SPB Loop Mitigation via Alternate Ingress Check
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Solution Overview
Problem
In Ethernet networks implementing the shortest path bridging (SPB) protocol, existing loop mitigation methods, such as reverse path forwarding check (RPFC), restrict resilience options and delay traffic rerouting, leading to potential network meltdowns, especially in multicast frame forwarding scenarios.
Innovation Solution
A method and system that utilize a filtering database (FDB) for guiding Ethernet frame forwarding, with coordinated updates through digest exchanges between nodes, and an alternate ingress check process that allows for loop-free alternate paths selection, enabling faster switching to alternate paths during network failures without strict RPFC enforcement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If reverse path forwarding check (RPFC) is strictly enforced to prevent forwarding loops, then loop mitigation is improved, but network resilience deteriorates due to restricted rerouting options and delayed traffic switching
Solution Approach 1:
The patent applies different ingress check strictness levels to different network conditions and frame types. For unicast frames, a relaxed check allows rerouting to alternate ports when the shortest path is unavailable. For multicast frames, strict RPFC enforcement prevents loops. This local differentiation resolves the contradiction by allowing resilience where safe and maintaining loop prevention where critical.
Solution Approach 2:
The patent dynamically adjusts ingress check behavior based on real-time network state. When a port failure is detected, the system transitions from strict RPFC enforcement to relaxed checking that permits alternate path usage. This dynamic adaptation allows the system to maintain loop mitigation under normal conditions while enabling resilient rerouting when failures occur.
2Reliability
If strict reverse path forwarding check is applied to all frames, then forwarding loop prevention is improved, but traffic rerouting speed deteriorates due to delayed switching decisions
Solution Approach 1:
The patent performs preliminary classification of frames as unicast or multicast before applying ingress checks. This preliminary action allows the system to apply appropriate check strictness levels immediately, avoiding the time penalty of strict checking for unicast frames that can safely use relaxed checks during rerouting scenarios.
Solution Approach 2:
The patent changes the ingress check parameter (strictness level) based on frame type and network conditions. For unicast frames during failure scenarios, the parameter is changed from strict to relaxed, enabling faster rerouting decisions without compromising loop prevention through the underlying SPB protocol mechanisms.
3Productivity
If relaxed loop mitigation is used to enable faster rerouting, then network resilience is improved, but the risk of forwarding loops increases
Solution Approach 1:
The patent applies relaxed loop mitigation only to unicast frames where distance inversion loops are less critical, while maintaining strict RPFC enforcement for multicast frames where loops would be catastrophic. This local quality differentiation allows resilience improvement without accepting unacceptable loop risks in critical scenarios.
Solution Approach 2:
The patent uses the SPB protocol's inherent mechanisms (shortest path tree calculations, port role assignments) as an intermediary layer that provides loop prevention guarantees even when relaxed ingress checking is applied. This intermediary ensures that relaxed mitigation does not actually increase loop risk while enabling faster rerouting.
Data Source
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AI summary
A method forward Ethernet frames at a node in a network supporting an implementation of shortest path bridging (SPB) protocol is disclosed. The method starts with a shortest path computation for the node (referred to as the computing node). The shortest path computation selects at least a shortest path to each destination node in the network, where a neighboring node on the shortest path to reach each node is recorded. Then it computes a downstream loop-free alternate (LFA) node for a destination node, where the LFA node is downstream of the computing node but not on the selected shortest path to the destination node from the computing node. Then when connectivity to the neighboring node on the computed shortest path is detected to be abnormal, the node forwards an Ethernet frame with a destination media access control (MAC) address corresponding to the destination node through the LFA node.