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, preventing the establishment of backup paths and causing traffic loss during network failures.
Innovation Solution
Modifying mLDP control messages to include the address of a remote loop-free alternate (RLFA) node in the LSPRoot field and the ingress router's address in an opaque data field, allowing the RLFA node to correctly establish a backup path without looping, by replacing the LSP Root value with the PQ node address and including the ingress router's address in the opaque data field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mLDP is used to signal the RLFA backup path with the ingress router address in the root node field, then the backup path should be established, but multicast join looping occurs and the backup path cannot be established
Solution Approach 1:
The patent introduces an intermediary mechanism by modifying the mLDP join message to include both the RLFA node address (as the root node for loop avoidance) and the actual ingress router address (in the opaque data field for correct path establishment). This dual-address approach acts as a mediator that resolves the conflict between preventing loops and establishing the correct backup path.
Solution Approach 2:
The patent segments the address information into two distinct parts: the root node address field contains the RLFA node address to prevent loops, while the opaque data field contains the actual ingress router address. This segmentation allows each field to serve its specific function without causing multicast join looping.
2Object-generated harmful factors
If the RLFA node address is placed in the root node field of the mLDP control message, then multicast join looping is avoided, but the backup path may not be correctly established to the ingress router
Solution Approach 1:
The opaque data field serves as an intermediary carrier that transports the actual ingress router address information. This allows the root node field to contain the RLFA address for loop prevention while the opaque field ensures the correct ingress router is identified for proper backup path establishment.
Solution Approach 2:
The patent embeds the ingress router address within the opaque data field, which is nested inside the mLDP control message structure. This nested approach allows additional information to be carried within the existing message framework without disrupting the standard protocol structure.
3Adaptability or versatility
If standard mLDP control messages are used without modification, then protocol compatibility is maintained, but RLFA backup paths cannot be established due to multicast join looping
Solution Approach 1:
The patent makes the opaque data field, which is already part of the standard mLDP message structure, serve a dual function: carrying its original information and also carrying the ingress router address for RLFA backup path establishment. This multi-functionality approach adds RLFA support without requiring fundamental protocol changes.
Solution Approach 2:
The patent changes the parameter content of existing mLDP message fields rather than introducing entirely new fields. By modifying what information is placed in the root node field and opaque data field, the protocol gains RLFA capability while maintaining structural compatibility.
Data Source
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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.