If not assigned and the TolerateMaximumViolations in _tolerateMaximumViolationsIn Rule has not been violated, then the root will be used if the firewall is hosted in a web application.
Requirements
Target Platforms: Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2