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Planning a Strategy for Placing Global Catalog Servers

A Global Catalog (GC) contains location information for every object created, whether it was created by default upon installation or manually with the AD. It is also responsible for several other important features, such as the following:

  • Logon validation of universal group membership

  • User principal name logon validation through DC location

  • Search capabilities for every object within an entire forest


The GC retains only frequently searched for attributes of an object. There is no need, nor would it be very practical from a replication standpoint, for the GC to retain every single detail of every single object. Then the GC would be, in fact, no different from a regular DC. Instead, the GC is a DC that performs this additional functionality.

Several factors need to be considered with regard to the GC and how it functions to enhance logon validation under a Windows 2000 native mode or Windows Server 2003 functional level situation.

GC and Logon Validation

Universal groups (discussed in Chapter 4) are centrally located within the GC. The universal groups a user belongs to are quite important in the creation of an access token, which is attached to that user and is needed to access any object, to run any application, and to use system resources. The access token is what literally holds the SID and the group IDs, which indicate what groups the user belongs to. Those access tokens are necessary for logon validation as well as resource access, so each token must include a user's universal group membership.

When a user logs on to a Windows 2000 native mode or Windows Server 2003 functional level domain (these are the only ones to include universal groups), the GC updates the DC as to the universal group information for that particular user's access token. But what if a GC is unavailable for some reason? Then the DC will use "cached credentials" to log the user on to the local computer. This cached logon provides the same level of access to network resources as the user had the last time they logged in. Furthermore, those credentials would exist only if the user had logged on prior to this point. What if the user had never logged on and the GC is not available for the first logon? If no GC server could be contacted either locally or at another site, the user would not be able to log on to the domain and could either log on locally to the machine itself or wait for a GC to become available again.

Evaluating Network Traffic Considerations When Placing Global Catalog Servers

Because GC servers are prominent in logon validation and in locating AD resources, it is important to plan for their placement on a complex LAN. Ideally you would have at least one GC server at each AD site, though this isn't always practical, especially for small branch offices. GC traffic increases the burden on WAN links, so there is a tradeoff between having remote sites needing to contact a GC across a WAN link versus the additional replication traffic that a GC server will generate across the WAN link. Microsoft recommends having a GC server at each site, though, if your server hardware will support it.

Evaluating the Need to Enable Universal Group Membership Caching

With the Windows 2000 native mode, a GC server must be available at all times to verify universal group membership. If you have sites separated by slow or unreliable WAN links, the practice is to place a GC server at each local site. The downside to this is that replication traffic is increased. If the domain is operating at the Windows Server 2003 functional level, you can enable the caching of universal group membership so users can log in even if no GC server is available.

Universal Group Membership Caching is most practical for smaller branch offices with lower-end servers, where it might be problematic to add the additional load of hosting a GC, or locations that have slower WAN connections. To enable caching, use the Active Directory Sites and Services utility. Navigate down the left side of the console and click the site at which you want to enable caching. On the right side (the contents pane), you'll see NTDS Site Settings, as shown in Figure 3.6. Right-click this and choose Properties, which brings up the dialog box shown in Figure 3.7.

Figure 3.6Figure 3.6 Configuring Universal Group Membership Caching through NTDS Site Settings in Active Directory Sites and Services.

Figure 3.7Figure 3.7 Check the box to enable Universal Group Membership Caching and select a cache server if desired.

To enable Universal Group Membership Caching, simply check the box on the property sheet. You have the option of choosing a specific server to refresh the cache from or leaving it as default, which will cause Windows Server 2003 to attempt to refresh the cache from the nearest GC server it can contact. By default, Windows Server 2003 will attempt to refresh the cache every 8 hours.

Once caching has been enabled, a user must log in once for his information to be cached. Upon the initial logon, a GC server must be contacted to obtain the group membership information, but after the initial logon the information is cached. As a result, logon times are faster because a GC server doesn't need to be contacted, and network bandwidth utilization is improved without GC replication taking place.


Pay keen attention to the functionality of a GC. Your knowledge of GCs will enable you to determine whether possible solutions will resolve defined problems.

User Principal Names and Logon Validation

Normally, an individual might log on to a domain with her common name and password. For example, suppose the user's common name is DonnaD and her password is Duncan1968. Now suppose Donna attempts to log on to the system using her principal name—for example, donna@virtual-realm.com. If Donna is attempting to log on from a system that is in the accounting domain, the DC in acct.virtual-realm.com will not know her account. However, the DC will check with the GC, and that will, in turn, lead to the DC for the virtual-realm.com domain. The user will then be validated.

Adding GC Servers

Not all DCs are GC servers. Following are several thoughts to keep in mind:

  • The first DC in a forest is a GC server.

  • Any DC can be a GC server if set up to assume that function by the system administrator.

  • Usually one GC is helpful in each site.

  • You can create additional GCs if necessary.

To add another GC, perform the following tasks from AD Sites and Services:

  1. Within the tree structure in the left pane, expand the DC that will be the new GC.

  2. Right-click NTDS Settings and select Properties.

  3. In the NTDS Settings Properties dialog box, under the General Tab, select the Global Catalog check box, as shown in Figure 3.8.

Figure 3.8Figure 3.8 Adding a Global Catalog server. Exam Prep Questions

Question 1

There are five operations master roles on a Windows Server 2003 network. Where is the data regarding which servers are playing which roles stored?

  1. It is stored in the Registry of the server performing the role.

  2. It is stored within Active Directory.

  3. It is stored in the Registry of the clients.

  4. It is stored in a database separate from Active Directory.

Answer B is correct. This data must be in Active Directory so clients and down-level servers can query the database when an operations master is required. Answers A and C wouldn't be effective because the Registry is used only by a local machine, and if the data is stored locally, other machines on the network won't be able to access it. Answer D is incorrect because Windows Server 2003 uses no other database than Active Directory.

Question 2

Which of the following are names of the operations master roles? [Check all correct answers.]

  1. Schema Master

  2. Infrastructure Master

  3. SID Master

  4. Domain Naming Master

Answers A, B, and D are correct. The operations master roles that are missing are RID Master and PDC Emulator. Answer C is incorrect because there is no such role as the SID Master. The SID is the common domain portion that identifies a client's membership, and with the RID (relative identifier) it uniquely identifies an AD object such as a user account.

Question 3

James Pyles is attempting to create a universal group in a child domain, but the option is unavailable. There are several child domains under a single parent domain that all have the ability to create universal groups, with the exception of this one. What would be a valid reason for James having such a dilemma?

  1. The domain is still residing in Windows 2000 mixed mode.

  2. The domain is not running at the Windows Server 2003 functional level.

  3. The domain is still in Windows 2000 native mode and needs its functional level raised.

  4. James is attempting to create the group on a backup domain controller (BDC).

Answer A is correct. If James is still residing in a Windows 2000 mixed-mode scenario, his groups will be only domain local and global. Universal groups exist only in Windows 2000 native mode and at the Windows Server 2003 functional level. It is perfectly legitimate for one domain in a tree to be at the default Windows 2000 mixed mode while other child domains in the tree have had their functional levels raised. Answer B is incorrect because universal groups are also available at the Windows 2000 native mode functional level. Answer C is incorrect because Windows 2000 native mode supports universal groups, so James would not need to raise the functional level. Answer D is incorrect because domains in Windows Server 2003 do not use BDCs, nor would it matter which DC James tried to implement a security group on if the domain is not in native mode.

Question 4

Ayman Mohareb ("Mo") is a system administrator for a large company. Mo has noticed that he is getting a lot of errors in the system log of Event Viewer. The errors relate to time synchronization on his network. Mo knows that this is related to an operations master role. Which role performs time-synchronization duties?

  1. The Infrastructure Master

  2. The Schema Master

  3. The Domain Naming Master

  4. The PDC Emulator

Answer D is correct. The PDC Emulator performs time-synchronization duties within its domain. It, in turn, synchronizes with the PDC Emulator in the root domain. The PDC Emulator in the root domain should be synchronized with an external source. Answer A is incorrect because the Infrastructure Master is responsible for updating cross-domain references of objects. Answer B is incorrect because the Schema Master role is to operate as the single location where changes to the schema can be made. Answer C is incorrect because the Domain Naming Master is used to add or remove domains from the forest.

Question 5

Robyn Hitchcock is a member of the Domain Admins group in a Windows Server 2003 network. He has been asked to add a new object type to AD. However, whenever he tries to access the schema, he is denied access. A new Windows Server 2003 MCSE named Jaime Rodriguez says this is because of insufficient permissions. However, because Robyn is a member of the Domain Admins group, Robyn doubts this is true. Instead, Robyn thinks it is a network problem. Who is right?

  1. Jaime is right. Domain Admins do not have sufficient permissions to make changes to the Active Directory schema. One must be at least a Schema Admin to do this.

  2. Robyn is right. Domain Admins have all permissions on a Windows Server 2003 network; therefore, he should be able to change the schema.

  3. Neither is correct. Domain Admins can change a schema; therefore, Jaime is incorrect. However, receiving an "access denied message" indicates a server problem, not a network problem.

  4. Jaime is right. Domain Admins do not have sufficient permissions to make changes to the Active Directory schema. One must be at least an Enterprise Admin to do this.

Answer A is correct. Only members of the Schema Admins group can make changes to the schema. Therefore, answers B, C, and D are all incorrect.

Question 6

Pete Umlandt is attempting to log on to a domain called research.corp.com, although his user account is located in corp.com. Pete is using his user principal name, pete@corp.com. What feature of an Active Directory network will most assist him in logging on to the system?

  1. Universal groups

  2. Global Catalog servers

  3. Additional domain controllers

  4. Kerberos authentication

Answer B is correct. Global Catalog servers search for the domain information necessary during logon when an individual uses his user principal name. Answer A is incorrect because although universal groups can ease administration in domains that have had their functional levels raised, they won't help with logging in through a child domain. Answer C is incorrect because although additional domain controllers will add fault tolerance, they are not necessarily GC servers and will not assist in logon validation. Answer D is incorrect because although Kerberos is used to verify authentication to the resources, it doesn't assist in the location of the GC domain controller that will validate a user.

Question 7

The Domain Naming Master server has crashed. The word from the hardware techs onsite is that it will take a week to order the parts to get it back up and running. Matt Thomson is the system administrator, and this could not have happened at a worse time. Matt was due to work all weekend creating two new domains. He knows that not having a functioning Domain Naming Master will prevent him from creating new domains. Therefore, Matt decides to seize the role of Domain Naming Master. Which tool will he use to perform this task?

  1. Matt will use the Ntdsutil command-line utility.

  2. Matt will use Active Directory Domains and Trusts to seize the role, because this is a forestwide operations master.

  3. Matt will use the Active Directory Users and Computers tool. This tool is used to seize all roles except that of the Schema Master.

  4. Matt will deactivate the current Domain Naming Master with Ntdsutil. He will then use Active Directory Domains and Trusts to assign the role to another server.

Answer A is correct. There is no need to use two tools to perform this task. Matt simply needs to use Ntdsutil, a command-line utility with many different options, to seize the role. Answer B is incorrect because Active Directory Domains and Trusts is not used to seize roles. Answer C is incorrect because one cannot use Active Directory Users and Computers to seize forestwide roles. Answer D is incorrect because Active Directory Domains and Trusts is not used to seize roles.

Question 8

Marty Bouillon has just been added to the Schema Admins group, so he can make some additions to the schema of Active Directory. Marty knows that this task is very important and that he must be careful when editing the schema. Fortunately, his development background has prepared him for the task. Marty knows that he must create a custom MMC in order to edit the schema using the Schema MMC snap-in. However, when he tries to add the snap-in, it is not available on his system. He calls his help desk and asks to be added to all the necessary groups to enable this function, but the help desk tells him that it is not a permissions issue. What must Marty do to fix this problem?

  1. Marty must contact the help desk manager because the help desk is incorrect; this is a permissions issue. One must be both a member of Schema Admins and Enterprise Admins to edit the schema.

  2. Marty is obviously using a Windows 98 computer. The MMC does not work on a Windows 98 box. Marty must upgrade his system to Windows 2000 or XP.

  3. Marty must first register schmmgmt with the regsvr32 command. He will not be able to use the Schema MMC snap-in until this is done.

  4. Marty should call the help desk and ask its staff to seize the role of Schema Master. The snap-in not showing on the system is indicative of the server being unavailable.

Answers C is correct. Marty cannot use the Schema MMC snap-in until he registers schmmgmt with the regsvr32 command. Answer A is incorrect because the help desk was correct; this is not a permissions issue. Answer B is incorrect because the MMC does work on a Windows 98 box. Answer D is incorrect because Marty would not know that the Schema Master is not available until he tried to make a change to the schema. Because he cannot even find the snap-in, this is not the case.

Question 9

Miriam Haber is performing a review of the installation plan for her new Windows Server 2003 network. Her staff has detailed the placement of all DCs and operations masters. The administrators are in a small building on a single subnet. There are 10 administrators. The network design team proposes that two DCs be placed in its site. Because there are only 10 people, one server would be fairly slow. A more powerful server would be a Global Catalog server and the Infrastructure Master. Miriam rejects this plan and asks the network design team to reconsider. What was it about this design that she did not like?

  1. Although two DCs are reasonable in other circumstances, the role of the administrators is too important not to have at least three.

  2. The Infrastructure Master will not operate on a server that is functioning as a Global Catalog server. Either one of these tasks should be moved to the second DC.

  3. The Infrastructure Master role does not need to be close to the administrators. Because this role is used only for schema updates, it would be better to move this elsewhere and to replace the role with something more pertinent to the administrators' jobs.

  4. Miriam wants the help desk team to be moved to another site. Having it in a separate site will cause performance issues.

Answer B is correct. Although some of the other answers sound good, only answer B has it right. Two DCs should give enough redundancy, but three would not be going overboard either. However, answer A is incorrect because not having three would not cause the plan to be rejected. Answer C is incorrect because there are other roles that could be close to the administrators, too, but depending on what type of tasks are performed most commonly, it might make sense to make the Infrastructure Master closest. Answer D is incorrect because although the administrators are in a different site, that does not necessarily mean they have a slow connection to the rest of the network. Sites are also sometimes used to manage replication. Regardless of any of this, the Infrastructure Master will not operate correctly on a server that is also a Global Catalog server.

Question 10

Sandy Garrity is the design analyst who determines the AD structure for W&W, Inc. The structure takes into account the physical distribution of the company, with its headquarters in Lewisville, TX and three branch offices located in Omaha, Seoul, and Barcelona. She determines a need to create a headquarters domain root called w-w.com with three child domains beneath. By default, how many Global Catalog servers will there be for this widely dispersed solution?

  1. One

  2. Three

  3. Four

  4. Zero

Answer A is correct. The first DC for the entire forest will contain the role of Global Catalog. By default, this is the only GC in the entire forest. It is recommended that the administrator manually create additional GCs in remote locations and do so at a time when it will be the most convenient for network traffic between the GCs. GCs hold a copy of every object in the entire forest and a subset of attributes for each of those objects. Answers B and C are incorrect because they provide for too many. Answer D is also incorrect because there is always at least one GC for the forest.

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