Target FEC Stack Queries for Segment Routing Tunnel Validation
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Solution Overview
Problem
Conventional mechanisms for connectivity verification in Segment Routing networks, such as LSP Ping, fail to provide sufficient FEC validation when FECs traverse MPLS tunnels or undergo LSP stitching, as they lack downstream FEC details and cannot instruct downstream FEC details in the label stack.
Innovation Solution
A new semantic for the Target FEC Stack (TFS) is introduced, allowing for a query-based approach where an initiator node includes FEC-Query Sub-TLVs in the trace request to obtain FEC details from adjacent nodes, enabling end-to-end connectivity verification by iteratively replacing FEC-Query Sub-TLVs with received FEC information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional LSP Ping mechanisms are used for connectivity verification, then basic connectivity testing can be performed, but sufficient FEC validation cannot be achieved when FECs traverse MPLS tunnels or undergo LSP stitching
Solution Approach 1:
The patent segments the FEC validation process into multiple stages by introducing FEC-Query Sub-TLVs that can be independently processed at different hops. Each segment of the path can provide its own FEC details, allowing the validation to proceed hop-by-hop through MPLS tunnels and LSP stitching points without requiring end-to-end visibility.
Solution Approach 2:
The patent introduces an intermediary query mechanism (FEC-Query Sub-TLV) that acts as a mediator between the initiator and downstream nodes. This intermediary allows the initiator to request FEC details from adjacent nodes along the path, enabling validation in scenarios where direct downstream FEC details are not available to the initiator.
2Measurement precision
If the initiator node attempts to validate downstream FEC details without query capability, then validation can be performed for known FECs, but validation fails for FECs traversing tunnels where details are unknown
Solution Approach 1:
The patent enables downstream nodes to self-service by providing their own FEC details in response to queries. Each node along the path can independently provide its FEC information when queried, eliminating the need for the initiator to have prior knowledge of downstream FEC details and reducing operational complexity.
Solution Approach 2:
The patent performs preliminary actions by having nodes prepare and cache their FEC details in advance. When a query is received, the node can immediately provide its pre-prepared FEC information, enabling rapid validation without requiring real-time computation or complex lookups during the validation process.
3Reliability
If iterative query and replacement of FEC-Query Sub-TLVs is implemented, then end-to-end connectivity verification can be achieved, but additional message exchanges increase validation time
Solution Approach 1:
The patent maintains continuity of useful action by allowing parallel query operations to proceed along different segments of the path simultaneously. Rather than waiting for sequential responses, multiple FEC queries can be issued in parallel to different hops, and the validation process continues uninterrupted as responses are received, reducing overall validation time.
Data Source
AI summary
In one embodiment, a method includes generating a trace request at an initiator node configured for segment routing, the trace request comprising an FEC (Forwarding Equivalence Class) query corresponding to a label in an FEC stack with an unknown FEC, transmitting the trace request on a path with the unknown FEC, and receiving a response to the trace request, the response comprising FEC information including an identifier associated with a label and a forwarding path and representing a class or category of packets. An apparatus is also disclosed herein.