announced a huge partnership with HP.

HP has agreed to sell a product called a "data center network switch" that is based on Cumulus's software. These switches will not be made by HP. They will be produced by a Taiwanese contract manufacturer, Accton Technology.

It's a big deal because this partnership combines, in one fell swoop, all the things that are threatening Cisco: some of its most bitter competitors, and a new less-expensive way to build networks using open source software.

Cisco pretty much owns the computer network equipment market, with a good 60% market share on just about every type of equipment used to build networks. In the sub-category where Cumulus plays, network switches for huge data centers, Cisco is far and away the leader with about 67%, next to Arista Networks' 8%, according to Crehan Research.

Arista's star is rising. It just claimed Facebook as a customer, even though Facebook is also building its own new computer network hardware and sharing those designs with anyone that wants to copy them. A few months ago, Cisco sued Arista, and although that muddies the waters, Arista is expected to post extremely strong revenue growth on Thursday, up by 45%.

HP has no intention of letting either Cisco or Arista walk away with this hot up-and-coming market.

So it cozied up with Cumulus Networks, a startup founded by former Cisco engineering fellow JR Rivers in 2010. A Cisco Fellow is the highest technical achievement an Cisco engineer can earn.

Rivers also worked on Nuova Systems, one of Cisco's legendary "spin-ins." That was the team that made Cisco's server product, which is selling well against HP's servers.

The switch involved in this agreement is not based on Facebook's newfangled computer networking designs. However all three of these companies - Cumulus, HP and Accton Technology - are heavily involved in Facebook's Open Compute Project, the umbrella organization under which a lot of new hardware is being designed. Both HP and Accton are contract manufacturers that produce all sorts of OCP hardware.

To top it off, Cumulus' software works with VMware's NSX software, a competitive product that is trying to make Cisco's gear obsolete.

Cisco isn't in immediate danger. Companies do not lightly jump ship from one network equipment vendor to another. HP has been trying to beat Cisco for years and it hasn't happened yet.

But Cisco is increasingly surrounded with new technologies, new partnerships among its rivals, and new startups, many of them founded by former Cisco bigwigs.

Cisco CEO John Chambers has an answer for rivals like Cumulus and Facebook. Last week during Cisco's quarterly earnings conference call, he vowed to "crush" them while "having fun" beating VMware.