The control plane decouples NSX-T from the physical network, and handles the broadcast, unknown unicast, and multicast (BUM) traffic in the segments (logical switches).

The following options are available for BUM replication on segments.

Table 1. BUM Replication Mode of NSX-T Segments

BUM Replication Mode


Hierarchical Two-Tier

In this mode, the ESXi host transport nodes are grouped according to their TEP IP subnet. One ESXi host in each subnet is responsible for replication to a ESXi host in another subnet. The receiving ESXi host replicates the traffic to the ESXi hosts in its local subnet.

The source ESXi host transport node knows about the groups based on information it has received from the NSX-T control cluster. The system can select an arbitrary ESXi host transport node as the mediator for the source subnet if the remote mediator ESXi host node is available.


In this mode, the ESXi host transport node at the origin of the frame to be flooded on a segment sends a copy to every other ESXi host transport node that is connected to this segment.

Table 2. Design Decisions on Segment Replication Mode

Decision ID

Design Decision

Design Justification

Design Implications


Use hierarchical two-tier replication on all segments.

Hierarchical two-tier replication is more efficient by reducing the number of ESXi hosts the source ESXi host must replicate traffic to.