Take special care when migrating an ESX system to ESXi. On ESX, the management interface (vswif) is owned by the Service Console and any routing decision for outgoing management traffic is done using the routing table in the Service Console. VMkernel interfaces (vmknics), however, are owned by the VMkernel and any routing decision for outgoing VMkernel traffic (vMotion, FT, iSCSI and NFS) is done using the routing table in the VMkernel TCP/IP stack.
On ESX, the management interface can be in the same IP subnet as one of the VMkernel NICs without causing any issues.
ESXi does not have a Service Console. The management agents/daemons run on the VMkernel and use the VMkernel's TCP/IP stack. Therefore the management interface is just another VMkernel interface (vmknic). On ESXi, the management traffic and the VMkernel traffic use the same routing table in the VMkernel TCP/IP stack. Because of this, there is a possibility of unexpected network behavior if the management interface is on the same IP subnet as one of the other VMkernel interfaces.
Note: Having more than one vmknic using the same DHCP server for configuration leads to the same situation. VMware recommends avoiding this scenario as well.
Impact/Risks:
Deploying such a configuration can lead to unexpected results like connectivity issues, low throughput and asymmetric routing.
Configurations with more than one vmknic interface on the same IP subnet is
not supported.
For exceptions see
Considerations for using software iSCSI port binding in ESX/ESXi (2038869) and
Multiple-NIC vMotion in vSphere (2007467).