Logical UNI and NNI Switch Segmentation for SMLT SPB Clusters
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Solution Overview
Problem
Implementing a switch cluster to interface with both Split Multi-Link Trunk (SMLT) and IEEE 802.1aq networks is challenging, particularly in handling layer 2 broadcast and unicast traffic, as it requires special design considerations to avoid service interruptions and prevent routing loops, especially when transitioning to Shortest Path Bridging (SPB).
Innovation Solution
Each switch in the cluster is implemented as two logical switches—a logical UNI switch and a logical NNI switch, with the logical UNI switch handling forwarding to UNI receivers and the logical NNI switch handling forwarding to NNI receivers, using UNI/NNI and NNI/UNI translations, and treating the Inter-Switch Trunk as two logical channels for efficient packet forwarding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a switch cluster interfaces with both SMLT and IEEE 802.1aq networks, then network connectivity and reliability are improved, but handling layer 2 broadcast and unicast traffic becomes complex and may cause service interruptions or routing loops
Solution Approach 1:
The patent divides each physical switch into two logical switches: a UNI logical switch handling user network interface traffic and an NNI logical switch handling network network interface traffic. This segmentation allows independent handling of broadcast and unicast traffic through dedicated logical channels, simplifying traffic management while maintaining reliability in switch clusters interfacing with both SMLT and IEEE 802.1aq networks
2Reliability
If IST ports are treated as NNI type only, then routing loops are prevented, but service interruptions occur during SPB transition
Solution Approach 1:
The patent implements dynamic port role assignment where IST ports can function as either UNI or NNI type depending on the traffic type and operational context. During SPB transition, ports can dynamically switch roles to maintain service continuity while still preventing routing loops through appropriate logical switching behavior
3Ease of operation
If each physical switch is implemented as two logical switches, then traffic forwarding is simplified and routing loops are prevented, but device configuration and management complexity increases
Solution Approach 1:
The patent introduces logical switches as intermediary entities between physical switch hardware and network traffic. These logical switches abstract the complexity of traffic handling, presenting a simplified forwarding interface to operators while managing the underlying complexity of dual-network interfacing and port role management internally
Data Source
AI summary
Each switch in a switch cluster is implemented as two logical switches—a logical UNI switch and a logical NNI switch implementing a Backbone Edge Bridge (BEB). The logical UNI switch handles forwarding to UNI receivers. The logical NNI switches are treated as independent switches by the SPB control plane and handle forwarding to NNI receivers. The two logical switches exchange packets through UNI/NNI and NNI/UNI translations (Mac-in-MAC encapsulation/decapsulation). The Inter-Switch Trunk is viewed as two logical channels—a UNI logical channel and an NNI logical channel. The logical UNI switch will forward packets having NNI receivers to the logical NNI switch. The logical NNI switch will forward packets having UNI receivers to the logical UNI switch only if the packet has a B-VID matching a B-VID assigned to the node of the switch cluster.