The NSX data plane consists of vSphere Distributed Switch (VDS), kernel modules, User World Agents, NSX Edge, and Distributed routing/firewall and bridging modules. Firstly, let's discuss preparing ESXi clusters for NSX.
What is host preparation? All it does is install the kernel modules and builds a management and control plane domain. The kernel modules that we refer to here are as follows:
Distributed routing
Distributed firewall
VXLAN bridging
In a multi-cluster environment, we need to perform this installation per cluster level. Based on the vSphere design, we can always introduce new hosts to the cluster and preparation is automated for newly added hosts, which makes life easier for architects.