March 29, 2012, 8:58 PM — Cisco's FabricPath data center Ethernet technology is designed to combine traditional, Spanning Tree-based Ethernet with a next-generation architecture that uses a link-state protocol to allow for multiple active paths. Deploying multiple active paths in a data center network is required to flatten the infrastructure to reduce latency and better support traffic flow between server racks.
The following attempts to boil down the key aspects of FabricPath on a Cisco Nexus 7000 core data center switch, as described in a Cisco whitepaper. Several features of FabricPath are vital to its operation, including:
• Replacing Spanning Tree with a link-state protocol;
• Interacting with Spanning Tree domains;
• Use of virtual PortChannel (vPC) to activate parallel paths and remove Spanning Tree blocks;
• Defining processes as virtual device contexts (VDC);
• Conversational MAC address learning and use of switch IDs (SID), and;
• VLAN designations
A-MAZE-ING: Figuring out the data center fabric maze
Use of a link-state protocol
Using or replacing Spanning Tree with a link-state protocol is intended to overcome the limitations of Spanning Tree in data center and cloud environments - chiefly, the inability to use multiple active parallel paths in an Ethernet network. Spanning Tree allows only one path to be active between any two nodes and blocks the rest, which is unsuitable for low latency, Ethernet-based fabrics in data centers and cloud environments.
Virtually every vendor addressing the data center fabric switching market proposes augmenting or replacing Spanning Tree with a link-state protocol, and standards like TRILL and Shortest Path Bridging are being defined to do just that. Brocade uses TRILL in the data plane of its VCS architecture but the control plane is based on Fabric Shortest Path First, an ANSI standard used by all Fibre Channel SAN fabrics as the link-state routing protocol.