Monday, May 30, 2011

DNS in Windows Server 2008 R2

The Windows Server 2008 R2 improvements on the basic BIND version of DNS help to further establish DNS as a reliable, robust name-resolution strategy for Microsoft and non-Microsoft environments. An overall knowledge of the increased functionality and the structural changes will help you to further understand the capabilities of DNS in Windows Server 2008 R2.

Application Partition
Perhaps the most significant feature in Windows Server 2008 R2 DNS implementation, Active Directory-integrated zones are stored in the application partition of the AD. For every domain in a forest, a separate application partition is created and is used to store all records that exist in each AD-integrated zone. Because the application partition is not included as part of the global catalog, DNS entries are no longer included as part of global catalog replication.

With the application partition concept, replication loads are now reduced while important zone information is delegated to areas of the network where they are needed.

Automatic Creation of DNS Zones
The Configure a DNS Server Wizard, as demonstrated in 「Installing DNS Using the Add Roles Wizard」 section, allows for the automatic creation of a DNS zone through a step-bystep wizard. This feature greatly eases the process of creating a zone, especially for Active Directory. The wizard can be invoked by right-clicking on the server name in the DNS MMC and choosing Configure a DNS Server.

Fix to the 「Island」 Problem
Earlier versions of the Microsoft DNS had a well-documented issue that was known as the 「island」 problem, which was manifested by a DNS server that pointed to itself as a DNS server. If the IP address of that server changed, the DNS server updated its own entry in DNS, but then other DNS servers within the domain were unable to successfully retrieve updates from the original server because they were requesting from the old IP address. This effectively left the original DNS server in an 「island」 by itself, hence the term.

Microsoft DNS fixed this problem in Windows Server 2003 and above. Windows Server 2008 R2 DNS first changes its host records on a sufficient number of other authoritative servers within DNS so that the IP changes made will be successfully replicated, thus eliminating this 「island」 problem. As a result, it is no longer necessary to point a root DNS server to another DNS server for updates, as was previously recommended as a method of resolving this issue.

Forest Root Zone for _msdcs
In Active Directory, all client logons and lookups are directed to local domain controllers and global catalog servers through references to the SRV records in DNS. These SRV records were stored in a subdomain to an Active Directory domain that is known as the _msdcs subdomain.

In Windows Server 2008 R2, _msdcs is a separate zone in DNS. This zone, stored in the application partition, is replicated to every domain controller that is a DNS server. This listing of SRV records was moved mainly to satisfy the requirements of remote sites. In Windows 2000, these remote sites had to replicate the entire DNS database locally to access the _msdcs records, which led to increased replication time and reduced responsiveness. If you delegate the SRV records to their own zone, only this specific zone can be designated for replication to remote site DNS servers, saving replication throughput and increasing the response time for clients.

Source of Information : Sams - Windows Server 2008 R2 Unleashed (2010)

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