The control plane decouples NSX for vSphere from the physical network and handles the broadcast, unknown unicast, and multicast (BUM) traffic within the logical switches. The control plane is on top of the transport zone and is inherited by all logical switches that are created within it. It is possible to override aspects of the control plane.

The following options are available.

Multicast Mode
The control plane uses multicast IP addresses on the physical network. Use multicast mode only when upgrading from existing VXLAN deployments. In this mode, you must configure PIM/IGMP on the physical network.
Unicast Mode
The control plane is handled by the NSX Controllers and all replication occurs locally on the ESXi host. This mode does not require multicast IP addresses or physical network configuration.
Hybrid Mode
This mode is an optimized version of the unicast mode where local traffic replication for the subnet is offloaded to the physical network. Hybrid mode requires IGMP snooping on the first-hop switch and access to an IGMP querier in each VTEP subnet. Hybrid mode does not require PIM.
Figure 1. Logical Switch Control Plane in Hybrid Mode

Logical Switch Control Plane in Hybrid

This design uses hybrid mode for control plane replication.

Table 1. Design Decisions on the Control Plane Mode of Logical Switches
Decision ID Design Decision Design Justification Design Implications
SDDC-VI-SDN-011 Use hybrid mode for control plane replication. Offloading multicast processing to the physical network reduces pressure on VTEPs as the environment scales out. For large environments, hybrid mode is preferable to unicast mode. Multicast mode is used only when migrating from existing VXLAN solutions. IGMP snooping must be enabled on the ToR physical switch and an IGMP querier must be available.