Specific VxRail networks must have routing services that are enabled to support connectivity to external services and applications and end users. These networks include the VxRail external management network and any external-facing networks that are configured for VxRail.

A leaf-spine network topology in the most common use case for VxRail clusters. A single VxRail cluster can start on a single pair of switches in a single rack. When workload requirements expand beyond a single rack, expansion racks can be deployed to support the additional VxRail nodes and switches. The switches at the top of those racks (a “leaf” layer) can be connected together using switches at the adjacent upper layer (a “spine” layer).

You can choose a leaf-spine network topology to support the VxRail cluster or clusters in your data center. If you do, consider enabling Layer 3 routing services at either the spine layer or the leaf layer.

Figure 26.    Layer 2 and Layer 3 boundaries at the leaf layer or spine layer

Establishing routing services at the spine layer means that the uplinks on the leaf layer are trunked ports. The uplinks pass through all the required VLANs to the switches at the spine layer. This topology has the advantage of enabling the Layer 2 networks to span across all the switches at the leaf layer. This topology can simplify VxRail clusters that extend beyond one rack. The Layer 2 networks at the leaf layer do not need Layer 3 services to span across multiple racks. A major drawback to this topology is scalability. Ethernet standards enforce a limitation of addressable VLANs to 4094. This limitation can constrain an application if its workload requires a high number of reserved VLANs, or if you plan multiple VxRail clusters.

Enabling routing services at the leaf layer overcomes this VLAN limitation. This option also helps optimize network routing traffic, as it reduces the number of hops to reach routing services. However, this option does require Layer 3 services to be licensed and configured at the leaf layer. In addition, since Layer 2 VxRail networks now terminate at the leaf layer, they cannot span across leaf switches in multiple racks.

Note: VXLAN Tunnel End Point (VTEP) enables extending Layer 2 networks between switches in physical racks over a Layer 3 overlay network. If your network supports VTEP, it can support a multirack VxRail cluster.

Figure 27.    VTEP tunneling between leaf switches across racks