On Mac OS X v10.6-based systems, the LDAP server specified via DHCP option 95 is no longer added to the search base by default.  This reduces the possibility of an unauthorized DHCP server being used to add an LDAP directory domain to the authentication search path on a client.  The new behavior locates LDAP servers via Bonjour and then places any DHCP-supplied LDAP servers at the top of the list of servers available for binding.

Excerpt from:
DHCP-provided LDAP not used for authentication in Mac OS X v10.6, Mac OS X Server v10.6

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