Switch Cluster Loop Prevention via LAG ID Tagging
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Solution Overview
Problem
Existing methods for preventing loops in multi-node switch clusters, such as using two Multicast Group IDs per VLAN ID, face limitations in scalability and require complex inter-switch control plane synchronizations during port failures, leading to potential packet loss and loop creation challenges.
Innovation Solution
Assigning a global Link Aggregation Group/Multi-Link Trunk Identifier (LAG/MLT ID) to each LAG/MLT, tagging packets on IST ports with this ID, and using a single Multicast Group Identifier (MGID) per VLAN ID to differentiate packet forwarding, thereby preventing loops and conserving resources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two Multicast Group IDs per VLAN ID are used to prevent loops, then loop prevention is achieved, but the number of MGIDs increases and device complexity increases
Solution Approach 1:
The patent segments the MGID management by creating separate MGID sets for IST ports and user ports. Each set is independently managed, allowing the system to prevent loops without requiring two MGIDs per VLAN. This segmentation reduces the total number of MGIDs needed while maintaining loop prevention capability.
Solution Approach 2:
The patent introduces an intermediary mechanism - the IST port identification and special forwarding rule - that acts as a mediator between packet reception and forwarding decisions. This intermediary layer prevents loops by intercepting packets at the IST port level and applying specific forwarding rules, eliminating the need for multiple MGIDs per VLAN.
2Reliability
If two Multicast Group IDs per VLAN ID are used, then loop prevention is achieved, but scalability is limited due to increased MGID requirements
Solution Approach 1:
By segmenting MGID management into separate sets for IST and user ports, the patent enables the system to scale more efficiently. Each segment is independently managed, allowing the network to accommodate more VLANs and ports without a proportional increase in total MGID consumption, thereby improving scalability.
Solution Approach 2:
The patent makes each MGID multi-functional by designing it to handle both IST port forwarding and user port forwarding within its scope. A single MGID can serve multiple purposes across different port types, reducing the overall number of MGIDs required and enhancing the system's ability to scale.
3Reliability
If inter-switch control plane synchronizations are implemented during port failures, then loop prevention is maintained, but packet loss occurs and operation complexity increases
Solution Approach 1:
The patent implements preliminary action by pre-configuring special forwarding rules for IST ports that automatically prevent loop formation. These rules are established in advance and execute automatically upon packet reception, eliminating the need for real-time control plane synchronizations during port failures and preventing packet loss.
Solution Approach 2:
The forwarding rules enable the system to be self-service during failure scenarios. Each switch independently applies the predefined IST port forwarding rules without requiring coordination or synchronization with other switches, automatically maintaining loop prevention while simplifying operation.
4Productivity
If packets are broadcast to all IST ports, then other nodes receive packet copies for broadcasting, but loop formation risk increases
Solution Approach 1:
The patent applies local quality by implementing different forwarding behaviors for different packet destinations. Packets received on IST ports are subjected to special local processing - they are forwarded to user ports according to specific rules while preventing re-transmission back to IST ports. This localized quality control at the forwarding decision level enables efficient packet distribution while preventing loops.
Solution Approach 2:
The patent uses preliminary action by pre-establishing forwarding rules that differentiate between IST port packets and user port packets. These rules are configured in advance to direct IST port packets to appropriate user ports while blocking any path that would return packets to IST ports, thereby enabling efficient distribution without loop formation risk.
Data Source
AI summary
A LAG/MLT ID is assigned to each LAG/MLT connecting to a switch cluster. Packets transmitted on the IST port are tagged with the LAG/MLT ID. Each switch in the switch cluster maintains a single MGID per VLAN ID. The MGID includes all IST ports as well as VLAN ID user port members. If a broadcast packet is received on an IST, any packet copy destined to the receiving IST port is dropped and any packet copy destined to a LAG/MLT port that matches the incoming tag is dropped. The LAG/MLT ID is preserved when the packet is sent to other IST ports and is removed when the packet is sent to a user port. By using a global ID for the LAG/MLT differentiated treatment of packets forwarded on the IST may be achieved using a single MGID per VLAN ID thus conserving resources.