Loop-Free Alternate Repair Path Computation

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Solution Overview

Problem

In data communications networks, loops can occur during routing transitions due to temporary desynchronization of link state databases and forwarding information, leading to packets being endlessly forwarded without reaching their destination.

Innovation Solution

A method and apparatus for forwarding data that computes a repair path around a failed component using a network interface, logic to receive a repair address, and propagate it along a label switched path, reducing unnecessary computations and preventing loops by using incremental shortest path first processes and loop-free alternate paths.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If link state protocol is used for routing, then routing information is synchronized across the network, but loops can occur during routing transitions due to temporary desynchronization

Engineering Contradiction:

Improverouting information synchronizationVSAvoidforwarding loops

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent pre-computes loop-free alternate (LFA) repair paths and stores them in the forwarding information base before failures occur. When a link state change is detected, these pre-computed repair paths are immediately activated to prevent loops, rather than waiting for SPF recalculation to complete.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent introduces repair paths as intermediary forwarding routes that activate during transitions. These repair paths serve as temporary mediators that bypass the desynchronized state where loops could occur, allowing packets to be forwarded safely until normal SPF routing is re-established.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If SPF algorithm is used to compute optimal routes, then shortest path routing is achieved, but computational overhead increases during network changes

Engineering Contradiction:

Improverouting efficiencyVSAvoidcomputational time during transitions

Core Design Contradiction:

ProductivityVSLoss of time

Solution Approach 1:

The patent pre-computes and stores LFA repair paths in the forwarding information base during normal operation. When failures occur, these pre-computed paths are immediately activated without requiring time-consuming SPF recalculation, thus maintaining routing efficiency while minimizing computational overhead during transitions.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Instead of performing full SPF recalculation across the entire network topology during every link state change, the patent computes only the necessary LFA repair paths for affected destinations. This partial computation approach reduces the computational burden while still providing adequate routing coverage.

Inventive Principle:

Principle #16Partial or excessive action

3Ease of operation

If normal forwarding is used during routing transitions, then forwarding simplicity is maintained, but packets may be forwarded in loops indefinitely

Engineering Contradiction:

Improveforwarding simplicityVSAvoidpacket delivery guarantee

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent pre-computes LFA repair paths and stores them in the forwarding information base alongside normal routing entries. During failures, packets are automatically redirected to these pre-computed repair paths without requiring complex real-time loop detection or complex forwarding logic, thus maintaining forwarding simplicity while guaranteeing loop-free delivery.

Inventive Principle:

Principle #10Preliminary action

4Reliability

If LFA repair paths are pre-computed and stored in FIB, then loop-free forwarding is achieved during failures, but forwarding table complexity increases

Engineering Contradiction:

Improveloop-free forwardingVSAvoidforwarding table structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent stores LFA repair path information locally in the forwarding information base at each router, rather than requiring global coordination or complex distributed algorithms. Each router independently maintains its own repair paths to neighboring routers, simplifying the overall system complexity while ensuring loop-free forwarding.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS9350639B2Forwarding data in a data communications network

Publication Date: 2016.05.24 CISCO TECHNOLOGY INC

AI summary

In an embodiment, an apparatus for forwarding data in a data communications network having as components nodes and links therebetween comprises a network interface configured to couple to a data communications network having as components nodes and links therebetween; first logic which when executed is operable to receive a repair address; second logic which when executed is operable to compute a repair path from a repairing node to the repair address around a failure component on a primary forwarding path between the apparatus and a repairing node; and third logic which when executed is operable to propagate the repair address along a label switched path (LSP), comprising the repair path, to the repairing node. The apparatus offers improved efficiency in computing a repair path in a network around a failed component because unnecessary computations are not performed with the disclosed apparatus and approach.