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10 things about AD domain trusts

Domain trusts can be complicated to administer, and it’s important to implement changes correctly the first time. Here are some key points to keep in mind to help ensure that your trusts are configured effectively with a minimum of headaches.

1: Determine what kind of trust you should use

Before deploying a domain trust, you should ensure that the type(s) used are correct for the tasks at hand. Consider the following dimensions of a trust:

  • Type: Identifies the types of domains involved in trust(s).
  • Transitivity: Determines whether one trust can let a trusted domain pass through to a third domain.
  • Direction: Identifies the direction of access and trust (trusted accounts and trusting resources).
  • 2: Get familiar with the Active Directory Domains And Trusts Console

    Trust relationships are managed via the Active Directory Domains And Trusts Console. It lets you perform these basic tasks:


    • Raise domain functional level
    • Raise forest functional level
    • Add UPN suffixes
    • Manage domain trust
    • Manage forest trust

    For details on using this tool, see “TechRepublic Guided Tour: Active Directory Domains And Trusts Console.”

    3: Know the tools

    As with most other elements of the Windows Server family, command-line tools can be used to script repetitive tasks or to ensure consistency in the case of trust creation. Some of the top tools include:

    • NETDOM: Used to establish or break trust types.
    • NETDIAG: The output of this tool can give basic status on trust relationships.
    • NLTEST: Can be used to verify a trust relationship.

    You can also use Windows Explorer to view membership to shared resources as they are assigned from trusted domains and/or forests. Active Directory Users And Computers can also provide membership details of Active Directory Objects that have members from trusted domains and/or forests.

    4: Set up a test environment

    Depending on your environment and usage requirements, a simple mishap in the creation of domain trusts can have enterprise-wide repercussions. But it’s difficult to set up a completely similar test environment to replicate multi-domain and forest issues. Having similar domain scenarios is easier to facilitate, as a means to reinforce the principles and test basic functionality. Consider also template Active Directory objects to test on the live domain relationships to ensure that the desired functionality is obtained but not exceeded before using live groups, accounts, and other objects.

    5: Review privileges

    When trusts are created, it’s important to ensure that the desired functionality is achieved. But be sure to review the configured trust to verify that the direction of access is correct. For example, if domain A needs to access only a limited amount of resources on domain B; a two-way trust would suffice. However, an administrator from domain B may be able to assign access to resources on domain A. Ensuring the desired direction, type, and transititivity of trusts is critical.

    6: Map out the trusts

    Create a map of trusts with simple arrows and boxes illustrating which domains will be trusting and trusted and which trusts will be 1-way and 2-way. Then, with the simple picture(s) in place, map out which domains will trust which–and determine the transititivity as well. This simple chart will make more sense of the greater task at hand and allow you to determine which domains need direction of access and in which direction. Some domains will simply act as a gateway for transitive access to other domains.

    7: Document trust relationships

    As organizations marry (and divorce) in today’s business world, it’s important to have clear documentation of the trust inventory–and to make sure it’s accessible without the trust or domain. For example, if you’re in Domain B and your headquarters in Domain A sells your division and breaks your trust, your concise documentation saved on a server in Domain A does you little good. Document the type of trust, transitivity, direction, business need for the trust, anticipated duration of the trust, credentials, domain/forest principal information (name, DNS, IP addresses, locations, computer names, etc.), and contact person(s) for the corresponding domains.

    8: Avoid making trust relationships too deep

    In the interest of everyone’s time, don’t nest membership more than one deep when using trusts in multiple domains and forests. Nesting membership can consolidate the number of manageable Active Directory objects, but determining actual membership administration is greatly increased.

    9: Know how to manage different versions of Windows

    When running in Windows 2000 and Windows Server 2003 native mode for Active Directory, full functionality is maintained for member domains and forests. If any NT domains or member systems are present in the enterprise, their trust entry functionality is limited by the inability to recognize the Active Directory objects. A frequent strategy in this scenario is to have “domain islands” of those that don’t connect to the more common enterprise infrastructure.

    10: Remove expired or overlapping trusts

    Changes in business organization may have left unused trusts in place on your domain. Clear out any trusts that are not actively being used. You should also ensure that the trusts you have are set up correctly for the required access and usage patterns. An audit of your trust inventory can be a strong supplement to your well-rounded security policy

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