RSVP Make-Before-Break Label Reuse in MPLS Networks
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Solution Overview
Problem
The existing methods for establishing new Label Switched Paths (LSPs) in MPLS networks during make-before-break procedures require frequent label updates, leading to network churn and potential disruptions, especially when existing and new paths only partially overlap.
Innovation Solution
The technique involves reusing downstream-assigned labels for new LSP instances when the paths overlap, allowing non-ingress routers to avoid updating label routes in their forwarding planes, and enabling ingress routers to skip updating ingress routes in certain cases, thereby reducing network churn and speeding up the establishment of new paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If new LSP instances are established with new labels during make-before-break procedures, then label routing accuracy is maintained, but network churn increases and convergence time is extended
Solution Approach 1:
The system performs preliminary actions by checking path overlap between existing and new LSP instances before label assignment. When overlap is detected, the system proactively reuses existing labels instead of allocating new ones, thereby avoiding unnecessary forwarding plane updates and reducing convergence time while maintaining routing accuracy through controlled label reuse policies
Solution Approach 2:
The system changes the label assignment parameter dynamically based on path overlap conditions. When paths overlap, the system changes from allocating new labels to reusing existing labels, thereby reducing network churn and convergence time. When paths do not overlap, the system maintains the traditional new label allocation to ensure routing accuracy
2Measurement precision
If new labels are allocated for each new LSP instance, then forwarding plane accuracy is maintained, but device complexity and update overhead increase
Solution Approach 1:
The system applies local quality by making label assignment decisions at each downstream router based on local path overlap conditions. Each router independently determines whether to reuse or allocate new labels for its outgoing interfaces, thereby maintaining forwarding accuracy where needed while reducing update overhead where paths overlap, without requiring global label reassignment
3Reliability
If label updates are performed for all new LSP instances, then routing accuracy is ensured, but network stability decreases due to increased churn
Solution Approach 1:
The system performs partial label updates only where necessary - specifically, only when LSP paths do not overlap. When paths overlap, the system intentionally performs no label updates (partial action), thereby maintaining routing accuracy for non-overlapping paths while preserving network stability by avoiding unnecessary updates in overlapping regions, thus reducing overall network churn
Data Source
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AI summary
Techniques are described for establishing a second label switched path (LSP) instance of an LSP having a first LSP instance. In one example, for each downstream router designated for the second LSP instance of the LSP, the router determines whether the router is part of the first instance of the LSP and, if so, whether the first and second LSP instances for that downstream router share a common link to a nexthop router. If the first and second LSP instances share a common link to a nexthop router, the downstream router transmits a first message to the nexthop router, wherein the first message includes a suggested label. The downstream router receives, from the nexthop router, a second message, wherein the second message includes the suggested label. In another example, a label reuse indicator flag in a message from the ingress router causes routers on the second LSP instance to reuse the label of the first LSP instance when the same link is used to the upstream router for both LSP instances.