Learn AD in 15 Minutes a Week: Microsoft DNS - Part 2 Page 3

Name Server (NS) records designate the DNS domain names for the servers that are authoritative for a given DNS zone and may list additional name servers within the record. The following is an example of an NS record:

@ IN NS server2.zandri.net.

[NOTES FROM THE FIELD] - The at symbol (@) in a database file indicates "this server" and the IN indicates an Internet record.

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

The following are examples of host records:

server1        IN A

localhost     IN A

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. An Alias record is referencing www.zandri.net to Server1.zandri.net. Some examples of this are listed below:

www              CNAME Server1
ftp                 CNAME Server1

PTR (Pointer) records are used for reverse lookup 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.

As we mentioned earlier, to perform a successful reverse lookup of a given IP address such as, the DNS server performing the query looks for a PTR record for, which will have the host name and IP address The record for it would look like this: IN PTR Server1.Zandri.net.

[NOTES FROM THE FIELD] - Reverse lookup zones are not a requirement; they are an optional configuration.

The CACHE.DNS file contains the records of the root DNS servers. The cache file is basically the same on all name servers, and it must be present for a DNS server to properly handle a query outside its zone.

The file is provided by default with the Windows 2000 DNS Server and has the current records for all of the root servers on the Internet. It is stored in the %SystemRoot%\System32\Dns folder that DNS is installed on a Windows 2000 Server.

If you are running DNS for internal use and not for connections for forwarding to the Internet, the CACHE.DNS file should be replaced to contain the name server's authoritative domains for the root of the private network.

[NOTES FROM THE FIELD] - In certain situations, the CACHE.DNS file in the %systemroot%\system32\dns folder is replaced, and it does not update the root hints listed in the DNS Manager. This can happen because the DNS server is a domain controller and is configured to load zone data on startup from Active Directory and the registry. This behavior occurs when the root hints specified in the Active Directory have been deleted, modified, incorrectly entered, or damaged.

Additional information on this can be found in Microsoft's Knowledge Base Article - Q249868 Replacing Root Hints with the Cache.dns File

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.

This article was originally published on Jan 6, 2003
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