MPLS LSP Data Plane Failure Detection via Connectivity Requests
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Solution Overview
Problem
Current methods lack a practical and quick solution to detect the liveliness of data plane failures in Label-Switched Paths (LSPs), leading to time-consuming manual processes and potential misrouting of packets due to corrupted forwarding information.
Innovation Solution
The implementation of MPLS connectivity request messages that test packet delivery through the LSP, supporting both basic connectivity checks and fault isolation tests, allowing for periodic verification of LSP connectivity and operation matching between the control and data planes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If manual memory dumps are used to detect LSP failures, then detection capability is provided, but time consumption increases significantly
Solution Approach 1:
The system performs self-diagnosis by having the LSP itself generate and process diagnostic messages. The ingress LSR sends diagnostic messages through the LSP, and intermediate/egress LSRs automatically process and respond to these messages, eliminating the need for manual memory dumps and significantly reducing detection time.
Solution Approach 2:
The system establishes a feedback mechanism where egress LSRs send diagnostic replies back to ingress LSRs through the control plane. This feedback loop enables automatic detection of data plane failures by comparing control plane routing information with actual data plane forwarding behavior.
2Extent of automation
If control plane routing is used to detect data plane failures, then automated detection is achieved, but accuracy decreases due to potential mismatches between control and data planes
Solution Approach 1:
The diagnostic process is segmented into distinct phases: sending diagnostic messages through the data plane, receiving replies through the control plane, and comparing results. This segmentation allows the system to separately test data plane forwarding correctness against control plane routing information, improving detection accuracy while maintaining automation.
Solution Approach 2:
The system uses diagnostic messages as intermediaries to bridge the control plane and data plane. These messages traverse the data plane to test actual forwarding behavior while using the control plane for reliable message delivery and comparison, enabling accurate automated detection of mismatches between the two planes.
Data Source
AI summary
Detecting if a label-switched path (LSP) is functioning properly. To test that packets that belong to a particular Forwarding Equivalence Class (FEC) actually end their MPLS LSP on an label switching router (LSR) that is an egress for that FEC, a request message carrying information about the FEC whose LSP is being verified may be used. The request message may be forwarded like any other packet belonging to that FEC. A basic connectivity test as well as a fault isolation test are supported. In a basic connectivity test mode, the packet should reach the end of the LSP, at which point it is sent to the control plane of the egress LSR. The LSR then verifies that it is indeed an egress for the FEC. In a fault isolation test mode, the packet is sent to the control plane of each transit LSR, which performs various checks that it is indeed a transit LSR for the LSP. The transit LSR may also return further information that helps check the control plane against the data plane, i.e., that forwarding matches what the routing protocols determined as the path. A reliable return path is used for the reply.