When talk turns to flattening the data center network, Cisco has as much of a story to tell as the other guys, if not more so.

"In our conversations with customers, we talk about the importance of decoupling physical tiers from logical tiers in terms of design, traffic and engineering efficiencies," says Omar Sultan, a marketing manager with Cisco's Data Center Solutions (DCS) group.

"When you've got things like live migration of virtual machines and scale-out enterprise application architectures going on in your data centre, flattening the network makes sense," Sultan says. "Supporting those types of traffic flows start to require a big, fat, Layer 2 domain, with lots of bandwidth and deterministic latency between the servers."

And when you're talking "big, fat, Layer 2 domains," you've got to diverge from a tried-and-true network technology – namely Spanning Tree Protocol (STP). Cisco has that covered in the NX-OS operating system software for its Nexus switches, with technologies such as virtual PortChannel (vPC), FabricPath and Overlay Transport Virtualisation (OTV), Sultan says.

A NX-OS trio

VPC, which allows the spanning of port channels across two switches, was Cisco's early attempt to address the limitations of STP. More significant differentiators are the newer FabricPath, due this quarter, and OTV, available now.

FabricPath, an early implementation of the Transparent Interconnection of Lots of Links (TRILL) standard under development within the IETF, provides a way to scale data centre fabrics by merging Layer 2 switching and Layer 3 routing. With FabricPath comes the elimination of STP and reduced latency as server-to-server traffic moves over multiple active links

"We consider this a key enabling technology for allowing enterprises to build very large, scalable networks. FabricPath literally will let them run thousands and thousands of 10G servers in a single, large, flexible Layer 2 domain," says Nikhil Kelshikar, also a DCS marketing manager at Cisco.

OTV, meantime, lets enterprises interconnect Layer 2 networks, whether those networks are in the same data centre or at different locations. This is essentially a Nexus-only tunnelling technology, allowing passage for Layer 2 Ethernet frames through a Layer 3 infrastructure. "You're effectively creating a virtual private cloud," Sultan says.

This is the sort of capability John Turner, director of networks and systems at Brandeis University, in Waltham, Mass., says he's looking for. In fact, he says, it's one of two top criteria he has for selecting his next data centre switches, a process he's currently undertaking.

"The vendor has to meet our business objective, which is to connect multiple data centres together and be able to create a Layer 2 network over a long-distance path and complete the migration of virtual machines with available bandwidth and over distance," he says.

OTV will help Cisco fulfil its bigger data centre vision of enabling access to a pool of data centre resources, Sultan says. "It's an enabling technology as it'll pull data centres together and let workloads run back and forth."

Think logically

Using technologies like vPC, FabricPath and OTV, Cisco encourages enterprises to think about a flatter network architecture.

"The biggest reasons people build more tiers is to manage performance and over subscription. Clearly as we've evolved and introduced technologies like FabricPath, we can start shrinking the number of tiers because we can reduce over subscription," Kelshikar says. "But at the same time, the other reason for building hierarchical networks is to do fault isolation or provide segmentation across multiple different customers – and that's more of a logical construct. That logical hierarchy will not go away."

So Cisco's guidance for enterprises is to take advantage of a flattened network opportunistically. "They should deploy a flatter network where it makes sense and leverage existing infrastructure where that makes sense – and the nice thing is they can migrate in a granular fashion from a three-tier architecture to a flattened, two-tier or smaller architecture as they have business drivers," Sultan says.

This, of course, presumes use of the Nexus switches. Customers who have the earlier Catalyst switches, which rely on the IOS operating system, do not have the new networking technology options available with the Nexus line.

Still, even if you're talking about changing out switch lines, Cisco does come with one advantage for many data centre network managers – familiarity, Turner says. And, with its year-old Unified Computing System (UCS), which integrates blade servers with storage access, virtualisation and switching, Cisco can tell a good integration and management story, he says.

"What Nexus potentially gives us down the road are easier upgrade, management and integration paths, plus it will integrate with our Fibre Channel storage when we need to do that. Nexus is the story of complete integration. But it also could be about single point of failure, so we've got to consider that, too," he says.

Still, in terms of flat network positioning today, Cisco's ability to tell the story not only from the networking side but also from the server and storage aisles is giving it considerable market influence, says Tom Nolle, president of CIMI, a technology assessment firm.

A recently completed CIMI survey shows Cisco having the largest strategic influence gain of any vendor, Nolle says.

"This isn't because it's doing anything better on the networking side, but because it has server technology and can talk about the data centre architecture at a higher level than competitors," he explains. "Its scope has broadened, and its sales force does a better job than anybody else's in explaining what this all means for customers."

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Ultimate guide to the flat data centre network