When you first install XenServer, a user account is added to XenServer automatically. This account is the local super user (LSU) , or root, which is authenticated locally by the XenServer computer. You can create additional users by adding Active Directory accounts from the Users tab in XenCenter. (Note that the term “user” here refers to anybody with a XenServer account, that is, anyone administering XenServers, regardless of level of their role.) If you want to have multiple user accounts on a server or a pool, you must use Active Directory user accounts for authentication. This lets XenServer users log in to the servers in a pool using their Windows domain credentials.

Note: Mixed-authentication pools are not supported (that is, you cannot have a pool where some servers in the pool are configured to use Active Directory and some are not).

All editions of XenServer can add user accounts from Active Directory. However, only XenServer Enterprise and Platinum editions let you assign these Active Directory accounts different levels of permissions depending on the user’s role, using the Role Based Access Control (RBAC) feature. If you do not use Active Directory in your environment, you are limited to the LSU account.

The permissions assigned to users when you first add their accounts varies according to your version of XenServer:

• In the XenServer and XenServer Advanced editions, when you create (add) new users, XenServer automatically grants the accounts access to all features available in that version.
• In the XenServer Enterprise and Platinum editions, when you create new users, XenServer does not assign newly created user accounts roles automatically. As a result, these accounts do not have any access to the XenServer pool until you assign them a role.

AD authentication in a XenServer environment

Even though XenServers are Linux-based, XenServer lets you use Active Directory accounts for XenServer user accounts. To do so, it passes Active Directory credentials to the Active Directory domain controller.

When added to XenServer, Active Directory users and groups become XenServer subjects, generally referred to as simply users in XenCenter. When a subject is registered with XenServer, users/groups are authenticated with Active Directory on login and do not need to qualify their user name with a domain name.

Note: By default, if you did not qualify the user name (for example, enter either mydomain\myuser or myser@mydomain.com), XenCenter always attempts to log users in to Active Directory authentication servers using the domain to which it is currently joined. The exception to this is the LSU account, which XenCenter always authenticates locally (that is, on the XenServer) first.

The external authentication process works as follows:

1. The credentials supplied when connecting to a server are passed to the Active Directory domain controller for authentication.
2. The domain controller checks the credentials. If they are invalid, the authentication fails immediately.
3. If the credentials are valid, the Active Directory controller is queried to get the subject identifier and group membership associated with the credentials.
4. If the subject identifier matches the one stored in the XenServer, the authentication is completed successfully.

When you join a domain, you enable Active Directory authentication for the pool. However, when a pool is joined to a domain, only users in that domain (or a domain with which it has trust relationships) can connect to the pool.