LSP Ping Traceroute with Entropy Labels for ECMP Path Validation
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Solution Overview
Problem
MPLS networks face challenges in performing effective LSP connectivity tests due to incompatible load balancing algorithms used by transit LSRs, leading to incomplete multipath information and inability to trace and validate all ECMP paths, especially when some LSRs implement IP-based load balancing while others use label-based load balancing.
Innovation Solution
Introduction of a new multipath information type 10 and new DS flags in DSMAP/DDMAP messages to query and return both IP and label multipath information, along with associated entropy labels, allowing LSP ping and traceroute to trace and validate ECMP paths even in networks with entropy labels and mixed load balancing algorithms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional LSP ping/trace is used in MPLS networks with mixed load balancing algorithms, then connectivity tests can be performed in networks without entropy labels, but the tests fail to trace and validate all ECMP paths when entropy labels are present and LSRs use incompatible load balancing algorithms
Solution Approach 1:
The patent changes the parameters used for load balancing by introducing entropy labels that can be independently manipulated. Instead of relying on IP header fields or label stack parameters that conflict with existing LSR load balancing algorithms, the entropy label provides a new parameter space that can be modified without affecting the forwarding plane's load balancing decisions. This allows test packets to be distributed across all ECMP paths reliably.
Solution Approach 2:
The entropy label acts as an intermediary between the LSP ping/trace functionality and the MPLS forwarding plane. By embedding test packet identifiers in the entropy label rather than in IP headers or other forwarding-relevant fields, the patent creates a mediation layer that allows connectivity testing without interfering with or being interfered by the load balancing algorithms of transit LSRs.
2Loss of information
If LSP ping/trace uses existing multipath information types, then the protocol structure remains simple, but it cannot retrieve complete multipath information when LSRs impose entropy labels and use label-based or IP-based load balancing
Solution Approach 1:
The patent adds another dimension to the multipath information retrieval by introducing a new multipath information type (type 10) that operates in a different parameter space than existing types. Instead of trying to extend existing multipath types that work with IP addresses or labels, the new type queries LSRs for entropy label assignments, creating a parallel information retrieval dimension that complements rather than conflicts with existing mechanisms.
Solution Approach 2:
The patent segments the multipath information retrieval process into distinct types: existing types (0-9) for traditional IP/label-based multipath information, and new type 10 for entropy label-based multipath information. This segmentation allows the protocol to handle different information types independently, maintaining simplicity for traditional cases while enabling complete multipath tracing in entropy label networks.
3Productivity
If LSRs use label-based load balancing with entropy labels, then load distribution across ECMP paths is achieved, but LSP ping/trace cannot determine which entropy labels map to which downstream LSRs
Solution Approach 1:
The patent implements a feedback mechanism where LSRs return multipath information type 10 in response to LSP ping/trace queries, providing the mapping between entropy labels and downstream LSRs. This feedback loop allows the initiating LSR to learn which entropy labels correspond to which ECMP paths, enabling both effective load balancing and complete connectivity testing across all paths.
Data Source
AI summary
The present disclosure provides for carrying downstream mapping information in an echo request message and/or echo reply message, which can describe both IP (Internet Protocol) multipath information and label multipath information. A transit node (e.g., an LSR element) that receives an echo request message from an initiator node determines downstream mapping information, which is returned to the initiator node. Transit node determines whether a newly defined type of multipath information (type 10) should be generated to return the downstream mapping information, based on whether transit node performs load balancing based on labels or IP header information, and whether transit node imposes entropy labels. A multipath information type 10 element includes either IP multipath information or label multipath information, as well as associated label multipath information that includes one or more entropy labels that map to the IP or label multipath information being returned.