Information
Configure the ESXi host firewall to restrict access to services running on the host .
Unrestricted access to services running on an ESXi host can expose a host to outside attacks and unauthorized access. Reduce the risk by configuring the ESXi firewall to only allow access from authorized networks.
http://pubs.vmware.com/vsphere-60/topic/com.vmware.vsphere.security.doc/GUID-8912DD42-C6EA-4299-9B10-5F3AEA52C605.html
Solution
From the vSphere web client, select the host and click "Manage" -> "Settings" -> "System" -> "Security Profile".
For each enabled services for both incoming and outgoing connections set a proper network/IP Range after deselecting "Allow connections from any IP address" checkbox.