Specifies the sites for which the global catalogs (GC) should register site-specific GC locator DNS SRV resource records. ...

"Specifies the sites for which the global catalogs (GC) should register site-specific GC locator DNS SRV resource records. These records are registered in addition to the site-specific SRV records registered for the site where the GC resides, and records registered by a GC configured to register GC Locator DNS SRV records for those sites without a GC that are closest to it. 

The GC Locator DNS records and the site-specific SRV records are dynamically registered by the Net Logon service, and they are used to locate the GC. An Active Directory site is one or more well-connected TCP/IP subnets that allow administrators to configure Active Directory access and replication. A GC is a domain controller that contains a partial replica of every domain in Active Directory.

To specify the sites covered by the GC Locator DNS SRV records, click Enabled, and enter the sites' names in a space-delimited format.

If this setting is not configured, it is not applied to any GCs, and GCs use their local configuration."