which driver i need to configure to connect external edirectory ldap sever.
IDM is funny, since you would think eDir would be the easiest driver being what it runs on. And yet...
The answer is, it depends. Do you need bidir password sync? Is this mostly a push to the remote eDir? Or is this a full bidirectional connection?
The BiDir eDir is basically an LDAP driver, using a changelog module for eDir (based on dxevent, the core of IDM). The original eDir driver was two drivers, one half in each of the trees. More complicated and harder to understand. Most everything happens on the Publisher channel of each driver, inbound.