SR Policy BFD Fault Detection With Reverse Co-Routed Paths
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Solution Overview
Problem
The accuracy of fault detection in segment routing policies using bidirectional forwarding detection (BFD) is compromised due to the non-co-routed transmission paths of BFD packets and response packets, leading to incorrect fault determinations on segment routing policies.
Innovation Solution
Incorporating segment identifier list (SID list) information in BFD packets to enable the receiving end to determine a reversely co-routed forwarding path for sending response packets, ensuring accurate fault detection by aligning the paths of BFD and response packets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the response packet is transmitted in IP routing manner, then the transmission path is determined automatically, but the transmission path may not pass through the network device through which the SR policy passes, leading to non-co-routed transmission
Solution Approach 1:
The patent applies preliminary action by pre-establishing a reverse SR policy that is reversely co-routed with the forward SR policy before BFD detection is performed. The network device stores this pre-configured reverse path information, so when a BFD packet needs to be sent back, the device can immediately use the pre-prepared reverse SR policy without needing to perform complex real-time path calculations or lookups, thus ensuring the response packet follows the same physical path as the original packet while maintaining ease of operation.
2Adaptability or versatility
If the BFD packet and response packet are not co-routed, then the transmission paths are independent, but the fault detection accuracy is reduced due to incorrect fault determination
Solution Approach 1:
The patent applies asymmetry by creating a deliberate asymmetric relationship between the forward and reverse SR policies. While the forward SR policy follows one path from source to destination, the reverse SR policy is specifically configured to follow the same physical path in the opposite direction. This asymmetric configuration ensures that BFD packets and response packets are co-routed through the same network devices, allowing accurate identification of which specific device or link caused a fault, thereby improving fault detection precision while maintaining the flexibility of SR policies.
3Reliability
If a reverse SR policy is established, then the transmission paths are reversely co-routed, but the device complexity increases
Solution Approach 1:
The patent applies feedback by implementing a mechanism where the network device monitors whether BFD response packets are successfully received and sent along the reverse SR policy. This feedback information is used to verify that the reverse co-routing is working correctly and to adjust or re-establish reverse SR policies as needed. The feedback mechanism ensures that the added complexity of managing reverse SR policies translates into reliable co-routed transmission, as the system continuously validates and adjusts the configuration based on actual packet flow observations.
Data Source
AI summary
A fault detection method, a network device, and a system are provided. The method includes: After a first network device receives, through a first forwarding path in an SR policy, a BFD packet that is sent by a second network device and that includes indication information of a SID list, the first network device determines, based on the indication information of the SID list, a second forwarding path that is reversely co-routed with the first forwarding path, and sends a response packet of the BFD packet to the second network device through the second forwarding path, so that the second network device can perform fault detection on the first forwarding path based on the response packet.