10 Domain Trusts Best Practices

Domain trusts are an important part of Active Directory (AD) and allow for the secure sharing of resources between domains. They can be used to extend the security perimeter of an organization beyond the traditional network boundary.

Domain trusts can be complex to configure and manage. This article discusses 10 best practices for configuring and managing domain trusts.

1. Use a two-way forest trust

A two-way Forest trust allows both sides of the trust relationship to access resources in the other domain. This is important because it allows for a more seamless user experience, as users will be able to access resources in either domain without having to log in again.

It also allows for better security, as each side of the trust can control what the other side has access to. This means that if one side of the trust is compromised, the other side will still be protected.

Finally, a two-way Forest trust is easier to manage than a one-way trust. This is because there is only one trust relationship to manage, rather than two.

2. Don’t use selective authentication

Selective authentication is a security feature in Active Directory that allows an administrator to restrict which computers and users can access resources in another domain. For example, if you have a child domain called “sales” and a parent domain called “corp,” you could use selective authentication to allow only certain users in the “sales” domain to access resources in the “corp” domain.

While this may seem like a good idea at first, it can actually create more problems than it solves. The biggest problem is that it creates a single point of failure –– if the connection between the two domains is lost, then no one in the “sales” domain will be able to access any resources in the “corp” domain.

It’s much better to use a multi-master replication model, where each domain has its own copy of the data. This way, if the connection between the two domains is lost, the data is still available in both domains.

3. Do not allow users to authenticate across domains

When a user authenticates across domains, they are essentially giving their credentials to another domain. This means that if the other domain is compromised, your domain will be as well. Additionally, it can be difficult to track which users have authenticated across domains, making it more difficult to manage permissions and control access.

Therefore, it’s important to only allow authentication within a single domain. This will help to keep your domain more secure and easier to manage.

4. Limit the number of trusts between forests

The more trusts you have, the more complex your environment becomes. This complexity can lead to problems such as:

– Difficulty in troubleshooting issues
– Increased risk of security breaches
– Inefficient management of user accounts

It’s important to note that one-way trusts are less risky than two-way trusts. One-way trusts allow users in one forest to access resources in another Forest, but not vice versa. Two-way trusts allow users in both Forests to access resources in either Forest.

When possible, it’s best to use a single, two-way trust between two Forests. This will simplify your environment and reduce the risk of problems.

5. Use DNS suffix search lists

When a user attempts to access a resource on a network, their computer will first check its DNS cache for the IP address of the server hosting the resource. If the DNS cache doesn’t contain the IP address, the computer will then check its HOSTS file. If the HOSTS file doesn’t contain the IP address, the computer will finally check its DNS suffix search list.

The DNS suffix search list is a list of domain names that the computer will use to resolve the name of the server. For example, if the DNS suffix search list contains the domain names “example.com” and “example.net”, and the user attempts to access the server “www”, the computer will first try to resolve the name “www.example.com” and then “www.example.net”.

Using a DNS suffix search list has several advantages. First, it can speed up name resolution because the computer won’t have to check each domain individually. Second, it can provide redundancy in case one of the domains is unavailable. Finally, it can improve security by preventing users from accessing servers in unauthorized domains.

To configure a DNS suffix search list, open the Network Connections control panel and select the Properties of the appropriate connection. Select the TCP/IP protocol and click the Properties button. Enter the desired domain names in the DNS Suffix Search List field.

6. Configure a one-way outgoing external trust

When you create a two-way trust relationship, your domain gives the other domain’s users the same level of access to resources that your own users have. This means that if there are any malicious users in the other domain, they could potentially gain access to sensitive data or wreak havoc on your network.

A one-way outgoing external trust relationship is much more secure, because it only allows users in your domain to access resources in the other domain. This means that even if there are malicious users in the other domain, they won’t be able to access your data or systems.

To configure a one-way outgoing external trust relationship, you’ll need to use the Active Directory Domains and Trusts snap-in. Once you’ve launched the snap-in, right-click on your domain and select Properties. Then, click the Trusts tab and click the New Trust button.

On the New Trust Wizard, select External Domain and click Next. On the next page, enter the name of the other domain and click Next. On the Direction of the Trust page, select Outgoing and click Next. On the Sides of the Trust page, select One-way: Outgoing and click Next.

On the Outgoing Trust Authentication Level page, select Do not allow authentication unless all signed with a trusted certificate and click Next. On the Name of the Trust page, enter a name for the trust and click Next. On the Summary page, review your settings and click Next. On the Completing the New Trust Wizard page, click Finish.

7. Configure a one-way incoming external trust

When an attacker gains control of a user account in one domain, they can use that account to access resources in other domains. To prevent this type of attack, you should configure a one-way incoming external trust from the resource domain to the user domain. This will allow users in the user domain to access resources in the resource domain, but not vice versa.

One-way trusts are also more secure than two-way trusts because they limit the number of ways an attacker can gain access to resources in another domain. For example, if you have a two-way trust between Domain A and Domain B, an attacker who compromises a user account in Domain A can use that account to access resources in Domain B. But if you have a one-way trust from Domain A to Domain B, the attacker would need to compromise a user account in both Domain A and Domain B to access resources in Domain B.

Configuring a one-way incoming external trust is a best practice for security and it’s also required by many compliance standards, such as PCI DSS and HIPAA.

8. Configure a shortcut trust

A shortcut trust is a two-way, transitive trust relationship between two Active Directory domains that reduces the number of hops that authentication requests must take to reach their destination. By configuring a shortcut trust between two domains, you can reduce the number of domain controllers that need to be contacted for authentication requests, which can improve performance.

Shortcut trusts are particularly useful in large organizations with multiple Active Directory domains. In these organizations, it’s not uncommon for authentication requests to have to traverse multiple domain controllers before reaching their destination. By configuring shortcut trusts, you can reduce the number of domain controllers that need to be contacted, which can improve performance.

9. Configure a realm trust

A realm trust is a two-way, transitive relationship between two Active Directory forests. In other words, it’s a relationship in which both domains trust each other and any domain that either of them trusts. This type of trust is typically used when you need to share resources between two separate organizations, such as when you’re sharing resources with a partner organization or with another company that’s part of your group.

Configuring a realm trust is a bit more complex than configuring a one-way or two-way external trust, but it’s well worth the effort. By taking the time to configure a realm trust, you can be sure that both domains will be able to access the resources they need without any issues.

10. Configure a transitive forest trust

Transitive trusts simplify the management of trust relationships by allowing you to create a single trust relationship that can be used to access resources in multiple domains. This is in contrast to non-transitive trusts, which require a separate trust relationship for each domain.

Transitive trusts also provide a higher level of security than non-transitive trusts. With a transitive trust, if Domain A trusts Domain B and Domain B trusts Domain C, then Domain A automatically trusts Domain C. This means that if Domain B were to be compromised, Domain C would still be protected.

To configure a transitive Forest trust, you’ll need to use the Active Directory Domains and Trusts console. To do this, open the console and select the domain you want to create the trust relationship for. Then, right-click the domain and select Properties.

On the Properties page, select the Trusts tab. From here, you can click the New Trust button to launch the New Trust Wizard.