VLAN-Specific Topology Change Handling in RSTP Switches

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Solution Overview

Problem

The Rapid Spanning Tree Protocol (RSTP) causes unnecessary flushing of forwarding tables for all VLANs in a network when topology changes occur, leading to increased network traffic and inefficiency, especially in scenarios where Multiple Spanning Tree Protocol (MSTP) is not desirable due to cost or other considerations.

Innovation Solution

Implementing a special topology change packet, such as a modified Ethernet packet, that allows topology changes to be specific to a VLAN or a subset of VLANs, rather than affecting all VLANs, while maintaining a single topology map, by communicating the change through a peer spanning tree instance and only flushing the relevant VLAN's forwarding tables.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the standard RSTP topology change mechanism is used, then topology changes are detected and propagated across the network, but all VLAN forwarding tables are flushed causing unnecessary network traffic and inefficiency

Engineering Contradiction:

Improvetopology change detectionVSAvoidnetwork traffic efficiency

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent segments the topology change notification mechanism by introducing VLAN-specific topology change indicators within the RSTP framework. Instead of flushing all VLAN forwarding tables, the system selectively notifies only the affected VLANs, dividing the monolithic topology change response into granular, VLAN-specific actions.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent applies local quality by making topology change responses specific to the affected VLAN rather than applying a universal flush to all VLANs. The system modifies the RSTP topology change notification to include VLAN identifiers, allowing each switch to selectively update only the forwarding tables relevant to the changed topology.

Inventive Principle:

Principle #3Local quality

2Adaptability or versatility

If Multiple Spanning Tree Protocol (MSTP) is implemented to handle VLAN-specific topology changes, then selective topology change propagation is achieved, but network infrastructure cost increases

Engineering Contradiction:

ImproveVLAN-specific topology controlVSAvoidprotocol implementation complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent introduces dynamic VLAN-specific topology change handling within the static RSTP framework. The system dynamically determines which VLANs are affected by topology changes and selectively propagates notifications only to those VLANs, rather than using a fixed MSTP structure with multiple spanning tree instances.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the parameters of the RSTP topology change notification by incorporating VLAN identifier fields into the topology change messages. This modification allows the protocol to carry VLAN-specific information, enabling selective forwarding table updates without requiring the complex MSTP protocol structure.

Inventive Principle:

Principle #35Parameter changes

3Stability of the object's composition

If forwarding tables are flushed for all VLANs upon topology change, then network topology consistency is maintained, but network performance and efficiency deteriorate

Engineering Contradiction:

Improvetopology consistencyVSAvoidnetwork throughput

Core Design Contradiction:

Stability of the object's compositionVSProductivity

Solution Approach 1:

The patent applies partial action by flushing only the necessary portion of forwarding tables - specifically, only the VLANs affected by the topology change - rather than performing a complete flush of all VLAN forwarding tables. This selective approach maintains topology consistency for affected VLANs while avoiding unnecessary disruptions to other VLANs.

Inventive Principle:

Principle #16Partial or excessive action

Solution Approach 2:

The patent introduces VLAN identifier fields as intermediaries between the topology change detection mechanism and the forwarding table update process. These identifiers act as mediators that connect the physical topology change to the specific logical VLANs affected, enabling precise targeting of forwarding table updates without manual configuration.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS8873431B1Communications system and method for maintaining topology in a VLAN environment

Publication Date: 2014.10.28 ADTRAN INC

AI summary

In accordance with a non-limiting example, a communications system includes a plurality of Virtual Local Area Networks (VLAN) enabled switches interconnected together and each having a plurality of ports and configured into a plurality of VLAN's in a single topology map. The switches each comprise a processor and transceiver and configured to process and transport data packets and further comprising forwarding tables and operating in accordance with a Spanning Tree Protocol in a single topology map, for example, operating with the Rapid Spanning Tree Protocol and not having multiple topologies. When a topology changes occurs to a specified VLAN, the switches are configured to flush the forwarding tables only for the specified VLAN associated with the port of the switch whose state change caused the topology change.