MCPC Port Priority Vector Switch ID for STP Loop Prevention
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Solution Overview
Problem
The Spanning Tree Protocol (STP) often blocks ports used to establish multi-channel trunks in Multi Chassis Port Channel (MCPC) networks, potentially losing the redundancy benefits of MCPC topologies.
Innovation Solution
A modified Multi Chassis Port Channel (MCPC) priority vector is introduced, including a 'Switch ID' field that determines whether a port is used for a multi-chassis trunk, allowing STP operations to avoid blocking MCT ports and maintain redundancy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If STP is applied to MCPC networks using conventional port priority vectors, then loop prevention is achieved, but MCT ports are blocked causing loss of redundancy
Solution Approach 1:
The patent segments the port priority vector into two distinct types: conventional PPV for regular ports and MCPC-PPV for MCT ports. This segmentation allows STP to operate differently on different port types, preventing MCT ports from being blocked while maintaining loop prevention on regular ports. The MCPC-PPV includes additional fields (Switch ID, MCPC Port ID) that enable MCT ports to be identified and protected from blocking.
Solution Approach 2:
The patent applies local quality by making the port priority vector structure dependent on the port's function. MCT ports use MCPC-PPV with specific characteristics (including Switch ID field set to 0x8000) while regular ports use conventional PPV. This localized differentiation ensures that STP operations are optimized for each port type's specific requirements, preserving MCT port redundancy while maintaining overall network loop prevention.
2Reliability
If a modified MCPC priority vector with Switch ID field is used, then MCT port forwarding is preserved, but the data structure complexity increases
Solution Approach 1:
The patent implements dynamics by making the Switch ID field conditional rather than static. The Switch ID field is set to 0x8000 only for MCT ports, while regular ports use their conventional priority vector structure without this field. This dynamic adaptation allows the priority vector structure to flexibly accommodate different port types, preserving MCT port forwarding functionality while minimizing unnecessary complexity for regular ports.
Solution Approach 2:
The Switch ID field acts as an intermediary marker that enables STP to distinguish MCT ports from regular ports. By setting this field to a specific value (0x8000) for MCT ports, the patent creates a clear identification mechanism that allows STP operations to treat MCT ports differently, ensuring they are not blocked while maintaining the ability to prevent loops on regular ports.
Data Source
AI summary
In one embodiment, a technique for routing traffic in networks represented by logical topologies, such as Multi Chassis Port Channel (MCPC) or Multi Chassis Ether Channel (MCEC) topologies, is provided. By modifying a port priority vector (PPV) to include an additional “Switch ID” field that identifies a designated bridge ID or a local switch ID, depending on whether the corresponding port is used as an MCT, a routing protocol designed to avoid loops in routing paths, such as STP, may avoid blocking MCT ports.