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Shortest Path Bridging: The interoperable alternate to spanning tree?

An Interop 2012 panel on spanning tree protocol alternatives quickly evolved into a debate about Shortest Path Bridging as an interoperable solution.

LAS VEGAS -- There is one unifying theme among the alternatives to spanning tree protocol currently proposed in the networking industry: they lack interoperability. But Shortest Path Bridging (SPB) could offer up an interoperable alternative.

At this point, vendors are using a range of proposed protocols, from Transparent Interconnection of Lots of Links (TRILL) to Multichassis Link Aggregation (MLAG), that don't play nicely together. Even the companies using TRILL are implementing different iterations that can't interoperate. This may be why a vendor panel at Interop 2012, "Alternatives to the Spanning Tree Protocol," quickly turned into a discussion about SPB.

SPB is the pending IEEE standard based on the IS-IS protocol that promises to be a standards-based approach to enabling Layer 2 multi-pathing. Unlike competing protocols, SPB is backward compatible, so it interoperates with standard Ethernet and Internet Protocol (IP) without requiring a hardware upgrade. 

But SPB isn't the most heavily used protocol at this point. Today Avaya is the highest profile networking vendor supporting SPB while most others have pursued TRILL, a technology also based on IS-IS that the IETF is standardizing. Alcatel-Lucent and Huawei also support SPB and Enterasys Networks has SPB in its roadmap. 

At Avaya, SPB is being deployed today in production environments and can work on any device that supports IP and Ethernet, as long as the vendor decides to support it, said Paul Unbehagen, director of PLM strategy and standards for Avaya, and an engineer deeply involved in the development of the SPB standard.

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Meanwhile, Cisco has based its FabricPath technology on TRILL, while Brocade has used TRILL as a foundation for its Virtual Cluster Switching (VCS) technology. But the companies are not using interoperable implementations of TRILL.

Extreme Networks promotes MLAG as a technology that can eliminate spanning tree today, while Juniper Networks has eliminated spanning tree protocol by abandoning Ethernet. Its QFabric technology turns many switches into a large abstracted switch, separating the control, management and data planes into various devices.

The vendors all presented their strategies at the Interop panel, but every single attendee question was devoted to SPB: Is it really in production today? How do you manage it? The question that stirred the most discussion was, Will other vendors on the panel support it?

Kishore Inampudi, senior product marketing manager for Juniper Networks, offered a nuanced answer to that question.

"The way we look at it, we see it as system-level interoperability," he said. In other words, Juniper will interoperate with anything at the edge of QFabric, but QFabric itself will exist in a data center as its own cloud with very granular internal management.

Cisco was even less giving on the future of SPB. Francois Tallet, product manager for the Nexus 7000, said flatly, "Cisco is backing TRILL."

While Extreme Networks emphasizes MLAG as an alternative to spanning tree protocol, the company is considering both SPB and TRILL. "It depends on what problem you are trying to solve," said Shehzad Merchant, vice president of technology. "We don't view this as a religious argument. I think over time the space will evolve, and people will have multiple solutions."

For users, the lack of interoperability means a nightmare of vendor lock-in. CGGVeritas, an international geophysical company offering technology services and equipment in the global oil and gas industry, has been using OSPF. But, said Doug Northrup, manager of its global network group, "there’s no management."

Northrup had been waiting for TRILL to catch on, but the proprietary technologies that have hit the market aren't much help.

"I need a standard from TRILL, not just a version of TRILL. I can't go with a single vendor with all the mergers and acquisitions [we've had]," he said. CGG's environment has equipment from Force10 Networks, Arista Networks, HP Networking, Extreme Networks and Blade Network Technologies (now part of IBM). As for SPB, Northrup is waiting to gauge vendor support.


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

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