Something that is sort of outside the scope of this book, but is relevant here, is Active Directory Sites and Services. Inside any Active Directory environment, your DCs will automatically have this tool installed, called AD Sites and Services. The purpose here is to define your physical locations of the network, sites, if you will. The many small businesses have only a single site, and often they never have to even open this tool. Makes sense, as everything is always connected to the same site. However, as soon as you grow your business and expand to a second location, the network typically gets much more complex, and you now have IP subnets that are different between the two sites. Active Directory Sites are defined by what IP address space, or subnet, a computer is currently residing in. When your computer checks in with AD, it is automatically known what site you are part of based on the IP address of your computer.

Here is a quick picture of Active Directory Sites and Services, so you can see the layout and also see that the different sites are defined by which IP addressing spaces they contain:

Once your environment is large enough and you have defined your Sites inside this tool, you have now enabled Group Policy to be able to issue settings to computers (and users) based on the site that they reside in. Users follow the computers in this scenario. If a computer account is logging in and Group Policy recognizes it to be in the GrandRapids site, it will apply all GPO settings that are flagged for GrandRapids. The same is true of any users that log into that computer; since the computer is currently sitting in GrandRapids, any user-based policies that are filtered for GrandRapids will also apply.