Juniper Calls Time On Spanning Tree Protocol

New network architectures will simplify data centres and eliminate the hated spanning tree protocol, says Juniper – a goal which Cisco is also approaching from a different direction.

Juniper Networks’ Project Stratus, due in 2011, will “flatten” data centre networks to a single data plane, and the company says it will do away with Spanning Tree, a clumsy protocol designed to cope with the complexities of multi-layer networks. Cisco has promised the same thing – but the two companies are taking a different approach, says Juniper.

Shortfalls of tree structure

“I have yet to meet a customer who likes running Spanning Tree. I can eliminate the need to do that altogether,” claimed Andy Ingram, Juniper’s VP of marketing for fabric and switching, at an analyst event in San Jose.

According to Ingram, in a tree structure, 30 to 50 percent of the ports connect switches to other switches – “not servers to the network, not storage to the network, not users to the network”. Unfortunately, he explained, these are the most expensive ports in the data centre.

In Ethernet, loops are not allowed, so any links that cause loops are blocked off, explained Ingram  – effectively reducing the bandwidth of the network by half. “There’s something architecturally defective with that concept,” he said. “Maybe it’s good for vendors – it’s not good for customers.”

Moreover, as Juniper CEO Kevin Johnson stated in his keynote, in the legacy network approach, every time you double the number of storage and servers in the data centre you have to quadruple the number of switch cores. “That means the complexity is growing exponentially as these servers get consolidated,” said Johnson.

Juniper proposes to tackle these problems with its 3-2-1 roadmap, which is currently seeing data centre networks reduced from three tiers (access, aggregation and core) to two tiers, by removing the aggregation layer with its Virtual Chassis. This will eventually collapse down to one layer with the introduction of Juniper’s much-trumpeted Project Stratus – scheduled for 2011.

A single layer means no loops?

While Juniper has so far not revealed the details of this final solution, Ingram says it will consist of a single-layer network fabric that connects all the devices in the data centre. It will run Juniper’s Junos operating system and will be managed through a single control interface.

“By our definition Stratus is a fabric. A network fabric takes multiple physical devices and ties them together with the data plane and the control plane so they behave as a single logical device, a single logical switch,” said Ingram. “And you get the best of both worlds – the performance and simplicity of a switch and the scalability and resiliency of a network.”

Juniper is not the only networking company to be talking about flatter networks and fabrics in the data centre. The FabricPath Switching System (FSS), for example, is the foundation of a push by Cisco to build the next generation of high-performance network systems, and it too claims to eliminate the need for Spanning Tree Protocol.

According to Juniper, however, none of its competitors have quite the same understanding of network fabrics as it does.

“What they’re trying to do is take multiple of their switches, and link them together in a way that they behave coherently like a fabric,” explained Ingram. “With Stratus we are building a fabric that will behave like a single switch.

“So when we say fabric we mean something very different than when other people seem to be saying fabric,” he added. “I like the direction that they’re headed, I’m just not quite sure that their approach is the same as ours.”