To determine which domains it can access, a Connection Server instance traverses trust relationships beginning with its own domain.
For a small, well-connected set of domains, Connection Server can quickly determine the full list of domains, but the time that it takes increases as the number of domains increases or as the connectivity between the domains decreases. The list might also include domains that you would prefer not to offer to users when they connect to their remote desktops and applications.
You can use the vdmadmin command to configure domain filtering to limit the domains that a Connection Server instance searches and that it displays to users. See the Horizon 7 Administration document for more information.
If a forest trust is configured with name suffix exclusions, the configured exclusions are used to filter the list of forest child domains. Name suffix exclusion filtering is applied in addition to the filtering that is specified with the vdmadmin command.