Target FEC Stack Queries for Segment Routing Path Validation
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Solution Overview
Problem
Conventional mechanisms for connectivity verification in Segment Routing networks, such as LSP Ping, are insufficient for validating Forwarding Equivalence Class (FEC) details when packets traverse multiple MPLS tunnels or undergo LSP stitching, as they lack the ability to obtain downstream FEC details, leading to incomplete path validation.
Innovation Solution
A new semantic for the Target FEC Stack (TFS) is introduced, allowing an initiator node to query adjacent nodes for control plane details of downstream nodes by including FEC-Query Sub-TLVs in trace requests, which are then replaced with received FEC information to continue the connectivity verification process along the path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional LSP Ping mechanisms are used for connectivity verification in Segment Routing networks, then the verification process is simple, but the ability to validate FEC details is insufficient when packets traverse multiple MPLS tunnels or undergo LSP stitching
Solution Approach 1:
The connectivity verification process is segmented into multiple iterative steps: initial trace request with FEC-Query Sub-TLV, receiving FEC information from adjacent nodes, replacing FEC-Query with received FEC details, and continuing verification. This segmentation allows comprehensive FEC validation across multiple MPLS tunnels while maintaining manageable process complexity through structured iteration.
Solution Approach 2:
The initiator node performs preliminary actions by including FEC-Query Sub-TLVs in the initial trace request before actual FEC validation can occur. This preliminary query mechanism retrieves necessary FEC details from adjacent nodes in advance, enabling subsequent comprehensive path validation without requiring the initiator to have complete FEC information beforehand.
2Loss of information
If the initiator node includes FEC-Query Sub-TLVs in trace requests to obtain downstream FEC details, then comprehensive path validation is achieved, but the complexity of the verification process increases due to iterative queries and replacements
Solution Approach 1:
The verification process maintains continuity by iteratively replacing FEC-Query Sub-TLVs with received FEC information and immediately continuing the trace request without interruption. This continuous action ensures that FEC details are obtained and validated along the entire path without breaking the verification flow, minimizing idle time while comprehensively gathering FEC information.
Solution Approach 2:
Adjacent nodes provide feedback by responding to FEC-Query Sub-TLVs with actual FEC details. This feedback mechanism enables the initiator node to obtain missing FEC information from downstream nodes, replace the queries with received details, and continue verification. The feedback loop ensures complete FEC information collection while maintaining efficient iterative processing.
3Reliability
If iterative FEC query and replacement is performed along the path, then end-to-end connectivity verification is enabled, but the number of processing steps increases
Solution Approach 1:
The verification process is made dynamic through adaptive iteration: the initiator node dynamically adjusts the trace request by replacing FEC-Query Sub-TLVs with received FEC information only when needed, rather than performing fixed sequential steps. This dynamic approach maintains high reliability by obtaining necessary FEC details while improving productivity by avoiding unnecessary processing steps when FEC information is already available.
Data Source
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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.