All the people who thought Embrane would eventually get acquired by Cisco now have a little more fuel for that argument.

Gigaom reported Thursday morning that Embrane has picked up a $12 million round of funding, about $6 million of it from Cisco.

This appears to be the Series C round that Embrane was awaiting in November. It would bring Embrane's funding total to about $39 million.

Embrane was early to target Layer 4-7 functions in software-defined networking (SDN), creating a platform for service chaining. Embrane provides some of the pieces you'd want to chain together — firewalls and load balancers, for instance — but it's the platform, named heleos, that would make Embrane special.

The Layer 4-7 angle makes sense (we're supposedly doing all this SDN work for the sake of applications, after all) and has attracted the bigger players, as you'd expect. Citrix recently added Palo Alto Networks' firewalls as an option for its SDX platform for virtual application delivery controllers (ADCs). And F5 launched its Synthesis architecture in November, creating what it calls a Layer 4-7 fabric.

Security, in particular, is a Layer 4-7 function that everybody says is paramount for SDN's future. But if security is such a big deal, why is a company like Embrane having trouble gaining any traction?

We don't have a complete answer to that yet. SDN security is likely to be a huge topic at the RSA Conference at the end of February, but I expect that the question of how to deliver security is going to linger for a long time.