Multicast LDP Label Distribution Loop Prevention
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Solution Overview
Problem
In multicast networks, transient micro loops occur due to network changes and inconsistencies between control and data planes, leading to potential exponential-traffic loops and convergence issues, especially when nodes converge at different times, causing traffic to loop back and forth between nodes.
Innovation Solution
A method is introduced to prevent transient micro loops by immediately cleaning up local rewrites and sending label withdrawal and release messages upon nexthop changes, setting multicast LDP label hold time to zero, and ensuring ordered label distribution and rewrite installation using strict path vector-based procedures, making new labels disjoint from old ones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If nodes converge at different times during network changes, then network flexibility and adaptability are improved, but transient micro loops and traffic looping occur between nodes
Solution Approach 1:
The patent applies preliminary action by requiring nodes to perform convergence detection and send confirmation messages before activating new label mappings. This ensures that all nodes are synchronized and ready before traffic is redirected, preventing transient micro loops while maintaining convergence flexibility. The path vector verification and confirmation message exchange are performed in advance of the actual traffic switching.
2Reliability
If label hold time is extended to ensure proper label distribution, then label distribution reliability is improved, but convergence time and network stabilization duration increase
Solution Approach 1:
The patent implements feedback mechanisms where nodes send confirmation messages to verify that labels have been properly received and installed before considering the label distribution complete. This feedback loop ensures reliability by confirming successful label installation while reducing convergence time by immediately proceeding to the next step once confirmation is received, rather than waiting for extended hold periods.
Solution Approach 2:
The patent dynamically adjusts the label hold time parameter based on network conditions and convergence status. Instead of using a fixed extended hold time, the system monitors convergence progress and releases labels promptly once convergence is detected through path vector verification and confirmation messages, thereby reducing unnecessary waiting time while maintaining reliability.
3Productivity
If path vectors are not strictly verified during label distribution, then label distribution speed is improved, but loop detection capability and network stability deteriorate
Solution Approach 1:
The patent performs path vector verification as a preliminary check before installing label mappings. Nodes verify that the received path vector is consistent with their own routing information and that no loops exist in the proposed path. This preliminary verification ensures loop detection capability is maintained while allowing rapid label distribution to proceed once verification is complete.
Data Source
AI summary
A method of distributing labels in a label distribution protocol multicast network having a root node and at least one leaf node comprises the steps, performed at a receiving node, of receiving a label and path vector from a distributing node, carrying out loop or convergence detection from the received path vector and, if convergence or no loop is detected, sending a receiving node label and path vector to its nexthop node in the network.