If you cannot sign into devices in a newly added forest, what should you configure to resolve this issue?

When dealing with sign-in issues in a newly added forest, configuring the trust relationship is essential. Trust relationships allow for the sharing of resources and authentication between different Active Directory forests. If a forest has been added but there’s no established trust, users in one forest will not be able to authenticate against resources that are located in the other forest.

By establishing a trust relationship, you enable users and resources from different forests to communicate securely and authenticate with each other. This interconnectivity is crucial for maintaining access across environments, particularly in complex network architectures where multiple forests are employed.

The other options, while important in their own right, do not address the specific issue of authentication across two forests. Adjusting security group permissions could help manage access within a single forest but won’t resolve cross-forest sign-in issues. Similarly, subnet configuration and network connectivity are essential for overall network functionality but do not directly influence the authentication process across forests. Thus, ensuring that a proper trust relationship is in place is the key solution for enabling sign-in capabilities in a newly added forest.