HCX Network Extension is allowed or prevented under certain conditions.
Detected and Restricted Source Network Types
The HCX Network Extension service detects and prevents several non-supported Network Extension scenarios (items are dimmed in the Network Extension UI):
vSphere infrastructure networks (ESXi VMkernel networks).
HCX Network Profile networks (Distributed Port Groups or Segments selected in a Network Profile).
Trunk networks (Distributed Port Groups with VLAN type Trunk).
Untagged Distributed Port Groups (Distributed Port Groups with VLAN type None, ID 0 or NULL).
Private VLAN (PVLAN) networks.
Port groups configured with ephemeral binding.
Unsupported Source Configurations
HCX Network Extension does not support the following source configurations:
vSphere Standard Switch (VSS) networks.
Cisco Nexus 1000v or other third-party switches.
Cisco Application Centric Infrastructure (ACI) with VMware Virtual Machine Monitor (VMM).
vSphere Distributed Switches configured with LACP.
Virtual machine networks must only be extended with a single solution. HCX does not support Network Extension for networks already extended to the same NSX router by an external solution. For example, either HCX Network Extension or NSX L2 VPN can be used to provide connectivity, but both must not be used simultaneously. Using multiple bridging solutions simultaneously can result in a network outage.
Virtual machine networks with shared or overlapping VLAN configurations should not be extended to the same destination router. This can result in a network outage.
Secondary subnets in a single layer-two network.
Unsupported Destination Configurations
HCX Network Extension does not support the following destination configurations:
NSX-T Global Federation configurations.
HCX does not integrate with the NSX Global Manager (only the NSX Local Manager).
HCX supports one Network Extension to a maximum of 3 distinct destinations or routers.
One HCX Network Extension configuration cannot be extended multiple times to the same destination router.
Daisy-chaining a single network to two sites (A to B to C) is supported. Daisy-chaining a single network to three destination sites (A to B to C to D) is not supported.
One HCX Network Extension appliance can only connect to one Distributed Virtual Switch or NSX Transport Zone.
Networks can only be extended between one appliance pair (source and destination appliances) per site; multiple network appliances cannot be used to increase thoughput.
HCX Network Extension does not detect or mitigate loops.
Virtual machine networks that span more than one vCenter Server should not be extended from more than one vCenter to the same destination router. This can result in a network outage.
HCX Network Extension does not detect or mitigate IP conflicts.
HCX Network Extension does not detect or mitigate MAC conflicts.
For a cloud/site pair, a given network can be extended through only one appliance and is subject to the resource and the performance limitations of that appliance.
HCX Network Extension connects to an existing segment on the target site if it has the same gateway IP and Prefix configured for the extension, and it disconnects the NSX router interface from the network. If the NSX tier-1 router interface was previously connected and in service, all communication to the gateway on that cloud network will be disrupted.