PARIS -- MPLS/SDN/NFV World Congress -- BT's Peter Willis says OpenStack still needs to address two of the six challenges he outlined several months ago before the UK-based operator will feel comfortable about using the technology during a rollout of virtual enterprise CPEs.

Willis, BT Group plc (NYSE: BT; London: BTA)'s chief researcher for data networks, first raised concerns about OpenStack during the SDN & Openflow World Congress held in Düsseldorf last October, threatening to use a proprietary alternative unless the OpenStack community overcame six big hurdles. (See OpenStack Doubts Surface After BT Ultimatum and BT Threatens to Ditch OpenStack.)

His challenges related to the connection of virtual network functions (VNFs), service chain modification, scalability, so-called "start-up storms," the security of OpenStack over the Internet and backwards compatibility.

Speaking in Paris today, during the MPLS/SDN/NFV World Congress, Willis awarded OpenStack a score of four out of six, noting some important technological progress, but continued to sound the alarm bells in the two key areas of backwards compatibility and being able to bind the virtual network interface to the VNFs.

As regards the latter, the problem for Willis is that OpenStack connects VNFs to the infrastructure in a sequential manner. Getting that sequence wrong for a firewall function could be "career-limiting," he says, for a chief information officer.

"It would be good to be able to pass metadata between OpenStack and the VNFs, and then you could perhaps validate the topology, but I've not seen this proposed," he said during a presentation in Paris.

Willis also remains deeply unhappy about the backwards compatibility of OpenStack -- which typically updates every six months -- having previously ruled out any possibility of being able to run the whole network on the same version of the technology.

"It's a major issue for operators because our customers exist in different planned engineering windows and so we can't upgrade all the customers at the same time," he said. "I don't think this has been adequately addressed by OpenStack."

Encouraging signs
In other areas, however, Willis is more optimistic that progress is being made.

BT had previously complained that OpenStack would not allow it to introduce new services for an existing customer without having to problematically disconnect and reconnect interfaces. But a new OpenStack project, described by Willis as sounding like a "good solution," might allow it to connect VNFs to overcome this problem.

Vendors including Huawei Technologies Co. Ltd. and Wind River Systems Inc. have also proposed solutions to the issue of scalability, including putting an OpenStack controller on every node. "That could be a good approach if the controller doesn't consume too many resources," said Willis.

In Düsseldorf, Willis said a single OpenStack controller could be expected to manage about 500 computing nodes, while BT's virtual enterprise scenario would entail managing about 100,000 CPEs.

Another obstacle he discussed at the time was the "start-up storm," which can happen after repairs have been made to a fiber link and thousands of nodes try reconnecting at exactly the same time.

One option that has emerged here is to use random back-up timers. "That would allow controllers to come back in a controlled way, although it would take a bit of time," he told attendees at the Paris conference.

The security of OpenStack over the Internet has also proven to be a headache for Willis, who says he was forced to open up more than 500 pinholes in his firewall to the controller during previous tests.

The answer could involve building a VPN over the Internet, according to Willis. "That seems obvious and straightforward but the issue to bear in mind is how you get encryption keys installed securely on the CPE," he said. "SD-WAN technology might be a solution for that."

For more NFV-related coverage and insights, check out our dedicated NFV content channel here on Light Reading.

Even so, BT does not appear to have completely ruled out using alternatives to OpenStack to overcome some of these challenges.

One of the technologies Willis identified is libvirt, an open source tool for managing platform virtualization that has been developed by Red Hat Inc. (NYSE: RHT).

Although libvirt might help BT address the problem of scalability, it seems unlikely to become a serious option. "You don't want to just push problems further into the orchestration layer or reinvent the wheel," said Willis.

While BT has continued to wrestle with OpenStack, the broader industry has been struggling to reach a consensus on how best to standardize NFV management and orchestration (or MANO).

In February, Light Reading reported on a major split in open source efforts triggered partly by concern regarding the long-term viability of OpenStack. (See Split Emerges in Open Source MANO Efforts and OSM Demos First Steps to Open Source MANO.)

Operators including BT and Spain's Telefónica , which is also thought to have doubts about tying its activities to OpenStack, are now collaborating through the Open Source MANO group, which actually builds on Telefónica's OpenMANO project. Another group, called OPEN-O, is being led by China Mobile Ltd. (NYSE: CHL) and expected to operate out of the Linux Foundation .

Commenting in February on the split, Caroline Chappell, a principal analyst with Heavy Reading , said: "OpenMANO would rather have something that supports hybrid clouds and wouldn't tie very closely to OpenStack, which may not stay the course for the future."

— Iain Morris, , News Editor, Light Reading