The basics of Active Directory What is Active Directory? Active Directory is Microsoft's trademarked directory service, an integral part of the Windows architecture. Like other directory services, such as Novell Directory Services (NDS), Active Directory is a centralized and standardized system that automates network management of user data, security and distributed resources and enables interoperation with other directories. Active Directory is designed especially for distributed networking environments. Active Directory was new to Windows 2000 Server and further enhanced for Windows Server 2003, making it an even more important part of the operating system. Windows Server 2003 Active Directory provides a single reference, called a directory service, to all the objects in a network, including users, groups, computers, printers, policies and permissions. For a user or an administrator, Active Directory provides a single hierarchical view from which to access and manage all of the network's resources. Why implement Active Directory? There are many reasons to implement Active Directory. First and foremost, Microsoft Active Directory is generally considered to be a significant improvement over Windows NT Server 4.0 domains or even standalone server networks. Active Directory has a centralized administration mechanism over the entire network. It also provides for redundancy and fault tolerance when two or more domain controllers are deployed within a domain. Active Directory automatically manages the communications between domain controllers to ensure the network remains viable. Users can access all resources on the network for which they are authorized through a single sign-on. All resources in the network are protected by a robust security mechanism that verifies the identity of users and the authorizations of resources on each access. Even with Active Directory's improved security and control over the network, most of its features are invisible to end users; therefore, migrating users to an Active Directory network will require little re-training. Active Directory offers a means of easily promoting and demoting domain controllers and member servers. Systems can be managed and secured via Group Policies. It is a flexible hierarchical organizational model that allows for easy management and detailed specific delegation of administrative responsibilities. Perhaps most importantly, however, is that Active Directory is capable of managing millions of objects within a single domain. Basic divisions of Active Directory
Active Directory networks are organized using four types of divisions or container structures. These four divisions are forests, domains, organizational units and sites.
Forests: The collection of every object, its attributes and attribute syntax
in the Active Directory. Domain: A collection of computers that share a common set of policies, a name and a database of their members. Organizational units: Containers in which domains can be grouped. They create a hierarchy for the domain and create the structure of the Active Directory's company in geographical or organizational terms. Sites: Physical groupings independent of the domain and OU structure. Sites distinguish between locations connected by low- and high-speed connections and are defined by one or more IP subnets.
Forests are not limited in geography or network topology. A single forest can contain
numerous domains, each sharing a common schema. Domain members of the same forest need not even have a dedicated LAN or WAN connection between them. A single network can also be the home of multiple independent forests. In general, a single forest should be used for each corporate entity. However, additional forests may be desired for testing and research purposes outside of the production forest.
Domains serve as containers for security policies and administrative assignments. All
objects within a domain are subject to domain-wide Group Policies by default. Likewise, any domain administrator can manage all objects within a domain. Furthermore, each domain has its own unique accounts database. Thus, authentication is on a domain basis. Once a user account is authenticated to a domain, that user account has access to resources within that domain. Active Directory requires one or more domains in which to operate. As mentioned before, an Active Directory domain is a collection of computers that share a common set of policies, a name and a database of their members. A domain must have one or more servers that serve as domain controllers (DCs) and store the database, maintain the policies and provide the authentication of domain logons. With Windows NT, primary domain controller (PDC) and backup domain controller (BDC) were roles that could be assigned to a server in a network of computers that used a Windows operating system. Windows used the idea of a domain to manage access to a set of network resources (applications, printers and so forth) for a group of users. The user need only to log in to the domain to gain access to the resources, which may be located on a number of different servers in the network. One server, known as the primary domain controller, managed the master user database for the domain. One or more other servers were designated as backup domain controllers. The primary domain controller periodically sent copies of the
database to the backup domain controllers. A backup domain controller could step in as primary domain controller if the PDC server failed and could also help balance the workload if the network was busy enough. With Windows 2000 Server, while domain controllers were retained, the PDC and BDC server roles were basically replaced by Active Directory. It is no longer necessary to create separate domains to divide administrative privileges. Within Active Directory, it is possible to delegate administrative privileges based on organizational units. Domains are no longer restricted by a 40,000-user limit. Active Directory domains can manage millions of objects. As there are no longer PDCs and BDCs, Active Directory uses multimaster replication and all domain controllers are peers.
Organizational units are much more flexible and easier overall to manage than domains.
OUs grant you nearly infinite flexibility as you can move them, delete them and create new OUs as needed. However, domains are much more rigid in their existence. Domains can be deleted and new ones created, but this process is more disruptive of an environment than is the case with OUs and should be avoided whenever possible.
By definition, sites are collections of IP subnets that have fast and reliable communication links between all hosts. Another way of putting this is a site contains LAN connections, but not WAN connections, with the general understanding that WAN connections are significantly slower and less reliable than LAN connections. By using sites, you can control and reduce the amount of traffic that flows over your slower WAN links. This can result in more efficient traffic flow for productivity tasks. It can also keep WAN link costs down for pay-by-the-bit services. The Infrastructure Master and Global Catalog Among the other key components within Active Directory is the Infrastructure Master. The Infrastructure Master (IM) is a domain-wide FSMO (Flexible Single Master of Operations) role responsible for an unattended process that "fixes-up" stale references, known as phantoms, within the Active Directory database. Phantoms are created on DCs that require a database cross-reference between an object within their own database and an object from another domain within the forest. This occurs, for example, when you add a user from one domain to a group within another domain in the same forest. Phantoms are deemed stale when they no longer contain up-to-date data, which occurs because of changes that have been made to the foreign object the phantom represents, e.g., when the target object is renamed, moved, migrated between domains or deleted. The Infrastructure Master is exclusively responsible for locating and fixing stale phantoms. Any changes introduced as a result of the "fix-up" process must then be replicated to all remaining DCs within the domain.
The Infrastructure Master is sometimes confused with the Global Catalog (GC), which maintains a partial, read-only copy of every domain in a forest and is used for universal group storage and logon processing, among other things. Since GCs store a partial copy of all objects within the forest, they are able to create cross-domain references without the need for phantoms. Active Directory and LDAP Microsoft includes LDAP (Lightweight Directory Access Protocol) as part of Active Directory. LDAP is a software protocol for enabling anyone to locate organizations, individuals and other resources such as files and devices in a network, whether on the public Internet or on a corporate intranet. In a network, a directory tells you where in the network something is located. On TCP/IP networks (including the Internet), the domain name system (DNS) is the directory system used to relate the domain name to a specific network address (a unique location on the network). However, you may not know the domain name. LDAP allows you to search for individuals without knowing where they're located (although additional information will help with the search). An LDAP directory is organized in a simple "tree" hierarchy consisting of the following levels:
The root directory (the starting place or the source of the tree), which branches out to Countries, each of which branches out to Organizations, which branch out to Organizational units (divisions, departments and so forth), which branch out to (include an entry for) Individuals (which include people, files and shared resources, such as printers)
An LDAP directory can be distributed among many servers. Each server can have a replicated version of the total directory that is synchronized periodically. It is important for every administrator to have an understanding of what LDAP is when searching for information in Active Directory and to be able to create LDAP queries is especially useful when looking for information stored in your Active Directory database. For this reason, many admins go to great lengths to master the LDAP search filter. Group Policy management and Active Directory It's difficult to discuss Active Directory without mentioning Group Policy. Admins can use Group Policies in Microsoft Active Directory to define settings for users and computers throughout a network. These setting are configured and stored in what are
called Group Policy Objects (GPOs), which are then associated with Active Directory objects, including domains and sites. It is the primary mechanism for applying changes to computers and users throughout a Windows environment. Through Group Policy management, administrators can globally configure desktop settings on user computers, restrict/allow access to certain files and folders within a network and more. It is important to understand how GPOs are used and applied. Group Policy Objects are applied in the following order: Local machine policies are applied first, followed by site policies, followed by domain policies, followed by policies applied to individual organizational units. A user or computer object can only belong to a single site and a single domain at any one time, so they will receive only GPOs that are linked to that site or domain. GPOs are split into two distinct parts: the Group Policy Template (GPT) and the Group Policy Container (GPC). The Group Policy Template is responsible for storing the specific settings created within the GPO and is essential to its success. It stores these settings in a large structure of folders and files. In order for the settings to apply successfully to all user and computer objects, the GPT must be replicated to all domain controllers within the domain. The Group Policy Container is the portion of a GPO stored in Active Directory that resides on each domain controller in the domain. The GPC is responsible for keeping references to Client Side Extensions (CSEs), the path to the GPT, paths to software installation packages, and other referential aspects of the GPO. The GPC does not contain a wealth of information related to its corresponding GPO, but it is essential to the functionality of Group Policy. When software installation policies are configured, the GPC helps keep the links associated within the GPO. The GPC also keeps other relational links and paths stored within the object attributes. Knowing the structure of the GPC and how to access the hidden information stored in the attributes will pay off when you need to track down an issue related to Group Policy. For Windows Server 2003, Microsoft released a Group Policy management solution as a means of unifying management of Group Policy in the form of a snap-in known as the Group Policy Management Console (GPMC). The GPMC provides a GPO-focused management interface, thus making the administration, management and location of GPOs much simpler. Through GPMC you can create new GPOs, modify and edit GPOs, cut/copy/paste GPOs, back up GPOs and perform Resultant Set of Policy modeling.
DNS and Active Directory Active Directory and the Domain Name System (DNS)
What is DNS? One can define the domain name system as the way that Internet domain names are located and translated into Internet Protocol addresses. A domain name is a meaningful and easy-to-remember "handle" for an Internet address. Active Directory relies heavily on DNS to function, but not just any DNS. Active Directory is highly dependent on the Microsoft DNS service found on Windows 2000 Server or Windows Server 2003 systems or equivalents. However, though not highly recommended, it is possible integrate a non-Microsoft DNS to use with Active Directory. Microsoft first introduced a DNS service with Windows NT Server 4.0. However, that early version of DNS from Microsoft is not capable of supporting Active Directory. Windows NT Server 4.0 DNS lacks three specific features: Service Resource Records (SRV RR), Dynamic DNS (DDNS) and Incremental Zone Transfers (IXFR). Without these DNS features, Active Directory cannot function. Therfore, it is essential to understand how DNS works. DNS is extremely important to all aspects of proper Active Directory operation. Any time a client makes a request for a domain service, it must find a domain controller to service that request, which is where DNS comes in to play. There are two types of DNS queries: recursive and iterative. When a DNS client requests DNS information, it uses a recursive query to do so. (And for the purposes of this discussion, a DNS client is any computer requesting DNS information, even if that computer happens to be running a server operating system.) In a recursive query, the DNS client sends its query to the first DNS server that it has been configured for in its TCP/IP configuration. It then sits and waits for the server to return an answer. If the server returns a positive response, the client will then go to the IP address returned by the server. If it's a negative response, the client will return some sort of "Page/Resource not found" error to the user. One thing that's important to note here is that configuring multiple DNS servers on a client will not cause the client to check with subsequent servers if the first one returns a negative response. The only time a client will go to its secondary DNS server is if the first one is unavailable. If the first DNS server queried returns a negative response, the client will not try any secondary servers and will accept that negative response as final. Adhering to proper DNS settings and best practices is crucial to Active Directory processes, such as replication. DNS server configuration DNS is fairly simple and straightforward. As long as you follow the basic rules of configuration, DNS will give you few problems. However, there are certain complex configurations that are important to know about and remember when configuring DNS
servers, which can allow administrators to get a better handle on options that can make a difference in DNS operation, logging and troubleshooting. One of the first things to figure out when learning DNS in Active Directory is knowing if a property is that of the DNS server or a zone. Both are exposed in the DNS Management snap-in tool. Here are a couple of ways to keep them straight: 1. Server properties are general properties that apply to the whole DNS environment, such as Forwarding, Name Servers, root hints and logging. 2. Zone properties are specific properties that vary with the zone, such as dynamic updates, zone type (AD, Standard Primary or Secondary) and replication type. DNS structure and design DNS architecture design is also very important. When designing the DNS structure, it is important to keep in mind certain principles and practices that will affect the overall name resolution performance in the network. DNS structures that are patched together or not well thought out will work, but they have pockets of failure that will affect Active Directory performance. That is why adherence to best practices in the DNS structure is extremely important in creating an efficient and productive Active Directory. One key to designing DNS involves the use of Active Directory integrated zones (ADI). An ADI zone is a writeable copy of a forward lookup zone that is hosted on a domain controller. This is a requirement since the DNS records are all held in Active Directory, thus the DNS server needs access to the AD. Since each DC hosts a writeable copy of the DNS zone, clients (workstations, servers and other DCs) can register their DNS records on a domain controller hosting an ADI primary zone -- usually the DC that authenticated them -- rather than search the network to find a single DNS server (primary) that will add the client's host and resource records. So how is a DNS structure using Active Directory integrated zones designed? ADI zones can only be hosted on DCs. However, many administrators want to put domain name servers in remote sites to provide better name-resolution performance and to decrease network traffic. That way, users don't have to go across the WAN to find a DNS server. However, an administrator may not want to put a DC in that location. Windows 2000 Server and Windows Server 2003 allow admins to put a standard secondary zone (read only) on a member server and use one of the ADI primary servers as the master. The rule is that an ADI primary zone can only exist on a DC, but admins can have a standard secondary of that zone on a member server. Thus, clients can connect to their local DNS server whether it is hosting the ADI primary or the secondary. When a client (DC, member server or workstation) tries to register, however, it can only register on a
DNS server hosting the ADI primary zone. If the client points to a server hosting a secondary, the client will simply receive a referral to one of the primaries to be registered. Protecting DNS DNS security is a major priority. Many of the functions and features of Active Directory use DNS to locate domain controllers, systems, services, clients, and other objects. It should be obvious that protecting DNS is almost as important as protecting Active Directory itself. Basically, if DNS fails, so does Active Directory. This, in turn, means that if DNS fails, an entire network may be disabled. Providing protection for DNS as a means to provide additional protection for AD DCs is an essential part of establishing a truly secure networking environment. Protecting your DNS servers will require a multi-pronged approach. First and foremost, establish the same secure design, implementation and deployment procedures for your DNS servers as I've recommended for your AD DCs. Next, consider implementing secured communications with DNS servers, monitor all network traffic, and re-evaluate the open ports on your firewall. By encrypting all communications between DNS servers and all DNS clients (which includes not just end user clients but also Active Directory DCs and member servers), it will minimize or eliminate the possibility of traffic interception and manipulation. One of the best ways to implement this is through IPSec, which is is a framework for a set of protocols for security at the network or packet processing layer of network communication.
Note: While the implementation of IPSec across all systems will likely cause a measurable decrease in the performance of network communications due to the overhead of encrypting and decrypting communications, many experts feel the increased security should more than compensate for the slight reduction in throughput.
It is also important to monitor all network traffic and re-evaluate the open ports on your firewall. By monitoring network traffic, admins should be able to determine when illegitimate or abnormal traffic patterns or content begin to enter their network. Even with all recommended precautions in place, however, there is still a possibility of a malicious person gaining access to a DNS server. If that happens, admins must rely upon internal DNS security precautions, which include:
Secure dynamic updates DNS resource record registration quotas Delegate DNS administration Use secured routing Maintain a split DNS namespace Disable recursion
Troubleshooting DNS DNS troubleshooting is an absolutely vital process in Active Directory. It is important to keep DNS healthy and to know how to repair it when it breaks.
Security and Active Directory Avoiding Active Directory security breaches The importance of protecting your Active Directory has already been touched on in reference to DNS security. However, that is just the tip of the iceberg when it comes to maintaining a secure environment. As far as Active Directory security best practices go, layered security is the best method to use when planning and designing a security solution. Layered security or defense in depth is the simple concept of placing your valued assets at the center of your environment and building or deploying multiple concentric circles or rings of protection around those assets. Thus, violations to confidentiality, integrity, or availability must overcome numerous security restrictions, precautions, and protections before being able to affect your assets. While Microsoft has increased the default security within Active Directory (especially if you have a Windows Server 2003 Active Directory installation), you still need to consider additional security settings after it is installed. Securing your domain controllers One of the first steps you should take involves developing a solid domain controller security policy. Protecting your domain controllers is at the core of protecting your Active Directory investment. Without your domain controllers you won't have your Active Directory network infrastructure. With exposed and unprotected domain controllers you also are at risk for attackers to enumerate shared folders and usernames, giving up valuable information that can be used to further attack the network. Therefore, it is critical that domain controllers are running and protected in order for the Active Directory environment to remain functioning and stable. To protect domain controllers, you should consider the following areas of security protection: physical access (keeping DCs in a secure location that is only accessible by the IT staff) and network access (protecting DCs from those who might attack your network). As an administrator, you need to be concerned with making sure internal users have proper access and that potential intruders are frustrated in their attempts to
compromise a DC. One danger is for a person to be physically in the room and touch a DC even without any rights granted to them. Thus, if a person has physical access, he or she owns your computer, since physical access grants them control. Keeping DCs in a secure location is a simple way to ensure Active Direcotry security, but it is often overlooked. As far as network access is concerned, it is important not to give domain admin privileges to someone who isn't skilled enough to handle the job or to someone you're not sure you can trust. Anyone with the ability to install/modify system files, including services/drivers (such as server operators, backup operators or print operators) owns your computer. There are many ways for this to happen. Naturally, a secure account could be compromised, giving the intruder the rights to do this, but a valid holder of these rights could cause harm unintentionally by installing an application without testing it first. How well you handle Microsoft patch emergencies and updates is also key to the security of your DCs. You should always deploy the same patches on all domain controllers. DCs should be kept as close to mirror images of each other as possible, at least in terms of the OS configuration. This will help eliminate incompatibilities, lost or corrupted data and replication errors. However, it is important not to patch just because Microsoft offers a patch. Every patch needs to be tested in your environment for relevance and reliability. If you don't need it, don't install it. Patches can damage your environment if the install fails to perform perfectly. You don't want to place your DCs at risk if you can avoid it. Kerberos security with Microsoft With the inception of Windows 2000, Microsoft adopted Kerberos as an authentication protocol. Not only was it much more secure and efficient than NTLM (which was used prior), but it also plays nicely with other operating systems such as Unix. Before learning how Kerberos works in the world of Windows, it's best to first understand normal Kerberos authentication and authorization.
Authentication is the process of presenting credentials (username/password) to a
service and having that service validate you. It works like this. When a user enters his or her username/password in a Kerberos environment, that information is sent to a server running the Authentication Service. The Authentication Service passes that information to a database called the Key Distribution Center (KDC). If the username/password checks out, the Authentication Service sends a Ticket Granting Ticket (TGT) to the client, allowing the client to complete the logon process. The TGT contains a time stamp, the public key and a certificate.
Authorization is the process of granting access to resources on a server that is in the network. Continuing from the authentication discussion, once the client gets the TGT, the client can then request access to resources. The TGT is presented to the Ticket Granting Service and requests a session ticket to access a resource on, say, Server 1. If Server 1 is in the domain, the Ticket Granting Service sees that there is a valid TGT, so credentials check out, and a session ticket is granted for Server 1. The client then presents the session ticket to Server 1 for access to a resource such as a printer, file share or document. Server 1 will then check access rights on that resource to see what the user can do (read, write, etc.). In a Windows domain, all of the Kerberos-related services just described are held by each domain controller. When a user presents credentials for authentication in a Windows domain, the same Kerberos authentication process described above is used -with one exception. In order to find a domain controller that is also the KDC, a client must use the DC Locator process, which requires a DNS server to locate an appropriate DC and send that information back to the client. The client then passes the credentials to the domain controller, which grants the TGT and then a session ticket if the server to be accessed is in the DC's domain. The access rights are checked by the server and granted to the client. Group Policy security settings One of the most important steps toward Active Directory security involves Group Policy security settings. With almost 1,800 policy settings in a single Group Policy Object (GPO), it is no wonder they provide so much power, control, security, and management over an Active Directory enterprise. There are two default GPOs in every Active Directory domain. These default GPOs are there for very distinct reasons and should be investigated to ensure they are configured properly to provide the best security for your company network. The first default GPO is the Default Domain Policy. This GPO is responsible for establishing and maintaining the account policies for the domain user accounts, which are essential for helping secure the domain user account passwords. The second default GPO is the Default Domain Controller Policy. This GPO is responsible for establishing the baseline security for all domain controllers in the domain. The primary security settings that are established in the GPO are the user rights. Common user rights include:
Allowing a user to logon using the keyboard attached to the computer (locally) Changing the system time Backing up files and folders Accessing the computer and its resources over a network
However, every network running Active Directory should have more than just the default two GPOs. The reason is that Group Policy provides an automated, centralized method for configuring and deploying security settings to all computers and users within the domain. Some common security related settings and areas of configuration include the ability to restrict which applications can be run on each computer, use IP Security to encrypt data between computers, restrict anonymous connections to computers and audit policy settings per computer. Remember that there are several network security attacks that can be easily avoided with Group Policy, including simple steps for Kerberos configuration, so be sure to take advantage.
Active Directory planning and design It's important to know how to design a plan to implement Active Directory. You should always fully document your intended domains, forests, organizational units, sites, DNS infrastructure and security strategies. This documentation becomes the plan for your new infrastructure when you make the migration. The basics of Active Directory planning When you are performing an Active Directory migration, you basically have two options: domain upgrading or domain restructuring. Domain upgrading is little more than upgrading each existing Windows domain controller to a more current Windows domain controller. The upgrade process starts by upgrading the PDCs in each domain, followed by the BDCs. Domain restructuring involves creating an Active Directory network from scratch. In a restructure, you will move systems and reroute connections to comply with a new infrastructure and layout design. Often restructuring will result in fewer but larger domains. So the question becomes, "Should you upgrade or restructure?" Deciding which path to take, or which process to perform first, all depends on your specific situation. But there are a few guidelines that can help you make the choice. First, if your current domain structure is supporting your work tasks and doesn't seem to involve an inordinate amount of extraneous administration, then upgrading may be preferable. However, if the current domain structure is not adequate and is the primary motivation for the migration, restructuring is likely the way to go. Secondly, if you must support the production environment throughout the migration process, upgrading will retain overall network functionality and therefore is preferable. But if you can afford to lose productivity during the migration, restructuring is better. However, restructuring
can be performed on a staggered schedule so no significant loss of productivity is noticed. Rememeber that while upgrading will cause the least downtime in terms of getting the domain back into working order, it often is an insufficient migration. Many of the benefits of Windows 2000 and Windows 2003-based Active Directory domains cannot be fully realized without reconfiguring the design of your network. Restructuring will require significant work to implement, but it makes reaping the benefits of Active Directory easier to exploit for your organization. Developing an Active Directory migration strategy When taking on an Active Directory migration project, like with all large projects, it's best to have a strategy in place. It is key to create an Active Directory migration checklist, with steps such as collecting diagrams and configuration of the current DNS and network structure (bandwidth, remote locations, stability, etc.), determining the rights, objects and policies that will need to be migrated, and creating fall back procedures in case of failure. Another part of developing your migration strategy, is being aware of the key things you should and should not do when performing an Active Directory migration. For starters , it's important to make sure that your support staff is brought up to speed before you begin migrating any production system. Depending on the size and structure of your organization, you should have a help desk staff taking support calls. For a complex project like Active Directory, it's a good idea to make a couple of network engineers available as well. Be sure to train all members of the support staff involved in the process. Otherwise, you'll have IT staff fielding questions that they don't know how to answer, and frustration will abound on all sides. You should also establish a test bed that mimics your production environment as closely as possible in terms of hardware specifications and network speed. Leave nothing to chance in the testing phase. Speaking of testing, be sure to test name resolution and replication before deploying Active Directory in production. Unlike replication under NT4, Active Directory replication is possibly the single most important item required for AD to function correctly. Second only to file replication for a solid Active Directory implementation is name resolution. Whether you are deploying WINS or DNS, ensure that all systems that need to can effectively talk to one another. Designing Active Directory simply Active Directory is very flexible. So flexible that you can design an Active Directory forest that is complex beyond imagination. Both Windows 2000 Server and Windows Server 2003 support the Active Directory containers of forest, domain, site, and
organizational unit (OU). With the only real restriction of one forest per namespace, you can deploy as many domains, sites, and OUs as you deem necessary. However, don't be so fast to rush off and design an Active Directory network that includes a domain for every department in your enterprise. The key to Active Directory design is simplicity. As a general rule, you want to keep the number of domains to a minimum whenever possible. If you really need department level divisions on your network that reflect the organization of your business, then use OUs instead. OUs are much more flexible and easier overall to manage than domains. If you are migrating from a Windows NT 4.0 network to a Windows 2000 Server or Windows Server 2003 Active Directory network, compare the number of domains from your existing legacy system and compare that with the number of domains in your new AD-based design. If your new Active Directory network has more domains than your legacy network, you may need to re-think your design. Yes, it is possible to use as many domains as you wish, but you'll likely regret that decision down the line. If you need lots of groupings and divisions, it is best to rely upon OUs. Active Directory domain design When you are designing your Active Directory network, it is important to use the four divisions (forests, domains, organizational units, and sites) to their maximum potential. This is especially true for Active Directory domain design. Domain divisions are most often used as logical containers. However, Microsoft recommends that you employ domains also as physical containers. In other words, create domains whose members are all geographically close rather than distant. This is an important design aspect since the level of traffic within a domain is considerably higher than that between one domain and another. In general, a domain with limited physical size is less likely to include expensive WAN links or pay-per-bit connections. When slow links must be included in a network design, it is often beneficial to create multiple domains connected by the slower connections. Remember that it is not necessary to create separate domains to divide administrative privileges. Within Active Directory, it is possible to delegate administrative privileges based on organizational units. Designing groups and organizational units With the proper preparation and advance knowledge of their use, a functional organizational unit (OU) and group design can do wonders to simplify your Active Directory environment. It can also go a long way toward helping you gain control and reduce overhead.
Often, OUs are indiscriminately used without reason, and group structure is ineffectual and confusing. Without some form of logical organization of users within your network environment, chaos reigns and administration grinds to a halt. Some best practices when designing OUs include:
Keep the OU structure as simple as possible Do not nest OUs more than 10 layers deep Keep the number of OUs to a minimum Apply Group Policy to groups through Group Policy filtering Don't utilize local groups for permissions in a domain environment Use domain local groups to control access to resources, and use global groups to organize similar groups of users.
You also have the option of hiding your OUs. The primary purpose of hidden OUs is to prevent an administrator from one OU from being able to view, access, or alter another OU. Hidden OUs are often used in environments that offer network application services to internal departments or external customers. It allows for a solid separation of duties without requiring separate domains or forests. Design rules for Active Directory sites Sites are an extremely useful design element for Active Directory domains. Sites are limited to any computer object within a forest. Thus, they can cross domains and organizational units (OUs) with indifference. An object's membership in a domain or OU does not exclude simultaneous membership in a site. Sites are used to impose physical network divisions for the purpose of traffic flow. By using sites, you can control and reduce the amount of traffic that flows over your slower WAN links. This can result in more efficient traffic flow for productivity tasks. It can also serve to keep WAN link costs down on the pay-by-the-bit services. In general, when designing sites, keep the following in mind:
Sites should generally reflect the physical or geographic topology of the network. Each site should contain at least one local DC. Sites should not contain slow links of any type. Remote-access clients do not need a dedicated site. Sites should be used whenever control over replication traffic is needed or desired. Sites can be added, removed, changed, and moved easily without affecting any other AD container configuration.
Changes to Active Directory Microsoft has made many changes and improvements to Active Directory since its first incarnation for Windows 2000 Server. It is important for IT managers and administrators to understand the differences in Active Directory in regards to which version of Windows they are using. Differences in Active Directory for Windows 2000 and Windows 2003 For the new features and improvements that were built into Windows Server 2003's Active Directory, Microsoft focused on five areas: 1. 2. 3. 4. 5. Integration and productivity Performance and scalability Administration and configuration management Group Policy Security
Some changes in the areas of integration and productivity include the abilities to edit multiple Active Directory objects simultaneously, as well as improved interoperability via inetOrgPerson for Novell and Netscape solutions. Replication monitoring was also improved for Windows Server 2003. In particular, a replication enhancement called linked-value replication for objects such as Active Directory group objects was significant, especially for large environments. Linked-value replication solved problems such as inconsistent replication and delays by replicating multi-valued attributes separately. As far as performance and scalability goes, Microsoft eliminated the need to contact a global catalog (GC) server each time a user logs in. For Windows Server 2003, the GC information is cached at the local domain controller. Other enhancements include support for clustered virtual servers, DC overload prevention and GC replication tuning controls. For better configuration management, Microsoft added automated DNS zone creation, improved inter-site replication and the ability to rename domains. Better migration and command-line tools were also created for Windows Server 2003 Active Directory. Some of the new command-line tools include:
dsadd -- Allows you to create objects from the command line dsmove -- Moves an object from one OU or container to another within
the same domain dsrm -- Will delete an object from Active Directory dsquery -- Will return an object or list of objects that matches criteria that you specify
dsget -- Will return one or more attributes of a particular Active Directory
As for Group Policy, Windows Server 2003 greatly improved the Group Policy management interface, which is able to interact with both 2003 and 2000 GPOs. Other improvements included GPO results reports, over 150 new GPO controls and improved client management features. New security features included forest trusts, trusted namespaces, cross-forest authentication and authorization, and a credential manager. Other changes to Active Directory for Windows Server 2003 include the "Install from Media" option for promoting new domain controllers into a domain, and the Users and Computers MMC snap-in which allows admins to move an object from one location in the directory tree to another more easily. Active Directory improvements with Windows Server 2003 SP1 Several changes in Windows Server 2003 Service Pack 1 have to do with the way Active Directory handles "tombstoned" objects. Just like in Windows 2000, when you delete an Active Directory object, it is not immediately deleted; instead, it's marked as a tombstoned object. This allows the deletion to be replicated properly to other domain controllers. Once an object has been in this tombstoned state for a certain amount of time, it is finally deleted outright. In Windows 2000, the default tombstone lifetime was 60 days. However, in Windows Server 2003, Microsoft changed it to 180 days, effectively tripling the amount of time that a deletion had to be communicated to all of the domain controllers in an environment. However, if you have already installed Active Directory using either Windows 2000 or the original Windows Server 2003 media, the default tombstone lifetime will not automatically change when you upgrade to Windows Server 2003 SP1. You will only receive the 180-day tombstone lifetime value automatically by building a pristine 2003 SP1 Active Directory forest. In addition to modifying the tombstone lifetime for new Active Directory installations, 2003 Service Pack 1 added the SID History attribute to the list of attributes that are retained when an object is tombstoned. When an Active Directory object is tombstoned, it is stripped of most of its attributes, so the tombstoned object only takes up a fraction of the size of the original object within the Active Directory database. Each user, group and computer object within Active Directory is assigned a numeric security identifier, or SID. SIDs are unique within the domain and do not change, even if the security principal is renamed or moved to another container within the same domain. Prior to Windows Server 2003 SP1, one of the attributes that was stripped when an object was tombstoned was this SID History attribute, which meant that if you restored an object, any previous SIDs that were recorded in its SID History were lost.
Fortunately, Windows Server 2003 SP1 includes SID History among the attributes retained when an object is deleted. Service Pack 1 also made changes in the types of Active Directory information that are logged in the Event Viewer on a domain controller, thus allowing for more proactive monitoring and easier troubleshooting. One such update is Event ID 2089, which is recorded in the Directory Service event log if any directory partition has not been backed up for a significant length of time (half of the tombstone lifetime or more). The event is logged whether the partition is the Schema, Configuration, or domain partitions -- or any application partitions or ADAM partitions that are hosted on the DC in question. Ever since SP1, administrators can also now run domain controllers using virtualization technology such as Microsoft Virtual Server 2005. That allows you to run multiple domains or forests on a single machine or to use virtualization to reduce the attack footprint of a physical server by separating its roles onto multiple virtual machines. Changes to Active Directory for Windows Server 2008 Once again, many changes to Active Directory were made with Windows Server 2008. Microsoft has incorporated two very significant features with Windows Server 2008 that will probably relate to most Active Directory deployments: the read-only domain controller (RODC) and server roles. The read-only domain controller is perhaps the marquee feature for Active Directory in Windows Server 2008. The RODC hosts a read-only copy of the Active Directory database. That is, you can't make any changes to the Active Directory database from a read-only domain controller. You can connect to an RODC to read any information you like (with a few exceptions, which we'll get to in a moment), but you will not be able to perform any write operations without connecting to or being referred to a writeable domain controller. Also with RODC, the administrator can determine which accounts will be replicated to the domain controller, and replication is unidirectional. RODC does not perform any outbound replication. This is a fundamental change from the typical multi-master replication model that many have become familiar with in Active Directory. In Windows 2000 Server and Windows Server 2003, an administrator can connect to any domain controller to make a change, and that change will be replicated out to the rest of Active Directory via outbound replication from the DC that the change originated from. This is not so with the RODC. The read-only domain controller will receive inbound replication from other writeable Windows Server 2008 DCs, but it will not replicate any information whatsoever out to other DCs. This solves a lot of security issues at remote sites since it will minimize accounts exposed at the site (presumably not any admin
accounts), and anything compromised at the site will not make it out of the site. Combined with the new BitLocker technology, RODC will allow deployment of DCs at smaller sites where it was not feasible before. Server Core was also developed for Windows Server 2008 as a response to customer requests to provide a lean server operating system that would permit specific server functions to run without all the overhead of the GUI. It has been referred to by Microsoft as a bare bones installation of Windows Server 2008. With Server Core, after logon, a user will be presented with a desktop with no start menu, taskbar or icons, and two command windows. Installation of roles such as Dynamic Host Configuration Protocol (DHCP), DNS, file services and print server will be done completely from the command line. However, this environment will still allow users to open applications such as Event Viewer, notepad and others. In addition to making the server better defined for administrative purposes and reducing the hardware resources required, Server Core also permits better security at remote sites, allowing a smaller footprint of exposure. Other changes include the Restartable Active Directory, which allows AD to be restarted without rebooting the server. You can accomplish this via the command line and MMC Snap-ins. It is designed to save admins time on offline operations (like an offline defrag of Active Directory) without taking the server offline and shutting down other services and applications. Active Directory in Windows Server 2008 R2 Microsoft built on Windows Server 2008 with the release of R2, which featured two notable Active Directory changes. First, the company unveiled the new Active Directory Administrative Center (ADAC) for managing directory service objects, somewhat replacing the usual AD Users and Computers snap-in from past releases. One caveat of the ADAC is that it can only be used on machines running Windows Server 2008 R2; all previous versions of Windows still require AD Users and Computers. It can, however, be used to manage Windows 2003 and 2008 domains. It should also be noted that the old Users and Computers snap-in is still available with R2, so admins can continue to use it while learning the ins and outs of ADAC. The second most notable update to Windows Server 2008 R2 Active Directory is the addition of the AD Recycle Bin. The tool is designed to work similar to the familiar Windows Recycle Bin to make it easier for admins to recover accidentally deleted objects. Though initially met with enthusiasm from IT pros, some were initially disappointed with the Active Directory Recycle Bin, citing that while it was a step in the right direction, the utility still lacked functionality found in more mature, third-party recovery tools.
Other Active Directory changes with Windows 2008 R2 include a Best Practices Analyzer, a flurry of new PowerShell cmdlets and added offline domain join functionality. Microsoft also introduced a new managed service accounts feature designed to improve security for application management. The company has announced plans to improve the feature with the first service pack for R2 for app servers and services running in perimeter networks. Windows Server 2008 R2 SP1 will also feature enhancements for domain controller scalability.