Summary: When a NetInstall process begins (Agent, Service, Installer, Manager, etc.) that process reads the list of sites contained in the NCP file to determine what site the client belongs to. Since it is possible for a client to fit the definition of multiple sites and will select the first site it finds it is important to know the order in which the sites are read.
Discussion: Reading and evaluation of the site structure follows a strict rule involving the type of object read (Organizational Unit (OU) vs. Site) and the name of the object.
The Process Reading starts at the ORG level of the site structure and all objects at the ORG are sorted in alphabetical order. If the first object in the sort is determined to be a site then the definition of that site is read and evaluated then the next object in the sort is read. This pattern continues until an OU is found or an OU was the first object found after the ORG level sort. At that point the contents of that OU are sorted alphabetically and the above pattern starts over again.
Once all sites in an OU are evaluated the site determination process backs up to the next highest level and reads the next unevaluated object. If that object is an OU the above pattern continues. This cyclical pattern of reading an OU’s contents and then backing up to the next highest unevaluated object continues until all sites have been evaluated.
As you can see the naming of objects in the site structure plays a large roll in the order of site evaluation. Here are a few example site structures and the order of evaluation.