Intra-area LDP Node Protection via Bypass LSP
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Solution Overview
Problem
Traditional link state protocols in computer networks take a long time to adapt to link and node failures, leading to delays in traffic rerouting and potential packet loss due to the need for each router to recompute shortest paths.
Innovation Solution
Implementing a point of local repair (PLR) network device that uses interior gateway protocol (IGP) topology information to automatically establish a bypass label switched path (LSP) and targeted LDP session, allowing for intra-area and inter-area node protection without requiring extensions to the label distribution protocol (LDP).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional link state protocols are used for routing, then routing information can be exchanged and topology can be maintained, but convergence time is long and packet loss occurs during failure recovery
Solution Approach 1:
The patent pre-establishes backup LSPs (Label Switched Paths) and backup next-hop routers before any failure occurs. When a failure is detected, traffic is immediately switched to the pre-computed backup path, eliminating the need to wait for full convergence. This preliminary preparation of alternative routes resolves the contradiction by providing instant reliability while avoiding convergence delays.
Solution Approach 2:
The patent segments the backup path computation into per-area backup paths. Each router computes and maintains backup paths within its own IGP area independently, using IGP topology information. This segmentation allows faster local recovery without requiring global convergence, as each area can independently switch to its backup path using locally available topology data.
2Manufacturing precision
If each router recomputes shortest paths after failure, then accurate routing can be restored, but traffic is dropped during the computation process
Solution Approach 1:
The patent pre-computes backup shortest paths and stores them in forwarding tables before failures occur. When a failure is detected, the system uses the pre-computed backup paths immediately, avoiding traffic drop during recomputation. This preliminary computation of alternative routes maintains both routing accuracy and forwarding efficiency simultaneously.
Solution Approach 2:
The patent introduces backup next-hop routers as intermediaries in the routing path. Instead of directly recomputing paths through the failed node, traffic is routed through pre-identified backup next-hops that serve as mediators, ensuring continuous forwarding while maintaining accurate routing via the backup IGP topology information.
3Speed
If LDP node protection is implemented, then fast reroute is possible, but protocol extensions are required which increases complexity
Solution Approach 1:
The patent makes existing LDP components serve multiple functions: LDP is used both for primary path setup and for discovering backup paths via targeted sessions. The same LDP infrastructure handles both normal operation and failure recovery, eliminating the need for separate backup protocols. This multi-functionality achieves fast reroute capability while avoiding additional protocol complexity.
Solution Approach 2:
The patent uses targeted LDP sessions as intermediaries to discover backup paths. Instead of modifying core LDP, targeted sessions act as a mediator mechanism that leverages existing LDP infrastructure to exchange backup topology information, enabling fast reroute without requiring fundamental LDP extensions or increasing core protocol complexity.
4Loss of time
If backup paths are pre-established, then fast reroute is enabled, but network topology information must be maintained and processed
Solution Approach 1:
The patent computes and maintains backup paths locally at each router using its own IGP topology information. Each router independently manages its backup paths within its area, using locally available data rather than requiring global topology synchronization. This local quality approach reduces the complexity of topology management while enabling fast local response to failures.
Solution Approach 2:
The patent segments topology management by area, with each router maintaining backup paths for its local IGP area using locally obtained topology information. This segmentation isolates topology management complexity to local scope, preventing global complexity propagation and reducing overall system complexity while maintaining fast failure response capability.
Data Source
AI summary
Techniques are described for providing fast reroute intra-area node protection for label switched paths (LSPs) using label distribution protocol (LDP). In one example, a network device may be configured to use network topology information, obtained by an Interior Gateway Protocol (IGP) executing on the network device, to identify a next next hop merge point to which to automatically establish a bypass LSP, and to which to establish a targeted LDP session for obtaining a label advertised by the next next hop merge point.