LDP Fast Reroute Backup Path Label Stacking
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Solution Overview
Problem
Current MPLS Fast-Reroute techniques, such as LDP and RSVP-TE, face challenges in achieving fast convergence due to IGP convergence limitations and complex configuration requirements, leading to slow failure detection and re-routing in carrier-class networks.
Innovation Solution
The implementation of LDP Fast-Reroute using backup shortest path LSPs, where a backup path is created from the Point of Local Repair (PLR) to a Backup Shortest Path Merge Point (BSP-MP) to reroute traffic around potential failures, utilizing label stacking to switch traffic from the shortest path LSP to the backup LSP without requiring additional state along the path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LDP follows routed paths setup by IGP to establish LSPs, then the LSP convergence is gated by IGP convergence, but IGP convergence is traditionally slow due to detection time, reaction time, transmission time, re-computation time, and download time
Solution Approach 1:
The patent segments the LSP establishment process from IGP convergence by using LDP to independently set up Label Switched Paths that do not necessarily follow IGP routed paths. This allows LSPs to be established and converged separately from the IGP routing process, bypassing the slow IGP convergence bottleneck while maintaining network reliability.
Solution Approach 2:
The patent introduces LDP as an intermediary protocol between the control plane and data plane for LSP establishment. Instead of relying on IGP to directly control LSP paths, LDP acts as a mediator that can independently allocate labels and establish LSPs along optimized paths, thereby decoupling LSP convergence from IGP convergence and enabling faster recovery.
2Reliability
If RSVP-TE is used as a failure-bypass mechanism for LDP LSPs, then FRR capability is provided, but extensive configuration and maintenance experience requirements increase operating expenses
Solution Approach 1:
The patent makes LDP universal by enabling it to provide both normal LSP establishment and Fast Reroute capabilities within a single protocol framework. Instead of requiring separate RSVP-TE infrastructure for FRR, LDP is enhanced to handle both functions, eliminating the need for dual protocol support and reducing operational complexity while maintaining failure recovery capability.
Solution Approach 2:
The patent enables LDP to self-configure backup paths and perform automatic failure detection and rerouting without requiring extensive manual configuration or specialized maintenance expertise. The protocol autonomously manages label allocation, path computation, and failure recovery, thereby reducing operating expenses and easing operational burden.
3Ease of operation
If LDP is used instead of RSVP-TE, then simplicity and wide adoption are maintained, but FRR capability is limited by IGP convergence speed
Solution Approach 1:
The patent introduces dynamics into LDP by enabling it to adaptively respond to link failures through Fast Reroute mechanisms. LDP dynamically detects failures, computes alternative paths, and reallocates labels in real-time, transforming LDP from a static protocol bound by IGP convergence into a dynamic protocol capable of independent fast recovery while maintaining its simplicity and widespread adoption.
Data Source
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AI summary
A first network element in an MPLS network receives a first label advertised from a second network element in the network. The first network element computes a shortest path tree (SPT) to reach a destination network element under a potential failure condition. The second network element is a nexthop of the first network element in the computed SPT and is not upstream from the potential failure condition in the computed SPT. The first network element determines that a third network element in the network is a Point of Local Repair (PLR) when the potential failure condition is realized. The first network element distributes a second label to the third network element for a backup LDP Label Switched Path (LSP) that will serve as a backup path when the potential failure condition is realized. The first network element installs a swap action from the second label to the first label.