Tip - A Quick Tip to designate a domain controller for client authentications.
This article explains the use of SRV priority. This applies to Windows 2000, Windows 2003 and Windows Server 2008.
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http://www.windowsnetworking.com/kbase/WindowsTips/WindowsServer2008/AdminTips/ActiveDirectory/AQuickTiptodesignateadomaincontrollerforclientauthentications.html