Network Topology Discovery via STP and AFT Analysis
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Solution Overview
Problem
Existing methods for discovering the physical topology of Ethernet networks are inadequate, particularly in low-cost switches and networks where protocols like LLDP are not implemented, and they fail to detect all physical links, including those blocked by Spanning Tree Protocol (STP), and are vendor-dependent.
Innovation Solution
A network management system broadcasts node discovery messages, uses Spanning Tree Protocol (STP) to set up a tree topology, retrieves information from Address Forwarding Tables, assigns ranking values to switches, and detects blocked interfaces by configuring VLANs and monitoring link status changes, allowing for the discovery of all network nodes and links, including those blocked by STP, without requiring specific protocols on network nodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If LLDP protocol is used for topology discovery, then topology discovery capability is improved, but device compatibility deteriorates because LLDP is not available in low-cost Ethernet switches
Solution Approach 1:
The patent uses an intermediary approach by leveraging the existing STP protocol and AFT tables that are universally supported by all switches, rather than relying on LLDP which is not available in low-cost switches. The management node acts as an intermediary that collects AFT information from all switches and reconstructs the physical topology, thereby achieving compatibility across all device types while maintaining topology discovery capability
Solution Approach 2:
The patent substitutes the LLDP-based discovery mechanism with an alternative approach using STP and AFT tables. Instead of using dedicated topology discovery protocols like LLDP, the system replaces it with a method that utilizes the already-deployed STP protocol and its AFT data structures, which are universally present in all Ethernet switches regardless of cost
2Loss of information
If probe packet based approaches are used, then forwarding topology can be discovered, but physical topology discovery deteriorates because blocked links cannot be detected
Solution Approach 1:
The patent performs preliminary action by utilizing the AFT tables that are already populated by the STP protocol before topology discovery begins. The AFT tables contain information about all physical links including blocked ones, as they are maintained for potential future use. By extracting and analyzing this pre-existing data, the system can discover the complete physical topology without needing to actively probe blocked links
Solution Approach 2:
The patent uses the STP protocol and AFT tables as an intermediary mechanism to indirectly discover blocked physical links. Instead of directly probing links that may be blocked, the system uses the AFT information maintained by STP as an intermediary data source that reveals the presence of all physical links, including those currently blocked by the spanning tree algorithm
3Measurement precision
If STP monitoring approaches are used, then physical topology can be discovered, but vendor dependency increases making the solution inapplicable to all switches
Solution Approach 1:
The patent achieves universality by using the AFT tables and STP protocol which are standardized and implemented by all Ethernet switch vendors. The approach does not rely on vendor-specific proprietary extensions or assumptions about switch behavior. By focusing on the core standardized functionality of STP and AFT that exists in all switches, the solution becomes universally applicable across different vendors and product lines
4Loss of information
If AFT information is collected via SNMP MIBs, then spanning tree paths can be retrieved, but complete physical topology discovery deteriorates because only spanning tree paths are found not redundant paths
Solution Approach 1:
The patent adds another dimension to the analysis by examining multiple switches' AFT tables from different perspectives. Each switch's AFT provides a different view of the network topology. By collecting and correlating AFT information from multiple switches, the system can reconstruct not only the spanning tree paths but also the blocked redundant paths, thereby achieving complete physical topology discovery
Data Source
AI summary
A method and arrangement for discovering the physical topology of a telecommunication network having switches, routers, and a management node interconnected by links in a spanning tree and links to blocked interfaces. The management node broadcasts a ping message and adds replying nodes to the topology. The management node discovers the spanning tree by retrieving address forwarding tables from the switches, assigning them a ranking value, and connecting from the highest ranked nodes to successively lower ranked nodes. The management node discovers the blocked interfaces by configuring a VLAN to include the spanning tree and disabling the spanning tree protocol. The blocked interfaces are turned on and off while matching link down traps are noted and the corresponding links are discovered. Only basic management features of the switches are needed, and all nodes and links are discovered.