Learn AD in 15 Minutes a Week: Microsoft DNS - Part 1 Page 3

DNS Zone Overview

A DNS zone is a contiguous portion of the domain namespace for which a particular DNS server has authority to resolve DNS queries. DNS namespaces are almost always divided into zones that store name information about one or more DNS domains or portions of a DNS domains.

In the Windows 2000 Active Directory domain structure there are three different zone types.

The Standard Primary zone contains a read/write version of the zone file that is stored in a standard text file. Any changes to the zone are recorded in that file and that file only. Any other copies of that zone are Secondary zone copies and are read only

The Standard Secondary zone contains a read-only version of a Primary zone file, and it is stored in a standard text file. Any changes to the zone are performed on the Primary zone file and are replicated to the Secondary zone file. You would create a Standard Secondary zone to create a copy of an existing Primary zone and its zone file, which allows the DNS name resolution workload to be distributed among multiple DNS servers.

Active Directory integrated zones store the DNS zone information in the Active Directory database rather than in a text file. Updates to the Active Directory integrated zone occur automatically during Active Directory replication. You do not need to manually configure DNS servers to specify update intervals as Active Directory maintains the zone information and replicates the information based on its own replication schedule.

The Active Directory integrated option is not available in the Change Zone Type dialog box until you implement Active Directory. If Active Directory is not present in your environment the option will be grayed out in the New Zone Wizard and the Change Zone Type dialog box from the DNS MMC.

DNS zone files contain the name resolution data for a zone and they also include resource records that contain database entries that contain various attributes of network systems. Below is a list of the most common resource records.

(A) records, sometimes called host records or address record, contain the name-to-IP address mapping information used to map DNS domain names to a host IP address on the network.

Alias records, normally referred to as CNAME (canonical name) records allow you to provide additional names to a server that already has a name in an A (host) resource record. This is how a Web server with a name of Server1 in a domain of Zandri.net "becomes" www.zandri.net as far as DNS resolution is concerned. There is an Alias record referencing www.zandri.net to Server1.zandri.net.

MX (Mail Exchanger) records specify the server where e-mail can be delivered in a given domain. When you have a Mail server named Mailbox.zandri.net and you want all mail for all_users@zandri.net to be delivered to this mail server (named Mailbox in this example), the Mail Exchanger resource record must exist in the zone for Zandri.net and must point to Mailbox.

NS (Name Server) records designate the DNS domain names for the servers that are authoritative for a given DNS zone.

PTR (Pointer) records are used for reverse look up queries. A reverse lookup query resolves an IP address to a name.  Reverse lookup zones are created in the in-addr.arpa domain to designate a reverse mapping of a host IP address to a host DNS domain name.

SOA (Start of Authority) records indicate the starting point of authority for a given DNS zone on a specific DNS server. The SOA resource record is the first resource record created when you add a new zone.

SRV (Service) records, sometimes referred to as Service Location records, contain registered services within the zone so that clients can locate these available services by using DNS. SRV records are mainly used to identify services in Active Directory.


Well, that wraps up this section of "Learn Active Directory Design and Administration in 15 Minutes a Week." I hope you found it informative and will return for the next installment.

If you have any questions, comments or even constructive criticism, please feel free to drop me a note.

I want to write solid technical articles that appeal to a large range of readers and skill levels and I can only be sure of that through your feedback.

Until next time, best of luck in your studies and remember:

I remember how my mother taught me RELIGION - "You better pray that will come out of the carpet."

This article was originally published on Dec 19, 2002
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