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

The following options are available for BUM replication on logical switches.

Table 1. BUM Replication Mode of NSX-T Logical Switches

BUM Replication Mode

Description

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.

Head-End

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

Table 2. Design Decisions on Logical Switch Replication Mode

Decision ID

Design Decision

Design Justification

Design Implications

NSXT-VI-SDN-013

Use hierarchical two-tier replication on all logical switches.

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

None.