NSX Logical Switch

Logical Switch:

  • Logical Switch also known as NSX virtual switch does additional functionality from the tradition virtual switches.
  • Logical Switch is a data plane component of NSX.
  • The key feature the logical switch offers is the VXLAN functionality which the tradition virtual switch does not have.

I have covered the details of the VXLAN in the below blog.


  • Logical switch is distributed in nature.
  • Logical Switch is a software kernel based & it is deployed to a virtual Distributed Switch (vDS) & works as extensions to the vDS.
  • When a logical switch is created, it creates a corresponding port group in the vDS.



    • It is referred as “virtualwire” & a unique VNI (Virtual Network Identifier) is assigned to each logical switch.
    • Logical switches use VNIs instead of instead of VLAN numbers. There is always 1:1 relation between the Logical Switch & the VNI number,
    • VNI is similar to the VLAN ID representing the Ethernet broadcast domains. It identifies to which segment that the Ethernet frames belongs to.
    • VNI number ranges from 5000 ~ 16777215

Transport Zone:

Each Logical switch is associated with a Transport Zone. (LS can be part of only 1 Transport Zone)

  • Transport Zone controls to which hosts a logical switch can be part of.
  • Transport Zone can span across one or more vSphere clusters.
  • Transport zones dictate which clusters and, therefore, which VMs can participate in the use of a particular network.
  • The communication happens over the VXLAN Tunnel Endpoints (VTEPs).

Transport Zone can be either Global Transport Zone or Universal Transport Zone.

  • Global Transport Zone is created for the group of ESXi host clusters under the same NSX domain. These are local to vCenter.
  • Universal Transport Zone is created for the group of ESXi host cluster under cross vCenter domain.

What is Universal Logical Switches?

  • With NSX 6.2 new functionality has been introduced called Universal Logical Switch (ULS)
  • This functionality is introduced as part of Cross vCenter functionality allowing the logical switches to span across multiple vCenter’s.
  • ULS allows Layer 2 network to span across multiple sites.

* This is the key difference between the Logical Switch & the Universal Logical Switch.

  • Universal Logical Switch (ULS) is associated with the Universal Transport Zone.


    • When the Logical Switch is added to the Universal Transport Zone it becomes Universal Logical Switch.
    • The ULS is available on all the clusters of the Universal Transport Zone.
    • Universal Transport Zone span across clusters from any vCenter.
  • VNI (Segment ID) number for the ULS should be configured in such a way that it is not overlapping with the Logical switches VNI.
  • The key use case of ULS is for the Cross vCenter & having Active-Active or Active-Standby workloads across different sites.


    • Workloads can be made Active – Active or Active – Standby in both the Primary & Secondary (DR) DC by having the same network extended across multiple sites.
    • This provides ease of work load mobility & seamless DR switch over in case of any trouble or issue.

There are also other universal components introduced with NSX version 6.2

  • Universal Controller Cluster (UCC)
  • Universal Logical Switch (ULR)
  • Universal Distributed Logical Router (UDLR)
  • Universal Distributed Firewall (UDFW)