VPLS Provider Edge Loop Prevention via Spanning Tree Segmentation
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Solution Overview
Problem
Existing Ethernet-based Layer2 Virtual Private Network (L2VPN) technologies face challenges in preventing loops caused by Media Access Control (MAC) forwarding, particularly in backbone networks with full mesh connections of Pseudo Wires (PWs), which complicates network management and scalability.
Innovation Solution
The implementation of a method where each Provider Edge (PE) in a VPLS network configures and shares topology information via Generic Associated Channel (G-Ach) to calculate unicast and broadcast minimal spanning trees, allowing for efficient MAC table generation and packet forwarding without establishing a full mesh connection among Network PEs, thereby reducing complexity and enabling flexible network topology and traffic load sharing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If full mesh connection of Pseudo wires (PWs) is established among all Provider Edges (PEs) to prevent MAC forwarding loops, then loop prevention is achieved, but network complexity and management difficulty increase significantly
Solution Approach 1:
The patent segments the network into hierarchical levels with backbone PEs and access PEs having different roles and capabilities. Backbone PEs perform complex spanning tree calculations and topology management, while access PEs have simplified functions. This segmentation allows loop prevention without requiring every PE to participate in full mesh connections and complex protocols.
Solution Approach 2:
The patent introduces a spanning tree protocol as an intermediary mechanism that runs between backbone PEs to establish a logical tree topology. This intermediary layer prevents loops by blocking redundant paths at the backbone level, while allowing access PEs to maintain simpler connections to their respective backbone PEs, thus preventing loops without full mesh complexity.
2Reliability
If full mesh connection of PWs is established among all PEs to ensure reliable MAC forwarding, then loop prevention is achieved, but scalability deteriorates due to rapid expansion of connection scale
Solution Approach 1:
The network is segmented into backbone PEs that handle inter-domain traffic and access PEs that serve customer edges. This hierarchical segmentation allows new access PEs to be added without requiring full mesh connections to all existing PEs, improving scalability while maintaining reliable MAC forwarding through the backbone spanning tree structure.
Solution Approach 2:
The patent transitions from a flat full-mesh topology to a hierarchical topology with multiple dimensions - backbone PEs form a logical tree structure while access PEs connect to specific backbone PEs. This dimensional change from 2D mesh to 3D hierarchical structure enables scalable growth without quadratic increase in connections.
3Adaptability or versatility
If Hierarchy of VPLS (H-VPLS) is used to prevent rapid expansion of full mesh connection scale, then scalability is improved, but network topology flexibility is reduced
Solution Approach 1:
The patent implements dynamic spanning tree protocols that automatically adapt to topology changes in the backbone network. When links or PEs are added or removed, the spanning tree algorithm dynamically recalculates paths and updates forwarding tables, providing topology flexibility without manual reconfiguration while maintaining the hierarchical structure for scalability.
4Reliability
If full mesh connection of PWs is established among all PEs to prevent MAC loops, then loop prevention is achieved, but traffic forwarding complexity increases
Solution Approach 1:
The patent segments forwarding decisions into two levels: backbone PEs perform spanning tree-based loop prevention and path selection for inter-domain traffic, while access PEs perform simpler MAC table lookups for customer traffic. This segmentation improves forwarding efficiency by concentrating complex routing logic at the backbone level while keeping access PE operations simple and fast.
Solution Approach 2:
The spanning tree protocol performs preliminary path calculation and blockage decisions at the backbone level before traffic arrives. Forwarding tables are pre-computed based on the spanning tree topology, so when traffic flows through the network, PEs can make fast forwarding decisions without real-time loop prevention calculations, improving forwarding efficiency while maintaining loop prevention.
Data Source
AI summary
In a VPLS network, a first PE in a VPN instance sends topology information and a bridging MAC address of the first PE to another PE in the VPN instance, receives and stores topology information and bridging MAC addresses from the another PE. The first PE further generates a CE MAC table in the VPN instance according to the stored topology information and bridging MAC addresses of the another PE; calculates a unicast minimal spanning tree by taking the first PE as a root, generates a unicast MAC table in the VPN instance according to the unicast minimal spanning tree. Each PE further selects one of the PEs in the VPN instance as a root bridge, calculates a broadcast minimal spanning tree by taking the root bridge as a root, and generates a broadcast MAC table in the VPN instance according to the broadcast minimal spanning tree.