Thursday, November 12, 2009

How DNS and AD DS are Tied Together

When implementing Active Directory within your environment, DNS is required. Active Directory cannot exist without it. The two entities are like trains and railroad tracks. The train’s engines are mighty-powerful machines that can pull thousands of tons of equipment, but without the tracks, they cannot move. If the tracks are not aligned correctly, the train may derail. If the tracks are not switched in the right direction, the train will not arrive at the correct destination.

If you haven’t immersed yourself in the finer details of DNS, now is the time. If you think you understand how DNS works, you should still review all of the new options that have been added to the DNS service in Windows Server 2003 (including R2) and Windows Server 2008. Where Windows 2000 added some fancy new features into the Microsoft DNS world (such as support for dynamic updates and service locator [SRV] records), Windows Server 2003 upped the ante even more with support for stub zones and the ability to use application directory partitions for Active Directory–integrated zones.

As we mentioned previously, you are not required to use Microsoft’s implementation of DNS; UNIX BIND (Berkeley Internet Name Domain) DNS will work just fine as long as it meets certain criteria. As a matter of fact, several companies are already invested deeply in a BIND DNS solution and are not about to completely restructure with a new DNS implementation. As the old saying goes, don’t fix what isn’t broken. We will look at using BIND within your.

Looking at the correlation between your Active Directory and DNS, you will find the two share the same zone-naming conventions. If your Active Directory domain name is zygort.lcl, the DNS namespace will also be zygort.lcl. Notice that the top-level domain (TLD) name for DNS, in this case lcl, does not have an equivalent domain within Active Directory. That is because, for most companies, the top-level domain is not unique and is not owned by the company. Take for instance a company that is using as its Active Directory namespace. The TLD used in this case (com) is owned by the Internet Corporation for Assigned Names and Numbers (ICANN) and is shared by hundreds of thousands of Internet-based websites. When designing Active Directory, the designers decided to make sure that the root of the Active Directory forest could be unique; they required the domain names to take on two domain components: the company’s DNS domain and the TLD that it resides under.

As a domain controller comes online, part of its startup routine is to attempt registration of the SRV records that identify the services that are running on the domain controller. The only requirement for a DNS server to work with Active Directory is that the DNS server support SRV records. It does not matter to Active Directory clients if the records are entered manually by an administrator or automatically by the domain controller itself; all that matters is that the records are correct. If the SRV records are not listed within the zone or are entered incorrectly, the client will not be able to locate the domain controller. If the SRV records are correctly listed within the DNS zone, the host name of the server that is providing the service is returned to the client. The client will then query the DNS server for the A record (hostname record) of the domain controller to resolve the IP address.

Source of Information : Sybex Mastering Active Directory for Windows Server 2008

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