Glue Networks is announcing Wednesday that it's raised $12.4 million from unnamed private investors, continuing the 6-year-old startup's non-venture-capital growth curve.

Glue's first funding — $4.5 million at the end of 2010 — came from angel investors.

The company's software is running in carrier networks, partly because it's had Cisco as an ally. Cisco made that relationship official a week and a half ago by officially starting to resell Glue's software, Glue CEO Jeff Gray says.

You might recognize Glue's name from the recent DemoFriday™ with Cisco. But that was mostly about Cisco's onePK architecture for software-defined networking (SDN) and only showed a sliver of what Glue actually does, Gray says.

Glue's gluware software automatically turns up and provisions remote sites by applying policy-based configuration in real time, but it also goes beyond that by checking policies iteratively against an expert system. This makes for dynamic network control, a WAN that can adapt to changes in the network. That's atypical for the WAN, where configuration is assumed to be set in stone, Gray says.

After starting in 2007, Glue made two central decisions: focusing on the WAN (because enterprise traffic was growing and the WAN seemed like a bottleneck in the making), and avoiding publicity until a solid product was available, rather than doing the usual dance of revealing architectures and "vision."

That's all very admirable, but none of it was likely to come to anything unless Glue could work its way into carrier networks. The relationship with Cisco has been the key there. Glue got its first customers with the help of resellers, but sometime fairly early in its life, it also nabbed Cisco as a collaborator through personal connections of Gray's and of his co-founder, CTO Olivier Huynh Van.

Gray doesn't want to discuss how all of that came about, but in any event, Glue did get its products into service providers for trials. Often, it started by applying the software just to an executive's home office — "a branch of one," Gray says. That gave Glue the opening to show it was providing a cheaper and more flexible alternative to a WAN strung with MPLS and private lines.

Naturally, Glue wants to use its new $12.4 million for growth. Gray isn't saying how many people Glue employs, but he expects to add more than 30 during 2014.