This section provides best practices for Layer 2 access network design. Although many network architectures might meet enterprise requirements, this document takes a closer look at what is commonly referred to as the Triangle Looped Access Topology, which is the most widely implemented architecture in enterprise data centers.

Figure 2.   Triangle Looped Access Topology

The Looped Design Model extends VLANs between the aggregation switches, thus creating the looped topology. To prevent loops, Spanning Tree is implemented, using Rapid PVST+ or MST. For each path, a redundant path also exists, which is blocking until the primary path is not available. Access layer uplinks may be used to load balance VLANs. A key point to consider with the Looped Access Topology is the utilization of the inter-switch link between the distribution switches. The utilization must be monitored closely because this link is used to reach active services.

The Looped Triangle Access Topology supports VLAN extension and L2 adjacency across the Access layer. By using STP and dual homing, the Looped Triangle is resilient. Stateful services are supported at the aggregation layer and quick convergence with 802.1W/S.

Using the Triangle Looped Topology allows for multiple access switches to interface with the external network of the PowerScale scale-out NAS environment. Each PowerScale node within a cluster is part of a distributed architecture, which allows each node to have similar properties regarding data availability and management.