Hi,
I assume you're trying to configure remote authentication against an LDAP database for administrative access to LTM? Which LTM version are you running?
You can check the online help for details:
https://LTM_ADMIN_IP/tmui/help/en/tmui/system/user/authconfig.jspad_auth
Bind
Specifies the connection settings for the Active Directory server.
* DN: Specifies the distinguished name for the Active Directory server user ID. The BIG-IP LDAP client authentication module does not support LDAP servers that do not perform bind referral when authenticating referred accounts. Therefore, if you plan to use LDAP or Active Directory as your authentication source and want to use referred accounts, make sure your LDAP servers perform bind referral.
This post also has some additional examples:
Configuring Active Directory Authentication for BIG-IP Configuration Utility
http://devcentral.f5.com/Default.aspx?tabid=53&forumid=25&tpage=1&view=topic&postid=26355 (
Click here)
Aaron