Autonomous System Backup Path Loop Prevention
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Solution Overview
Problem
Current methods for reducing BGP convergence time in case of inter-domain failures, such as link failures between autonomous systems, still result in unacceptably long recovery times despite techniques like source routing and fast rerouting.
Innovation Solution
Implementing a method to pre-compute backup paths in autonomous systems using protection tunnels with a loop prevention attribute, allowing for immediate rerouting of packets around failed links without requiring cooperation between BGP routers outside the autonomous system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If source routing and fast rerouting techniques are used to reduce BGP convergence time, then packet forwarding speed is improved, but recovery time remains unacceptably long
Solution Approach 1:
The patent pre-computes backup paths and installs them in the forwarding table before any link failure occurs. When a failure happens, the router immediately switches to the pre-computed backup path without needing to recalculate routes, thus achieving fast convergence while avoiding the computational overhead during failure recovery
Solution Approach 2:
The patent implements a dynamic switching mechanism that monitors link status and automatically transitions between primary and backup paths. The forwarding system dynamically adapts to failures by activating pre-prepared backup routes, maintaining high-speed packet forwarding while ensuring rapid recovery
2Loss of time
If backup paths are pre-computed and stored in forwarding tables, then convergence time is reduced, but memory usage and forwarding table complexity increase
Solution Approach 1:
The patent applies backup path computation locally at each router based on its specific topology and failure scenarios. Each router computes and stores only the backup paths relevant to its local context and eBGP peers, rather than maintaining global backup routes, thus reducing memory usage and forwarding table complexity while achieving fast convergence
Solution Approach 2:
The patent extracts and separates the backup path computation from the main routing protocol. Backup paths are computed independently using a simplified algorithm that considers only local topology and IGP metrics, then installed in the forwarding table. This extraction reduces the complexity burden on the main BGP routing system
3Loss of time
If immediate rerouting is implemented upon link failure, then packet loss is reduced, but risk of creating routing loops increases
Solution Approach 1:
The patent implements a feedback mechanism using a loop prevention attribute that is set when packets are rerouted via backup paths. Routers check this attribute to detect and prevent routing loops, ensuring that packets do not circulate indefinitely while still enabling immediate rerouting upon failure. The attribute provides real-time feedback about the packet's rerouting status
Solution Approach 2:
The patent applies preliminary anti-action by pre-configuring backup paths that are guaranteed to be loop-free based on IGP topology properties. The backup paths are computed to satisfy loop-free constraints before any failure occurs, and the loop prevention attribute is pre-set to detect and block any potential loop conditions during immediate rerouting
Data Source
AI summary
A method of implementing a backup path in an autonomous system (AS) for failure of an inter-AS link is described. The method comprises forwarding data elements destined for the failed link via a backup path and including a loop prevention attribute in the packet.