In an OpenFlow network it usually takes two to tango -- an OpenFlow controller and a network switch vendor that supports OpenFlow. But software-defined networking vendor Big Switch Networks hopes to offer its OpenFlow controller customers an unlimited number of dance partners using new network overlay technology.
The new OpenFlow network overlay technology -- part of Big Switch's Big Virtual Switch network virtualization application beta -- lets enterprises build software-defined networks on top of any underlying physical infrastructure, even if it's not OpenFlow friendly.
Specifically, the network overlay technology uses OpenFlow-enabled hypervisor virtual switches at the server access layer of a network to create a virtual network on top of an existing physical network. This network overlay tunnels through the physical network.
"Tunneling from the [server] host lets you keep your existing IP network in place and simply have an overlay," said Joe Skorupa, research vice president at Gartner.
That means that customers can build OpenFlow-based software-defined networks (SDNs) even on top of equipment from Cisco or other vendors that haven't yet made their OpenFlow or SDN moves.
"As long as the first or last hop of every packet is OpenFlow-enabled, we can use this technology to tunnel through the rest of the network," said Kyle Forster, co-founder and vice president of sales and marketing at Big Switch. "You get a lot of the benefit of a [software-defined network]. You can place any virtual machine anywhere regardless of subnets or VLANs, but at the same time you can do it with your existing physical [network]."
Many vendors have introduced tunneling protocols to enable similar network virtualization. Nicira Networks developed Stateless Transport Tunneling; meanwhile, hypervisor vendors are introducing their own tunneling protocols, such as VMware's VXLAN and Microsoft's NVGRE.
Big Switch's OpenFlow network overlay is designed to work with many of these tunneling protocols, allowing customers to have a mixed-vendor, network virtualization environment.
"[Competitors] have a control plane and a tunneling technology that are tightly coupled, so you have to get them from the same vendor," Forster said. "We use OpenFlow, so you can use any tunneling technology you want with the control plane. We are wire compatible with NVGRE and VXLAN."
Downside of an OpenFlow network overlay?
Introducing a network overlay to achieve network virtualization could add management complexity, Forster noted.
"You end up managing two networks, both the underlying physical network and the overlay network," he said. "If something goes wrong, you have two places to check."
Is the pain of managing two networks worth it? Forster said it depends on how many virtual machines a network is supporting. Network virtualization becomes more critical as the number of virtual machines grow.
"We talk to a lot of early adopters who are looking at 2,000 VMs per rack in the next year," Forster said. "As soon as you look at 2,000 VMs per rack, a bunch of other things come along with that. VMs are constantly moving on and off the network, constantly moving between racks, and every other application you have is a disaster recovery plan to span two racks."
Network engineers also might encounter push back from the systems team in data centers, Skorupa said.
"You have to load software onto the servers to do the tunneling," he said. "For example, Nicira provides its own vSwitch. Some folks allow the networking guys to have access to the servers; others, not so much. There will be some enterprises who say, 'I don’t want to further complicate the host.'"
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The first inhibitor to adopting a software-defined network based on OpenFlow is the general lack of switch vendors who support commercial implementations of the technology. Second, there's the cost of installing these new switches.
"We had a lot of folks look at [our technology] and say this solves a ton of my problems, but I have so many other constraints. There's no way I can take out my switches and routers today and [install new OpenFlow devices]," Forster said.
With Big Switch's OpenFlow network overlay, network engineers can migrate gradually. They can implement the network virtualization technology on the entire network, regardless of whether its components support OpenFlow. Over time, engineers can deploy OpenFlow switches into this environment and Big Switch's technology will adapt to the changes. Big Switch only tunnels to non-OpenFlow switches. As an engineering team refreshes elements of a network with OpenFlow switches, Big Switch's technology drops tunnels as they become unnecessary.
Let us know what you think about the story; email: Shamus McGillicuddy, News Director