n case you aren’t familiar with Global Catalog Servers, they are simply domain controllers that have been designated to perform the Global Catalog server role. When you create an Active Directory forest, the first domain controller in the forest is automatically assigned the Global Catalog server roll, because every forest requires at least one Global Catalog server.

The Global Catalog server performs a variety of tasks, both for Windows and for Exchange. Since my primary focus in this article is Exchange Server, I don’t really want to get into the Global Catalog server’s Windows related function. I will tell you though, that if a Global Catalog server is not available, then nobody will be able to log into the domain except for the Administrator.

As you can see, the Global Catalog server performs some critical functions at the Active Directory level, but its role in relation to Exchange Server is just as critical. In order for clients to be able to send and receive mail, both the Outlook client and the Exchange Server must be able to query a global catalog server. Without access to a Global Catalog server, Outlook clients will not be able to open the Global Address List or resolve the e-mail addresses of message recipients within the forest.

Global Catalog Server Placement

Now that I have given you an idea of why Global Catalog servers are so important, let’s talk about placement. Given the fact that any domain controller that’s running Windows 2000 or Windows Server 2003 can be designated to act as a Global Catalog server, it might be tempting to just designate every domain controller to act as a Global Catalog server. In most cases this is a bad idea though. Global Catalog servers produce quite a bit of traffic related to the replication process.

Over the years, Microsoft has released several different guidelines for Global Catalog placement, many of which are contradictory. One set of guidelines states that you should place a Global Catalog Server into any site that contains a server that’s running an application that makes use of port 3268 (the Global Catalog lookup port). Exchange Server is such an application, so if you were to follow this rule, then you would want to place a Global Catalog server into any site that contains an Exchange Server.

Another Microsoft document that I read suggested placing a Global Catalog server into each site, regardless of what the site is used for. I tend to think that this is the best approach, given the critical nature of Global Catalog servers, and the fact that clients make use of the global catalog during the logon process. Microsoft does state however, that a site doesn’t need a Global Catalog server if the site does not contain any servers running Global Catalog dependant applications (such as Exchange), contains fewer than 100 users, and is directly connected to a site that does contain a Global Catalog Server.

Keep in mind that this is a generic guideline though. The recommendations change depending on the size and topology of your network. For example, in large organizations with lots of Exchange mailboxes, it is possible for a Global Catalog server to become overwhelmed. To keep that from happening, Microsoft recommends having one Global Catalog Server for every four mailbox servers. Therefore, if a site contained eight mailbox servers, then you would want to place at least two global catalog servers in that site.

Of course not every network is large enough to have multiple sites. If you have a single site, single domain network, then it is safe to go ahead and designate all of your domain controllers to act as Global Catalog servers. In this type of environment, all of the domain controllers contain full copies of the Active Directory anyway, so the additional resource consumption caused by having multiple Global Catalog servers will be minimal.

Summary

Being that Global Catalog servers are so critically important to the Active Directory and to Exchange, it is important to make sure that your network uses them in an optimal manner. In this article, I have provided some general guidelines to Global Catalog server placement.

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Windows Server 2008 menawarkan banyak fitur baru, salah satunya adalah pada lingkungan Active Directory. Banyak improvisasi pada Active Directory di Windows Server 2008 dibandingkan di Windows Server 2003. Pada Windows Server 2008, ada 5 buah Active Directory, yang mana masing-masing bertindak sebagai sebuah Role.
Ke 5 Active Directory itu adalah :
- Active Directory Domain Services (ADDS)
- Active Directory Federation Services (ADFS)
- Active Directory Lightweight Directory Services (ADLDS)
- Active Directory Certificate Services (ADCS)
- Active Directory Rights Management Services (ADRMS)
Active Directory Domain Services (ADDS) adalah pengembangan dari Active Directory yang ada di Windows Server 2003. Pada Windows Server 2008, ADDS memiliki beberapa fitur baru seperti Granular Password, Read-Only Domain Controller, Improvement pada Auditing Services, Support untuk Server Core serta Restartable.
Active Directory Federation Services (ADFS) adalah role Windows Server 2008 yang digunakan untuk identity access. Artinya, ADFS ini memungkinkan trust antar domain (misal, company A berpartner dengan company B, maka mereka melakukan federasi antar domain mereka), dengan tujuan authentikasi antar domain bisa dilakukan dengan single sign on.
Active Directory Lightweight Directory Services (ADLDS) bertugas untuk akses directory services melalui LDAP. Role ini pada Windows Server 2003 disebut sebagai Active Directory Application Mode (ADAM). Fungsi yang ditawarkan sebenarnya mirip dengan ADDS, namun pada ADLDS, tidak wajib diperlukan sebuah Domain Controller.
Active Directory Certificate Services (ADCS) pada Windows Server 2003 adalah sebuah komponen Certificate Server. Pada Windows Server 2008, Certificate Services masuk pada jajaran Role Active Directory, namun masih dengan fungsi yang sama dengan Certificate Server pada Windows Server 2003.
Active Directory Rights Management Server (ADRMS). Pada Windows Server 2003, fitur ini bernama RMS (Rights Management Services). Dari segi fungsi, tetap sama, namun di WIndows Server 2008, fitur ini sudah menjadi 1 role. Fungsi dari RMS adalah untuk melakukan enkripsi terhadap dokumen Microsoft Office sehingga kita bisa mengatur permission terhadap dokumen tersebut dan user-user siapa saja yang bisa mengakses, serta pembatasan hak terhadap akses dokumen. User-user yang dimaksud adalah user-user yang ada di Active Directory, karena untuk mengakses dokumen yang terenkripsi oleh RMS tersebut, dibutuhkan authentikasi antara RMS client dengan RMS server (untuk request Public Key).
Raymond Engelbert