Brocade: Some OpenFlow switches can't operate at line-rate speeds

While unveiling its WAN-focused software-defined networking strategy, Brocade revealed that competitors are selling OpenFlow switches that can't operate at line-rate speeds.

In outlining its software-defined networking strategy Brocade has exposed a dirty little secret about some commercial OpenFlow switches: Once OpenFlow is turned on, some competing switches no longer operate at line rate. If this is true, network engineers will have to dig deeper into OpenFlow switch specifications to determine actual speed.

Brocade highlighted speed as a differentiating factor in its software-defined networking strategy. That strategy includes support for OpenFlow on the MLX router series with MLX version 5.4, which can move packets at 100 gigabit line-rate speeds.

"We've implemented OpenFlow in our programmable hardware accelerators on a line-card-by-line-card basis. If you've taken a shortcut and enabled OpenFlow so that it is just operating on your management processor -- in other words not in hardware -- then you have to run all your packets through that management processor. Those things are relatively low-performing," said Keith Stewart, Brocade's director of product management. In this case, with OpenFlow turned on, performance drops from gigabits- to megabits-per-second, he added.

Which vendors have troubled OpenFlow switches?

Forrester Research senior analyst Andre Kindness confirmed the speed issue and the idea that the problems are linked to OpenFlow switches that rely on software implementation of the protocol.

"It’s a dirty little secret in the industry," said Kindness. "Take a look at the switches that have come out, even HP's switches. They are supported by firmware but not really running through the ASIC [in all cases]. If it's not hardware, it's not line-speed."

HP Networking does implement OpenFlow in its ASICs, but due to hardware limitations common among many vendors, OpenFlow controllers can overwhelm those ASICs by sending more rules to a switch than it can fit in its flow processing tables. When that happens, those extra flow rules spill over and are handled in software instead. This slows down the switch.

"The flexibility and power of the OpenFlow protocol allows for very large types of flow processing matches and actions; as such, there are possible cases in which not all of these are processed at line rate in every situation," said Charles Clark, distinguished technologist, HP Networking, in a statement. "HP's OpenFlow implementation has been optimized to accelerate those aspects of the OpenFlow protocol that are needed to deliver solution performance and scalability."

Brocade claims that its implementation of OpenFlow on the MLX does not suffer from this problem. 

To get line-rate performance out of Openflow switches, vendors must implement OpenFlow in their ASICs, not their network operating systems, said Nick Lippis, CEO at consultancy Lippis Enterprises.

"I haven’t done the testing, but I do know there are a few [OpenFlow switches] out there that" don’t operate at line-rate speeds, Lippis said.

The whole issue could go away, however, when merchant silicon vendors start supporting OpenFlow on their own chips by the end of this year.

Brocade's software-defined networking strategy

Beyond speed, Brocade's software-defined networking strategy uniquely focuses on wide area networks (WANs) and service provider networks rather than data center and campus networking. That's why Brocade's initial OpenFlow support is available on the MLX router. Google revealed last month that it had built a multi-data-center, software-defined WAN using OpenFlow.

Most other vendors are more focused on using OpenFlow in the data center even though the technology is not fully baked. Meanwhile, carriers that are focused on heavy traffic can begin using the technology today.

More on software-defined networking and OpenFlow

Switch vendors must play nice with OpenFlow controllers

HP OpenFlow: Escape from the tyranny of CLI

Software-defined networking should focus on Layer 3, not Layer 2

"Carriers are hot on this because it allows them to go from dumb pipes to offering different levels of SLAs," Kindness said. "Today they offer SLAs, but they can't really guarantee it and give definitive variations between customers. They can start doing that with what Brocade is opening up."

Brocade's software-defined networking strategy also encompasses a broad range of technologies and vendor partnerships. Brocade unveiled a formal relationship with NEC, using its ProgrammableFlow OpenFlow controller. IBM has a similar relationship with NEC.

Brocade will also support network virtualization via overlay protocols, such as VXLAN, NVGRE and STT. Additionally, it will provide integration into various cloud orchestration and management systems, such as Cloudstack, OpenStack, Microsoft System Center and VMware vCloud Director.

OpenFlow infrastructure in hybrid mode

With Brocade's OpenFlow implementation, network engineers will be able to operate MLX routers in OpenFlow hybrid mode, allowing the use of a combination of OpenFlow and traditional forwarding techniques on the same hardware.

"In a lot of other cases, when you turn on OpenFlow, you turn off all traditional forwarding. We've heard from a lot of customers that baseline forwarding works just fine. What they want to do is layer services on top of it that offer value," said Stewart.

"Some of the research networks [with which] we have been working very closely, are interested in running a traditional backbone in hybrid mode, where traditional forwarding works like it always does, with BGP, OSPF, IS-IS, but then you can allow researchers to provide experimental network applications that run via OpenFlow on that production environment on a subset of traffic."

Hybrid OpenFlow mode will hold appeal beyond research networks as well, Kindness said.

"If you have 20 to 80 applications, are you worried about all of those, or are you most concerned with maybe one or two that are a business priority?" he said, adding that in hybrid mode, enterprises can allow most applications to run via traditional forwarding while using software-defined networking to prioritize those select critical applications.

Let us know what you think about the story; email: Shamus McGillicuddy, News Director

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