To clarify the versioning requirements between vCenter and ESXi

Symptoms:

• Discrepancies in reporting between ESXi and vCenter
• Slow updates from the Hosts to vCenter.

VMware vSAN 5.5.x
VMware vCenter Server Appliance 6.0.x
VMware vSAN 6.2.x
VMware vCenter Server 6.5.x
VMware vSAN 6.6.x
VMware vCenter Server Appliance 5.0.x
VMware vCenter Server 6.0.x
VMware vSAN 6.0.x
VMware vCenter Server Appliance 5.1.x
VMware vCenter Server 7.0.x
VMware vSphere ESXi 5.5
VMware vCenter Server Appliance 6.7.x
VMware vCenter Server 5.0.x
VMware vSAN 6.7.x
VMware vCenter Server Appliance 5.5.x
VMware vSAN 7.0.x
VMware vSphere ESXi 5.0
VMware vSAN 6.5.x
VMware vCenter Server Appliance 6.5.x
VMware vCenter Server 6.7.x
VMware vSphere ESXi 6.5
VMware vCenter Server 5.1.x
VMware vCenter Server 5.5.x
VMware vSAN 6.1.x
VMware vSphere ESXi 6.0
VMware vSphere ESXi 6.7
VMware vCenter Server Appliance 5.0
VMware vSphere ESXi 5.1
VMware vSphere ESXi 7.0.0

Communication between ESXi and vCenter is critical for VMware environments and build compatibility is key to reliable functionality.  Code updates resolve known issues and enhance communication between related products.
 
For more detailed information regarding best practices for upgrading the environment see the following KBs:

• Update sequence for vSphere 6.0 and its compatible VMware products
• Update sequence for vSphere 6.5 and its compatible VMware products
• Update sequence for vSphere 6.7 and its compatible VMware products
• Update sequence for vSphere 7.0 and its compatible VMware products

 
vSAN
The health check feature of vSAN relies heavily on vCenter & ESXi communication and requires that vCenter be equal to or newer than the ESXi hosts for reliable communication.  

vXRail
As VXRail is built upon vSAN, it carries similar requirements for vCenter.
 
See “Correlating build numbers and versions of VMware products”  for details about released versions of VMware products.
 

Verify that the vCenter version is equal to or greater than the ESXi version.

See Correlating build numbers and versions of VMware products for details regarding product interoperability requirements

• After opening the KB, then select VMware vCenter Server, find the Build number, make note of the version
  • Build numbers and versions of VMware vCenter Server
• After opening the KB, then select VMware ESXi/ESX,  find the Build number, make note of the version
  • Build numbers and versions of VMware ESXi/ESX

Note: Please verify that all the products are compatible with the version of vCenter when planning updates by using the Interoperability guide

Impact/Risks:
In rare cases, ESXi hosts on a newer version than vCenter may not properly process the unicast agent updates. This can result in a vSAN network partition.