When joining a Windows 2000 domain to a Windows 2000 domain forest, a trust relationship is established automatically. This trust relationship is a two-way, transitive trust relationship. No administrative tasks are required to establish this trust relationship.
Trust relationships within a domain forest are established at the time that the domain is created. Once established, these trust relationships do not need to be managed. Exceptions to this are trust relationships between Windows 2000 forests, which require explicit trusts. Explicit trusts are trust relationships that are manually created by administrators, as opposed to trusts created automatically during installation of a domain controller.