Dell PowerEdge R730xd Deployment Manual

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Dell PowerEdge R730xd Deployment Manual Manual pdf 11 page image

11 Dell EMC Networking with Isilon Front-End Deployment and Best Practices Guide | version 1.04 Leaf-spine overviewThe connections between leaf and spine switches can be layer 2 (switched) or layer 3 (routed). The terms“layer 3 topology” and “layer 2 topology” in this guide refer to these connections. In both topologies,downstream connections to servers, storage and other endpoint devices within the racks are layer 2 andconnections to external networks are layer 3.The following concepts apply to layer 2 and layer 3 leaf-spine topologies:• Each leaf switch connects to every spine switch in the topology.• Servers, storage arrays, edge routers and similar devices always connect to leaf switches, never tospines.The layer 2 and layer 3 topologies each use two leaf switches at the top of each rack configured as a VirtualLink Trunking (VLT) pair. VLT allows all connections to be active while also providing fault tolerance. Asadministrators add racks to the data center, two leaf switches configured for VLT are added to each new rack.The total number of leaf-spine connections is equal to the number of leaf switches multiplied by the number ofspine switches. The bandwidth of the fabric may be increased by adding connections between the leaf andspine layer as long as the spine layer has the capacity for the additional connections.Leaf-Spine architecture4.1 Design considerationsThere are many different options regarding the selection of the correct topology that will best fit the needs ofthe data center. In this section, the different protocols, topologies, and best practices will be covered. Themain differentiation will be whether the L2/L3 boundary is located at the spine layer or at the leaf layer. Whencompared to a layer 3 topology, a layer 2 topology is generally less complex but has some limitations thatmust be considered. These include:• For each VLAN, the layer 2 topology creates one large broadcast domain across the fabric. The layer3 topology has the benefit of containing broadcast domains to each rack.• The layer 2 topology is limited to 4094 VLANs across the fabric. The layer 3 topology allows up to4094 VLANs per rack.• The layer 2 topology is limited to two physical switches at the spine layer (configured as VLT peers).In a layer 3 topology, additional spines may be added as needed to provide additional paths andbandwidth. Therefore, a layer 3 topology is more scalable and is better suited for very large networks.