IS-IS Flood Reflector Path Computation for LSP Establishment
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Solution Overview
Problem
In IS-IS FR networks, L2 nodes and L1 nodes cannot directly communicate, making it impossible to establish an optimal LSP that satisfies traffic engineering requirements across the network.
Innovation Solution
A head L2 node determines an end-to-end path from itself to a tail L2 node within the IS-IS FR network, which includes multiple FR clusters. The head L2 node then sends information associated with this path to other nodes to establish a label-switched path (LSP) that traverses one or more L1 links within the FR clusters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If L2 nodes and L1 nodes cannot directly communicate in IS-IS FR networks, then network structure is maintained, but optimal LSP establishment across FR clusters becomes impossible
Solution Approach 1:
The patent introduces L1/L2 border nodes as intermediaries that can communicate with both L1 nodes (within FR clusters) and L2 nodes (across the backbone). These border nodes act as mediators that translate and relay path computation information between the two levels, enabling end-to-end path determination across FR clusters while maintaining the hierarchical isolation of the IS-IS FR architecture.
2Adaptability or versatility
If direct communication between L2 nodes and L1 nodes is prohibited, then hierarchical network structure is preserved, but traffic engineering capabilities are lost
Solution Approach 1:
The patent segments the path computation function into two parts: L2 nodes compute the end-to-end path at the L2 level (across FR clusters), and L1/L2 border nodes compute the detailed intra-cluster paths at the L1 level. This segmentation allows traffic engineering capabilities to be introduced without requiring full integration between L1 and L2 domains, thus maintaining architectural simplicity while enabling adaptability.
Solution Approach 2:
The patent adds a new dimension to path computation by operating at multiple hierarchical levels. Instead of a single flat path computation approach, the solution computes paths in two dimensions: first at the L2 inter-cluster level, then at the L1 intra-cluster level. This multi-dimensional approach enables traffic engineering across FR clusters while respecting the hierarchical network structure.
3Productivity
If LSP traversal across FR clusters is not supported, then network simplicity is maintained, but optimal routing paths cannot be established
Solution Approach 1:
The patent performs preliminary path computation at the L2 level before actual LSP establishment. The L2 node first determines the end-to-end path through FR clusters using RSVP-TE signaling, then this pre-computed path information is used by L1/L2 border nodes to establish the detailed LSP segments within each cluster. This preliminary action enables optimal routing without requiring complex real-time computation across all nodes during LSP establishment.
Data Source
AI summary
In some implementations, a head Level 2 (L2) node of an intermediate system-intermediate system (IS-IS) flood reflection (FR) network may determine an end-to-end path from the head L2 node to a tail L2 node of the IS-IS FR network. The IS-IS FR network includes a plurality of L2 nodes and a plurality of FR clusters that each comprise a plurality of Level 1 (L1) nodes and a plurality of L1 and L2 (L1/L2) nodes connected by a plurality of L1 links. The head L2 node may send information associated with the end-to-end path to another node identified in the end-to-end path to cause a label switched path (LSP) to be established from the head L2 node to the tail L2 node, wherein the LSP traverses one or more L1 links within an FR cluster of the IS-IS FR network.