Both VxRail and a switch fabric based on SFS are architected to expand past the capacity of a single rack. VxRail supports up to 64 nodes in a single cluster and can support the expansion of a single cluster across as many as six physical racks. A switch fabric based on SFS can support a single managed fabric consisting of up to twenty switches in eight racks.
By default, all VxRail networks are configured as Layer 2. To expand a VxRail cluster past a single rack, Layer 3 services are required in the expanded network to enable node discovery and cluster connectivity. In a standard network infrastructure, this means enabling routing for the required VxRail networks between the racks. When using a switch infrastructure with the VxRail personality profile enabled for SFS, the set of tasks required to connect the VxRail networks across racks is automated.
Figure 6. VxLAN network with SFS
SFS supports the automatic creation and expansion of a VxLAN tunnel network across the switch fabric in multiple racks. Virtual Extensible Local Area Network (VxLAN) is an overlay technology that allows you to extend a Layer 2 “overlay” network over a Layer 3 “underlay” network by adding a VxLAN header to the original Ethernet frame and encapsulating it. Encapsulation occurs by adding a VxLAN header on the original Layer 2 Ethernet frame, and placing it into an IP/UDP packet to be transported across the Layer 3 underlay network.
Figure 7. VxLAN packet format
The function of VxLAN is similar to VLAN regarding segmentation, but overcomes the 4096 VLAN limitation, and allows for up to 16 million VxLANs to be created. This key enabler for a multi-rack environment, as well as the transport ability, is why VxRail networks created in a SmartFabric-enabled network are configured as virtual networks, rather than VLANs. While a VLAN has limited mobility within the constraints of a Layer 2 network, a virtual network is configured automatically for transport on the VxLAN-based network, and can therefore enable connectivity across racks.
When a switched fabric is formed using SmartFabric personality profile supported for VxRail, two virtual networks are created: the client management network and the client control network. The client control network is used as the foundation for the VxRail internal management network, whose purpose is node discovery. This allows node discovery for cluster creation and expansion purposes to occur across racks without any additional intervention.
Powered-on VxRail nodes discover each other on the client control network after SFS are enabled and the switch fabric is formed. One VxRail node is elected as the master, and VxRail Manager is started on that master node. The client management network is then used to perform initial connectivity through a configured jump port to VxRail Manager for the purpose of discovering the switch fabric and building the cluster from the discovered nodes.
Figure 8. VxRail networks transport over the VxLAN tunnel
The cluster build process configures the required VxRail networks on the SmartFabric-enabled network. SmartFabric captures those VxRail networks and automatically configure those as virtual networks for transport on the VxLAN tunnel network. The leaf switches in the switch fabric depend on the spine switches on the upper tier for transport on the VxLAN tunnel network across multiple racks, as there is no direct connectivity between leaf switches in separate racks.