Layer 3 Routing Loop Prevention in Link Aggregation Groups
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Solution Overview
Problem
Layer 3 routing loops occur in information handling systems when both links in a Link Aggregation Group (LAG) fail, causing traffic to loop between control bridge devices and reducing bandwidth, as existing failover mechanisms do not effectively prevent such loops.
Innovation Solution
An information handling system with a packet processing engine that determines if a packet includes a control bridge device failover identifier and drops it if layer 3 forwarding would result in the packet being sent back to the control bridge device, preventing routing loops by identifying and mitigating scenarios where layer 3 routing would lead to looping behavior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If failover mechanisms are enabled in both control bridge devices, then network reliability is improved through backup path availability, but layer 3 routing loops occur when both links fail simultaneously
Solution Approach 1:
The patent applies preliminary anti-action by implementing a packet processing engine that proactively identifies and drops packets containing control bridge device failover identifiers before they can complete the routing loop. This preemptive measure prevents the harmful routing loop behavior from fully manifesting, resolving the contradiction between maintaining failover reliability and preventing routing loops.
Solution Approach 2:
The patent converts the harmful routing loop into a detectable condition by utilizing the failover identifier already present in packets. Instead of treating the identifier as merely a routing marker, the system leverages it as a detection mechanism to identify potential loops and drop the packets, thereby transforming the potential harm into a protective feature.
2Productivity
If packets are forwarded through backup paths during link failure, then network connectivity is maintained, but bandwidth is reduced due to looping traffic
Solution Approach 1:
The patent extracts and removes packets that would cause routing loops from the network traffic flow. By identifying packets with control bridge device failover identifiers and dropping them before they can loop, the system eliminates the wasteful bandwidth consumption while preserving legitimate backup path traffic that maintains network connectivity.
Solution Approach 2:
The patent changes the handling parameter of packets containing failover identifiers by transitioning them from a forwardable state to a droppable state. This parameter change occurs dynamically based on the packet's content and routing context, allowing the system to maintain connectivity for legitimate traffic while eliminating bandwidth-wasting looping traffic.
Data Source
AI summary
A layer 3 routing loop prevention system includes a port extender coupled to a first and second control bridges by a Link Aggregation Group (LAG). The first and second control bridges are coupled by an interchassis link. When the first control bridge receives a packet and determines that its LAG link to the port extender is unavailable, it provides a control bridge failover identifier in the packet and performs layer 3 forwarding to send the packet to the second control bridge over the interchassis link. When the second control bridge receives the packet though the interchassis link and determines that its LAG link to the port extender is unavailable, that the packet includes the first control bridge failover identifier, and that layer 3 forwarding will result in the packet being sent back to the first control bridge device, the packet is dropped to prevent layer 3 routing loops.