mLDP Multicast Fast Re-Route Over Remote Loop-Free Alternate Backup Path

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Solution Overview

Problem

Multicast join looping occurs in remote loop-free alternate (RLFA) scenarios when using Multicast Label Distribution Protocol (mLDP) for fast re-route (MoFRR), preventing the establishment of backup paths and leading to potential traffic loss during network failures.

Innovation Solution

Modifying the mLDP control messages to signal RLFA backup paths by specifying the address of a remote PQ node in the LSPRoot field and including the ingress router's address in an opaque data field, allowing the PQ node to correctly establish the backup path without looping.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If mLDP control messages are used to signal RLFA backup paths, then fast re-route capability is improved, but multicast join looping occurs preventing backup path establishment

Engineering Contradiction:

Improvebackup path establishmentVSAvoidmulticast join looping

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent introduces an intermediary mechanism by modifying the mLDP control message format to include a specific field that identifies the root node of the primary path. This intermediary field acts as a mediator that allows the RLFA backup path to be established without creating multicast join loops, as the modified control message provides explicit routing information that prevents the looping condition while maintaining fast re-route capability.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent applies parameter changes by modifying the mLDP control message structure to include additional fields: one field identifying the root node of the primary path and another field containing the address of the ingress router. These parameter changes enable the system to distinguish between primary and backup paths, allowing the RLFA backup path to be signaled correctly without causing multicast join looping, thus resolving the contradiction between reliability improvement and harmful loop prevention.

Inventive Principle:

Principle #35Parameter changes

2Ease of operation

If the address of the ingress router is specified in the LSPRoot field, then standard mLDP operation is maintained, but the RLFA backup path cannot be established without looping

Engineering Contradiction:

ImprovemLDP signalingVSAvoidbackup path availability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent segments the root node identification function into two separate fields in the mLDP control message: one field for the root node of the primary path and another field for the ingress router address. This segmentation allows the system to maintain standard mLDP operation for the primary path while simultaneously enabling RLFA backup path establishment, resolving the contradiction between ease of operation and backup path availability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent adds another dimension to the mLDP control message by introducing additional fields beyond the standard LSPRoot field. This dimensional expansion allows the message to carry both the primary path root node information and the RLFA backup path information simultaneously, enabling both standard mLDP operation and backup path establishment without conflict.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Reliability

If a RLFA backup path is established to avoid unicast traffic looping, then traffic resilience is improved, but multicast join looping occurs in the backup path

Engineering Contradiction:

Improvetraffic resilienceVSAvoidmulticast join looping

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent introduces an intermediary field in the mLDP control message that carries explicit root node identification information. This intermediary mechanism allows the RLFA backup path to be established with proper routing information that prevents multicast join looping, while maintaining the traffic resilience benefits of having a dedicated backup path. The intermediary field acts as a mediator that reconciles the conflict between backup path establishment and loop prevention.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent modifies the control message parameters by adding fields that provide explicit routing information for the RLFA backup path. These parameter changes enable the backup path to be established without multicast join looping, as the additional fields provide the necessary information to distinguish backup path traffic from primary path traffic, thus maintaining traffic resilience while preventing harmful loops.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS9998361B2MLDP multicast only fast re-route over remote loop-free alternate backup path

Publication Date: 2018.06.12 JUNIPER NETWORKS INC

AI summary

Techniques are described for enhancements to multicast Label Distribution Protocol (mLDP) to support multicast only fast re-route (MoFRR) over a remote loop free alternate (RLFA) backup path. An egress router is configured to generate a modified mLDP control message to signal the RLFA backup path in which an address of a RLFA node is included in an LSPRoot field and an address of an ingress router is included in an opaque data field. In addition, the RLFA node of the RLFA backup path is configured to recognize that it is identified in the LSPRoot field of the modified mLDP control message, and, in response, look up the ingress router identified in the opaque data field of the modified mLDP control message. The RLFA node is further configured to send an mLDP control message that includes the address of the ingress router in the LSPRoot field towards the ingress router.