Recursive FEC mLDP LSP via Remote LFA Node
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Solution Overview
Problem
Current multicast label distribution protocol (mLDP) multicast only fast reroute (MoFRR) systems cannot utilize remote loop-free alternates (LFAs) effectively due to the directly connected upstream LDP neighbor not being an LFA for reaching the corresponding root node, leading to potential rerouting through the link/node to be avoided.
Innovation Solution
A node in the mLDP network determines a remote protecting node and establishes an mLDP label-switched path (LSP) using a recursive forwarding equivalent class (FEC) with the remote LFA node address as the root of the outer FEC and the original root node address as the inner FEC, ensuring the LSP is set up via the remote LFA node, avoiding the protected link/node.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a directly connected upstream LDP neighbor is used for MoFRR, then fast reroute capability is provided, but the neighbor cannot be an LFA for reaching the root node, causing potential routing through failed links
Solution Approach 1:
The patent introduces a remote LFA node as an intermediary protecting node between the downstream LSR and the root node. This remote LFA serves as a mediator that provides loop-free alternate routing capability, allowing traffic to bypass failed links while maintaining proper LSP establishment through the protecting node's involvement in the mLDP signaling process
Solution Approach 2:
The patent extends the traditional two-hop MoFRR architecture by introducing a third dimension - the remote LFA protecting node. This creates a three-node path (downstream LSR -> remote LFA protecting node -> root node) that adds spatial dimensionality to the rerouting capability, enabling loop-free alternates beyond directly connected neighbors
2Adaptability or versatility
If remote LFA is used for protecting node, then loop-free alternate routing is achieved, but the directly connected upstream LDP neighbor is not an LFA for reaching the root node
Solution Approach 1:
The patent performs preliminary actions by having the remote LFA node pre-establish an mLDP LSP to the root node before any failure occurs. The downstream LSR also pre-calculates the remote LFA as a protecting node and prepares the recursive FEC structure, so that when a failure happens, the rerouting can immediately utilize the pre-established path without creating routing loops
Solution Approach 2:
The patent employs nested doll principle through recursive FEC structure where the outer FEC contains the remote LFA protecting node address and the inner FEC contains the original root node address. This nested structure allows the LSP to be established through the remote LFA while ultimately reaching the original root node, combining both protecting node requirements and root node reachability
Data Source
AI summary
In one embodiment, a node in a multicast label distribution protocol (mLDP) network determines a remote protecting node for a particular root node in the mLDP network. In addition, the node determines a protecting node address of the remote protecting node and a root node address of the particular root node, and establishes an mLDP label-switched path (LSP) via the remote protecting node by using the protecting node address as a root of an outer forwarding equivalent class (FEC) of a recursive FEC, and using the root node address as an inner FEC of the recursive FEC for the mLDP LSP. As such, when the remote protecting node is reached, the outer FEC is stripped and the remote protecting node continues establishing the mLDP LSP toward the particular root node.