Mac support in an Active Directory environment

Editor’s Note: This story is reprinted from Computerworld. For more Mac coverage, visit Computerworld’s Macintosh Knowledge Center.

Supporting Mac users can be a challenge to systems administrators in a Windows Active Directory environment. Although Apple has used Samba to make it easy for Macs to browse and access shares and printers hosted by Windows servers using Microsoft's server message block (SMB) protocol, true Active Directory integration requires more than just access to resources.

For one thing, it requires support for an environment where users can rely on their Active Directory accounts for log-in to both Mac and Windows computers. Depending on your environment, you may also want to be able to implement security measures to limit what users may do while logged into a Mac or to manage the user experience as you would do with group policies for Windows machines.

There are a number of solutions and approaches that you can take for integrating Macs into your Active Directory infrastructure, and I'll be talking about some of them here.

Apple's Active Directory plug-in

The lowest-cost solution is to use Apple's built-in Active Directory support. Beginning in Mac OS X Panther (10.3), Apple introduced a plug-in to its Directory Access utility that allows you to configure authentication against Active Directory. Apple's Active Directory plug-in uses LDAP to query Active Directory.

The Active Directory plug-in works fairly well. It supports forests with multiple domains, domain controller fail-over and can automount a user's home directory. It can also grant users administrator access to a Mac workstation based on their Active Directory group membership. You can also enable mobile accounts for portable computers and designate a preferred domain controller if needed.

The process of using the plug-in to join a Mac to an Active Directory domain is straightforward, and is similar to joining a Windows computer to a domain. You'll need an Active Directory account with permission to join the computer to the domain; if the account was not created in advance, you'll need authority to create it. You will also need to configure the search path of available directories to include Active Directory using the Authentication tab in the Directory Access tool. Mac OS X can search multiple directory configurations in a specified path when a user attempts to log in.

Dynamic UID vs. static UID mapping

One of the hurdles to integrating Mac OS X with Active Directory is that their directory services schemas are significantly different. One of the key attributes in the Open Directory schema used by Mac OS X is the User ID number (UID). As in other Unix systems, the UID is used by the Mac OS X file system to designate file ownership and permissions both for local and remote files.

Each local or network user account used to log into Mac OS X requires a UID. But there is no directly correlating attribute in Active Directory.

Apple provides a choice of two methods to providing Active Directory users a UID attribute. The first and default option is to dynamically generate a UID for each user when they log in. When this option is used, Mac OS X generates a UID at log-in based on the GUID (Globally Unique Identifier) attribute from the user's Active Directory account and the MAC address of the Macintosh network card he is using. The second option is to choose an attribute that is included in Active Directory as the user's UID. You can map any attribute, be it one that is part of the default Active Directory schema or one that is part of a custom schema extension.

Dynamic UID generation is much easier and requires no action on the part of the systems administrator. However, it isn't perfect. Each time a user logs in on a different Mac, he will have a different UID. This can be problematic if you have any Mac servers (or even individual Macs with file sharing enabled) because user access to files on those servers will change each time they use a different computer despite the fact that they are using the same Active Directory account.

Using a static UID by mapping it to an attribute in Active Directory prevents these potential issues, and it may be a solution that you have already implemented for other Unix systems in your network. However, it requires more effort. If you choose to map to an existing attribute, you will need to manually populate this number in each user account that will be used for Mac log-in. This can be a tedious process. If you choose to use an existing attribute rather than extend Active Directory's schema, you'll lose the ability to use that attribute for another purpose.

Thursby's ADmitMac

ADmitMac by Thursby Software Systems offers several features that Apple's Active Directory plug-in and Samba configuration do not. Like Apple's solution, ADmitMac is based around a Directory Access plug-in.

Most notably, ADmitMac fully supports Kerberos under Active Directory as well as signed LDAP and SMB communication and NT LAN Manager, enabling much tighter security with Windows 2003 Server. As such, it doesn't require you to lower the default security settings of Windows 2003 Server. Apple's solutions require unsigned LDAP and SMB communication.

In addition to enhanced security, ADmit Mac supports the Windows Distributed File System and long share names, and provides additional options for browsing a Windows Server network for shares and printers. A specialized version is also available with support for the Common Access Card smart card standard.

ADmit Mac also provides some other advantages. First, it offers an Active Directory management console for Mac OS X that allows administrators to reset user passwords, move users and computers and create or modify existing accounts much as they would using the Microsoft Management Console. Second, it offers more options than Apple's solution for how network and local home directories are managed. Particularly helpful on this front is a tool that can be used to move a local Mac user's home folder to a network location and associate it with an Active Directory account. This can make the transition to Active Directory integration much easier for end users.

Also, ADmitMac supports an Apple-managed client environment. Like group policies in Active Directory, Mac OS X's managed client environment -- sometimes referred to as MCX -- allows administrators to restrict access to Mac OS X system components and to create a highly customized user experience. ADmit enables several of Apple's client management features and does so using Mac OS X Server's Workgroup Manager.

To do so, ADmit Mac creates a file stored on a Windows share within the domain to hold all the MCX user information that would normally be stored in an Open Directory domain hosted by Mac OS X Server. However, Thursby's own documentation admits that its client management approach isn't perfect and that some actions may result in unexplained error messages or simply may not function without any indication of an error.

Centrify's Direct Control for Mac

Centrify's Direct Control is a series of solutions for integrating diverse platforms with Active Directory, including Mac OS X.

Direct Control installs as a Directory Access plug-in under Mac OS X. When the server-side solution is installed on Windows domain controllers, it adds a series of group policy objects (GPOs) that can be used to manage the Mac environment. Direct Control offers a range of GPOs for security and user experience settings -- many of which mirror the options available using Mac OS X Server's Workgroup Manager tool. It does this by integrating a local registry file copied to the Mac with Apple's MCX architecture. Direct Control also offers the ability to use smart cards for authentication.

Direct Control offers the simplest and most full-featured Active Directory integration solution for Mac OS X. Because it relies on Active Directory's group policy architecture, it functions more seamlessly for managing access than does Thursby's ADmitMac, particularly for systems administrators who are unfamiliar with Mac OS X.

Also impressive: It succeeds without modifying the Active Directory schema. It does not, however, offer the security of signed SMB connections, although it does support encrypted LDAP queries. It also works well with products such as Thursby's DAVE to enable signed SMB communication as well as with third-party server-side solutions that support Mac OS X's Apple Filing Protocol, which offers greater security than unsigned SMB.

Using Mac OS X Server for additional client management

If you want to take full advantage of Apple's client management architecture, the best solution is to implement Mac OS X Server in your Active Directory environment. This can be the most challenging method of adding support for Mac OS X because Active Directory and Open Directory, Mac OS X Server's native directory service, have very distinct schemas. They also share three matching attributes: username, password and home directory. This can make creating a fully integrated infrastructure a very big challenge because it requires extending the schema of one or both platforms.

There is a method of offering partial Mac client management and access to other Mac OS X Server services under Active Directory that doesn't require schema modification. The approach is twofold. First, join Mac servers and clients to Active Directory using Apple's Active Directory plug-in. Second, create a directory search path on Mac servers and clients that searches both the Active Directory domain and an Open Directory domain hosted by one or more Mac servers.

This configuration allows you to create computer lists in the Open Directory domain that contain Mac computer accounts from Active Directory. Management settings can then be enforced on those computer lists using Mac OS X Server's Workgroup Manager with no further configuration.

The same approach can be extended to groups of users by creating group accounts in the Open Directory domain and populating them with user accounts from Active Directory. This method isn't perfect, and some client management functions may not respond properly, but it requires significantly less effort than modifying the Open Directory and/or Active Directory schemas. It can function as a temporary solution if you are planning to extend the schema but require an immediate solution while you do so.

What about Services for Mac?

Windows Server includes Services for Mac (SFM) -- optional components that provide the ability to create and manage shares and print queues using the Apple Filing Protocol (AFP) and the defunct AppleTalk protocol. Services for Mac is a solution that was designed to work with the classic Mac OS versions -- in other words, those before Mac OS X.

Its security options rely on a Microsoft user authentication module being installed on Mac clients, a version of which was never developed for Mac OS X. As such, the only way to support Mac OS X access to SFM shares and print queues is by using clear text passwords or the limited encryption of an older version of the AppleShare protocol.

Given Apple's longstanding inclusion of Samba in Mac OS X and the security limitation, it has been quite some time since SFM was considered a terribly solid solution. SFM also suffers from performance issues because of its design and the fact that it relies on the outdated AppleTalk protocol.

That said, there are alternate third-party AFP servers for Windows Server, including the robust ExtremeZ IP by Group Logic and MacServerIP by Cyan Software.

These products offer enhanced security options but they also offer one other feature that can be important for some Mac users. Mac files contain a resource fork as part of their structure; this fork is not supported by either NTFS or FAT file systems. When working with SMB-mounted drives, Mac OS X typically performs a translation of the resource fork into a separate file to work around this issue.

For most applications, this functions very well. However, some applications encounter problems with this approach. In those situations, having an AFP server solution can result in a more seamless workflow.

Ryan Faas is a freelance writer and technology consultant specializing in Mac and multiplatform network issues. In addition to writing for Computerworld, he is a frequent contributor to InformIT.com. Ryan was also the co-author of O'Reilly's "Essential Mac OS X Panther Server Administration." You can find more information about Ryan, his consulting services and recently published work at www.ryanfaas.com and can e-mail him at ryan@ryanfaas.com.

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