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 220.127.116.11
localhost IN A 127.0.0.1
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
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
www CNAME Server1
ftp CNAME Server1
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 18.104.22.168, the DNS server performing the query looks for a PTR record for 10.113.41.121.inaddr.arpa, which will have the host
name and IP address 22.214.171.124. The record for it would look like this:
10.113.41.121.inaddr.arpa. 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%System32Dns
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%system32dns 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
Until next time, best of luck in your studies.