MPLS Control Plane Forwarding State Verification

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Solution Overview

Problem

In MPLS Traffic Engineering, synchronization issues between the forwarding and control planes can lead to unreliable data transmission and failure in Fast Reroute protection, as the control plane may not detect corrupted forwarding tables, causing traffic to be rerouted onto faulty backup tunnels.

Innovation Solution

Implementing a method to verify the forwarding state of MPLS Traffic Engineering LSPs and Fast Reroute tunnels, using a new bit in the RSVP RESV message ('Local Protection Status Verified') to inform the control plane of forwarding plane anomalies, allowing for rerouting or notification of issues, thereby ensuring consistency between the forwarding and control planes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the control plane does not verify forwarding plane state, then the system operates simpler and faster, but the control plane becomes unaware of forwarding table corruption causing blackholing

Engineering Contradiction:

Improvedetection of forwarding plane failuresVSAvoidverification mechanism complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent implements feedback by having the control plane send verification requests (LSP Ping) to test forwarding plane state. The control plane receives status information about forwarding table correctness and uses this feedback to determine whether to consider a backup tunnel operational, thus resolving the contradiction by enabling reliable detection without requiring continuous complex verification of all forwarding states.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system performs self-verification where the control plane actively tests its own forwarding plane state using LSP Ping mechanisms. This self-service approach allows the control plane to detect forwarding table corruption independently without requiring external monitoring systems, improving reliability while maintaining manageable complexity through automated self-testing.

Inventive Principle:

Principle #25Self-service

2Reliability

If backup tunnels are configured without forwarding plane verification, then setup is faster and simpler, but backup tunnels may be corrupted without detection leading to ineffective protection

Engineering Contradiction:

Improvebackup tunnel protection effectivenessVSAvoidverification time before failure detection

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent applies preliminary action by having the control plane verify backup tunnel forwarding state before actual failures occur. The control plane sends verification requests to test backup tunnels proactively, so that when failures happen, the control plane already knows whether backup tunnels are operational. This prevents the loss of time associated with post-failure detection and enables effective backup protection.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The control plane uses feedback from verification requests to determine backup tunnel status. By continuously or periodically checking backup tunnel forwarding state and receiving status information, the control plane can make informed decisions about whether backup protection is available, improving reliability while the feedback mechanism itself manages the time overhead through efficient verification protocols.

Inventive Principle:

Principle #23Feedback

3Reliability

If the control plane assumes backup tunnels are operational based on control plane state alone, then operation is simpler, but corrupted forwarding tables in backup tunnels go undetected

Engineering Contradiction:

Improvesynchronization between control and forwarding planesVSAvoiddetection of forwarding table corruption

Core Design Contradiction:

ReliabilityVSDifficulty of detecting and measuring

Solution Approach 1:

The control plane sends verification requests to forwarding nodes and receives feedback about forwarding table state. This feedback mechanism directly addresses the detection difficulty by providing explicit information about whether forwarding tables are corrupted, enabling the control plane to synchronize its view with actual forwarding plane state without complex measurement systems.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent replaces complex mechanical verification systems with protocol-based verification using LSP Ping and status information exchange. Instead of implementing complex monitoring infrastructure, the system uses existing MPLS control plane protocols to substitute for detection mechanisms, simplifying the approach while enabling reliable detection of forwarding plane corruption.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS7746793B2Consistency between MPLS forwarding and control planes

Publication Date: 2010.06.29 CISCO TECHNOLOGY INC

AI summary

Systems and methods for assuring consistency between MPLS forwarding and control planes. The control plane can be made aware of forwarding plane anomalies and can respond appropriately. One particular application is assuring consistency between forwarding and control planes of a Fast Reroute backup tunnels used to protect an MPLS Traffic Engineering LSP from a link and/or a node failure. When a backup tunnel forwarding failure is detected, the control plane can react by, for example, rerouting the backup tunnel and/or sending a notification to the operator or head-end of the protected Traffic Engineering LSP.