The default behavior of Directory Server is to deny access unless there is a specific ACI that grants access. therefore, if no ACIs are defined, all access to the server is denied.
When you install Directory Server or when you add a new suffix, several default ACIs are defined automatically in the root DSE. These ACIs can be modified to suit your security requirements.
For details on the default ACIs and how to modify them, see How Directory Server Provides Access Control in Sun Java System Directory Server Enterprise Edition 6.3 Reference.