The Delphix Engine could send the following alert:
Description An NDMP error occurred while establishing a session from server "184.108.40.206": failed to decode message Severity CRITICAL Hostname host Timestamp 2015-08-28 04:29:52.842
This alert is common when a Network Security Scanner connects to the Network Data Management Protocol (NDMP) port without establishing a valid session. This scenario is caused by settings outside of the Delphix Engine itself. As such, changes would need to be made on the remote machine in order to resolve this alert.
Examine the machine at the IP address specified by the alert message to determine how to address the error as this is outside of Delphix.