Update AAD Connect to include more than one forest

Important

Skype for Business Online will be retired on July 31, 2021. If you haven't upgraded your Skype for Business Online users to Microsoft Teams before that date, they will be automatically scheduled for an assisted upgrade. If you want to upgrade your organization to Teams yourself, we strongly recommend that you begin planning your upgrade path today. Remember that a successful upgrade aligns technical and user readiness, so be sure to leverage our upgrade guidance as you navigate your journey to Teams.

Azure AD Connect supports syncing from multiple forests. However, it supports only one instance of Azure AD Connect syncing to AAD. Therefore, in cases where Azure AD is already installed in one forest, the existing instance of AAD Connect must be updated to sync from the additional forest.

  • If all identities are represented only once across both forests (that is, you haven’t made any mail-enabled contacts), then you can simply re-run the AAD Connect wizard, choose “Customize synchronization options,” and then on the Connect Your Directories page, enter the name of the additional forest and creds.

    The Connect your directories page.
  • However, if users can exist in more than one directory and you’ll be merging the data (for example, if contact objects exist in a forest corresponding to users in another forest), you will need to uninstall Azure AD Connect and re-install it. This is because the cross-forest join rules condition can only be configured during the first install. This is done on the following page:

    The Uniquely identifying your users page.

See also

Cloud Consolidation for Teams and Skype for Business