The Spanning Tree Protocol (STP) is a long standing standard for networking that has come under fire in recent years. Spanning Tree doesn’t meet the demands of cloud scale and it doesn’t deliver the latency characteristics that many companies want from large multi-chassis networking deployments. It’s a challenge that was debated this week, during a panel discussion at the Interop conference.
One way to avoid the challenges of Spanning Tree, suggested by panelist – Francois Tallet, Product Manager, Nexus 7000 at Cisco, is to simply connect the network together with a single switch. That type of deployment only works with large boxes like the Cisco Nexus switch that can scale to up to 768 ports.
“Most people don’t want to just rely on a single box,” Tallet admitted. “In a distributed model with multiple boxes there is more stability for troubleshooting.”
That’s where a solution like Cisco’s FabricPath comes in. FabricPath’s goal is make a network look like a single switch, eliminating the need for spanning tree since traffic is all routed inside of the Fabric.
Tallet noted that FabricPath is a pre-standard implementation for TRILL (Transparent Interconnection for Lots of Links). TRILL is a broader industry effort that is currently undergoing its own standardization process. According to Tallet, what FabricPath adds on top of TRILL is more active interaction with Layer 3. He noted that in TRILL today, the draft specification only enables networks to route from a single active gateway. He stressed that Cisco is pushing that innovation back into the standard and at some point both will converge.
The other key alternative to Spanning Tree is Shortest Path Bridging. Panelist Paul Unbehagen, Director, Strategy and Standards at Avaya is also the co-author of Shortest Path Bridging standard. In his view, SPB makes the most sense as it’s an evolution of existing IEEE and IETF standards.
“There are only two protocols that matter, IP and Ethernet,” Unbehagen said.
In his view, there are only so many ways that you can design IP and Ethernet to work together. What SPB does is it combines the effectiveness of MPLS with effectiveness of Ethernet. He stressed that the SPB standard was jointly developed by both the IEEE and IETF. SPB has all advanced IP knowledge of MPLS and is backwards compatible with Spanning Tree.
According to Unbehagen, IEEE is very stringent when it comes to backwards compatibility. That means that any new standard can’t orphan anything that has been in the last 40 years of Ethernet standards.
“That means that everything IEEE produces just works,” Unbehagen said.