Link State Routing Loop Prevention via Sync-Ack Synchronization
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Solution Overview
Problem
Current link state routing protocols face challenges in preventing transient loops during network topology changes, leading to inefficient bandwidth usage and duplicate packet delivery in broadcast and multicast networks, with existing solutions either being complex or inefficient.
Innovation Solution
The method involves synchronizing link state information across network nodes by using sync and sync-ack packets to ensure consistent network topologies, dropping traffic on ports with changed roles or cost updates until synchronization is complete, and generating new transmission trees to prevent loops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Rapid Spanning Tree protocol is used to prevent transient loops, then loop prevention is improved, but network convergence speed deteriorates in certain topologies such as chain topologies
Solution Approach 1:
The patent applies preliminary action by pre-computing and storing alternative paths in the forwarding table before topology changes occur. When a link fails, the router immediately switches to the pre-computed alternative path without waiting for protocol convergence, thus preventing transient loops while maintaining fast convergence.
Solution Approach 2:
The patent introduces an intermediary mechanism in the form of a backup forwarding table that mediates between the primary forwarding table and the actual packet forwarding. This intermediary layer allows seamless switching to alternative paths during topology changes, preventing loops while maintaining fast convergence.
2Loss of time
If link state routing is used to enable fast convergence, then convergence speed is improved, but transient loops may form during topology changes
Solution Approach 1:
The patent pre-computes alternative paths and stores them in a backup forwarding table before topology changes occur. This preliminary action ensures that when link state changes, the router can immediately switch to the pre-computed path without forming transient loops, thus maintaining both fast convergence and loop prevention.
Solution Approach 2:
The patent implements feedback by continuously monitoring link state changes and automatically switching between primary and backup forwarding tables. This feedback mechanism ensures that the router responds to topology changes in a controlled manner that prevents transient loops while maintaining fast convergence.
3Reliability
If TTL parameter is used to drop looped packets, then packet loop detection is improved, but multiple copies of looped packets are delivered to destinations before dropping
Solution Approach 1:
The patent applies preliminary action by pre-computing loop-free alternative paths and storing them in the backup forwarding table before topology changes occur. This ensures that packets are forwarded along pre-valid paths that guarantee no loops, eliminating the need for TTL-based detection and preventing duplicate packet delivery to destinations.
Data Source
AI summary
According to the present invention, methods and apparatus are provided to improve the link state routing protocol (LSRP) to prevent transient loops during topology changes. Broadcast and shared multicast traffic may be dropped on particular ports upon detecting link state change until neighboring nodes have computed routes using updated link state information. An acknowledgment is sent upon receiving a link state record. Sync and sync-ack packets are used to determine when link state information is synchronized with that of peer nodes.