Before discussing where to bind to begin a search for objects in a domain, here is some information about how data is stored in Active Directory.
If you have a forest with more than one domain, Active Directory does not store all object data on a single domain controller — for performance, scalability, and reliability reasons. A domain controller holds all information about the domain that it is a member of (it has a full replica of the domain). But a domain controller does not hold complete information about any other domain.
So, if you bind to the domain object (with referral chasing turned off — For more information, see Referrals), you can search for any object in that domain (and only that domain). The search can retrieve any property and can use a query filter containing any property.
In a forest, domains are arranged hierarchically as domain trees. A domain tree can be just a single domain or a domain with one or more child domains. These child domains, in turn, can have child domains beneath them and so on. A domain tree is also a contiguous namespace. A contiguous namespace means that the child domains are a continuation of the naming hierarchy. For example, a domain fabrikam.com (or DC=Fabrikam,DC=COM) can have a child domain named mydivision (mydivision.fabrikam.com or DC=mydivision,DC=Fabrikam,DC=COM), which in turn could have a child domain named mydev (mydev.mydivision.fabrikam.com or DC=mydev,DC=mydivision,DC=Fabrikam,DC=COM).
So, if you bind to a domain object (with referral chasing turned on) for a domain within a domain tree, you will search that domain and the entire hierarchy below it. The search can retrieve any property and can use a query filter containing any property.
If a domain controller contains a full replica of only its own domain, how can you perform a subtree search on a domain tree? A domain holds references to its child domains. When a domain controller processes a subtree search request against its own domain, the domain controller searches that domain and then returns referrals to each of its child domains to the client. A referral is the way that a directory server communicates that it does not contain the information required to complete a request (such as a query) but has a reference to a server that may contain the required information. In the case of a subtree search of a domain tree, a referral is returned for each direct child domain so that the search can be continued at a domain controller in each child domain. If referral chasing is turned on, the LDAP client library (Wldap32.dll) uses those referrals to bind to a domain controller in each child domain and continue the search. If referral chasing is turned off, the LDAP client does not resolve the referrals and the search is complete.
A subtree search on a domain tree with referral chasing turned on can be time-consuming if there is a slow connection to the domain controllers for the child domains. If you want to search only a single domain, you should turn referral chasing off to avoid having to search the child domains unnecessarily.