Bidirectional BFD via Segment Routing Tunnels
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Solution Overview
Problem
Conventional Seamless Bidirectional Forwarding Detection (S-BFD) protocols face vulnerabilities due to unreliable return paths, leading to unnecessary path failure declarations, as they rely on best-effort IP routing for the return path, which can suffer from latency and other issues.
Innovation Solution
The implementation of Segment-Routing Traffic-Engineering (SR-TE) forward and reverse paths using Multiprotocol Label Switching (MPLS) protocols, where a Binding SID (B-SID) is used to propagate the return packet along a traffic-engineered SR-TE path, eliminating the need for a BFD reflector and ensuring the packet is not dropped by the source node.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional S-BFD protocol is used with best-effort IP routing for return path, then implementation simplicity is maintained, but reliability deteriorates due to vulnerable return paths and unnecessary path failure declarations
Solution Approach 1:
The routing path is segmented into forward path (source to destination) and reverse path (destination to source), with each path independently configured and optimized. The forward path uses SR-TE tunneling for reliability, while the reverse path uses best-effort IP routing for simplicity, resolving the contradiction by applying different strategies to different segments.
Solution Approach 2:
Different routing strategies are applied to different directions: the forward path employs traffic-engineered SR-TE routing with explicit path control for high reliability, while the reverse path uses conventional best-effort IP routing for simplicity. This local differentiation allows each path to be optimized for its specific requirements.
2Reliability
If traffic-engineered SR-TE path is used for forward path, then continuity monitoring reliability is improved, but return path vulnerability increases due to lack of symmetric engineering
Solution Approach 1:
Instead of only engineering the forward path and relying on best-effort for return, the invention inverts the approach by also engineering the reverse path using SR-TE tunneling. This symmetric treatment ensures both forward and return paths benefit from traffic engineering, eliminating the vulnerability imbalance.
Solution Approach 2:
The reverse SR-TE tunnel is pre-configured before continuity checks are performed. This preliminary setup ensures that when continuity monitoring is needed, the return path is already optimized and ready, avoiding the need for post-hoc path engineering and ensuring consistent reliability.
3Adaptability or versatility
If BFD reflector is used at destination node, then bidirectional detection capability is provided, but device complexity and potential packet dropping increase
Solution Approach 1:
The BFD reflector function is extracted and removed from the destination node. Instead of having the destination node actively participate in BFD by receiving and reflecting packets, the invention uses unidirectional detection where the source node sends packets and interprets their return as confirmation of path availability, eliminating the need for complex reflector configuration.
Solution Approach 2:
The source node performs self-detection by sending BFD packets and interpreting the return traffic as confirmation of its own path status. This self-service approach eliminates the need for the destination node to actively manage BFD sessions, reducing overall system complexity while maintaining detection capability.
Data Source
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AI summary
Systems and methods for monitoring the continuity between endpoints in a network are provided. A method (120), according to one implementation, includes entering (122) a first list of one or more Segment Identifiers (SIDs) into a Bidirectional Forwarding Detection (BFD) request packet, the first list of one or more SIDs defining a Segment-Routing Traffic-Engineering (SR-TE) forward path from a source node to a destination node. The method (120) also includes entering (124) a second list of one or more SIDs into the BFD request packet, the second list of one or more SIDs defining an SR-TE reverse path back from the destination node that eliminates involvement of a BFD reflector of the destination node. Also, the method (120) includes entering (126) a revised-BFD request into the BFD request packet, the revised-BFD request having a Your Discriminator field set to a discriminator value associated with the source node.