Non-Forwarding Adjacencies in Clos Network L2 Backbones
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Solution Overview
Problem
Clos networks face scalability issues and L2 backbone partitioning when trying to maintain hierarchical levels and separated areas, with existing solutions either sacrificing scalability or introducing complexities like single points of failure and excessive encapsulation/decapsulation.
Innovation Solution
Establishing L2 tunnels between leaf and ToF nodes to ensure non-partitioned L2 backbone connectivity while identifying these tunnels as non-forwarding adjacencies to avoid using them for traffic forwarding, and leaking L2 prefix information down to L1 to compute routes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If L2 tunnels are established between leaf and ToF nodes to maintain non-partitioned L2 backbone connectivity, then network connectivity is improved, but device complexity and operational complexity increase due to excessive encapsulation/decapsulation
Solution Approach 1:
The patent extracts the tunneling function from the data plane forwarding path and relocates it to the control plane. By identifying L2 adjacencies as non-forwarding, the actual traffic forwarding is taken out of the L2 tunnel path and redirected through L1 routing, eliminating the need for encapsulation/decapsulation in the data path while preserving L2 backbone connectivity for control purposes
Solution Approach 2:
The patent introduces L1 routing as an intermediary mechanism to handle traffic forwarding between leaf nodes. Instead of directly forwarding traffic through L2 tunnels (which would require encapsulation/decapsulation), traffic is routed through L1 routes that leverage the underlying L2 connectivity without requiring tunneling operations at the data plane
2Productivity
If hierarchical levels and separated areas are implemented to improve scalability, then network scalability is improved, but L2 backbone partitioning occurs reducing network connectivity
Solution Approach 1:
The patent segments the network into hierarchical levels (L1 and L2) with separated areas, allowing scalable network growth. L1 handles intra-area routing for scalability, while L2 maintains inter-area backbone connectivity. The segmentation is implemented such that L2 adjacencies are established for backbone connectivity but marked as non-forwarding, allowing the hierarchy to scale without partitioning the L2 backbone
Solution Approach 2:
The patent resolves the connectivity vs. scalability contradiction by operating in two dimensional layers simultaneously: L1 provides the scalable hierarchical structure for area-based routing, while L2 provides the connected backbone dimension for inter-area connectivity. Traffic forwarding occurs in the L1 dimension while L2 maintains the connectivity dimension without being used for forwarding
Data Source
AI summary
Problems associated with providing a large Clos network having at least one top of fabric (ToF) node, a plurality of internal nodes, and a plurality of leaf nodes may be solved by: (a) providing L2 tunnels between each of the leaf nodes of the Clos and one or more of the at least one ToF node to ensure a non-partitioned IGP L2 backbone, and (b) identifying the L2 tunnels as non-forwarding adjacencies in link state topology information stored in ToF node(s) and leaf node(s) such that the L2 tunnels are not used for forwarding traffic. Tunnel formation is prevented over L2.