FEC Stack Query Tracing for Unknown Segment Routing Paths
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Solution Overview
Problem
Conventional LSP Ping mechanisms are inadequate for validating end-to-end connectivity in Segment Routing networks, particularly when FEC details are unknown, especially in scenarios involving MPLS tunnels or LSP stitching, as they lack mechanisms to obtain downstream FEC details and control plane information.
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, which are then used to validate connectivity along the path, repeating the process until end-to-end validation is achieved.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional LSP Ping mechanisms are used in Segment Routing networks, then the validation process is simple, but end-to-end connectivity validation fails when FEC details are unknown
Solution Approach 1:
The initiator node performs preliminary actions by sending trace requests with FEC-Query Sub-TLVs before actual connectivity validation. This allows obtaining downstream FEC details and control plane information in advance, enabling reliable validation even when initial FEC details are unknown. The query mechanism is executed beforehand to gather necessary information for subsequent validation steps.
Solution Approach 2:
The FEC-Query Sub-TLV acts as an intermediary mechanism between the initiator node and intermediate nodes. It enables the initiator to request and receive FEC details from nodes along the path without requiring direct knowledge of downstream FEC information. This intermediary structure facilitates information exchange and enables reliable connectivity validation in Segment Routing networks.
2Reliability
If FEC-Query Sub-TLVs are included in trace requests to obtain downstream FEC details, then connectivity validation reliability improves, but the complexity of the trace request structure increases
Solution Approach 1:
The trace request structure is segmented by introducing the FEC-Query Sub-TLV as a distinct, modular component. This segmentation allows the query mechanism to be added without fundamentally restructuring the entire trace request format. The Sub-TLV can be independently processed by intermediate nodes, enabling reliable FEC validation while maintaining a manageable and structured request format through clear modular boundaries.
3Reliability
If multiple trace requests are sent to obtain FEC details and validate connectivity, then validation completeness improves, but the time required for validation increases
Solution Approach 1:
The validation process maintains continuity by chaining trace requests together, where each request builds upon information obtained from previous requests. The initiator node continuously sends trace requests with updated FEC information until end-to-end validation is achieved. This continuous action ensures complete validation while optimizing the process by avoiding redundant queries and maintaining momentum throughout the validation sequence.
Data Source
AI summary
In one embodiment, a method includes generating a first trace request at an initiator node configured for segment routing, the first trace request comprising a query for FEC (Forwarding Equivalence Class) information, transmitting the first trace request on a path comprising at least one node wherein FEC details for the node are unknown by the initiator node, receiving a response to the first trace request comprising the FEC information, transmitting a second trace request with the FEC information, and receiving a response to the second trace request providing FEC validation. An apparatus is also disclosed herein.