Whenever a client needs to download a new operating system or just the bits of an application or a package, it needs to contact a distribution point on the site. It is important to note how a client locates its distribution point, this is done by creating boundaries.
In Configuration Manager 2012, we have to define a boundary or multiple boundaries and place them within a boundary group. Within these groups we define which content servers should be available for clients within the boundaries. Boundaries are used to make the client select the closest server from which the content is to be transferred.
Under the properties of the Boundary Group -My Site Properties page we can define which content servers are available for clients. Also, we can define it for a site assignment as shown in the following screenshot: