5 Start the DNS service by clicking the Start DNS button. Then open the Network pref-
erences pane on your Mac OS X Server and enter the IP address and domain name of
your server. Apply the changes. Your server is now running DNS and looking at itself
to ensure that any other service—such as Lightweight Directory Access Protocol
(LDAP)—will respond to either the IP address or the computer’s fully qualified
domain name.
DNS Zone Records
Each zone contains a number of records. These records are requested when a client com-
puter needs to translate a domain name (like www.pretendco.com) to an IP number. Web
browsers, email clients, and other network applications rely on zone records to contact
the appropriate server. You create records by adding machines to a zone in Server Admin.
In some cases, you are adding secondary names for the same machine. For example,
server17.pretendco.com can also be www.pretendco.com and/or smtp.pretendco.com.
96 Providing Basic DNS Service
Your master zones records will be queried by other computers across the Internet so they
can connect to your network services. There are several kinds of DNS records. The follow-
ing are the records that are available for configuration by Server Admins user interface:
Address (A): Also known as a machine record. Stores the IP address associated with a
domain name. An A record is created for each machine entry added to a zone.
Canonical name (CNAME): Stores the “real name of a server when given a nick-
name or alias. For example, mail.pretendco.com might have a canonical name of
mailsrvr1.pretendco.com. A CNAME record is created for each entry in the Alias
field when adding a machine to a zone.
Mail exchange (MX): Stores the name of the computer that is used for email for a
domain. An MX record is created when you specify that a machine is a mail server.
You can have more than one MX record for your domain pointing to different
servers. Lower numbers are given priority over higher numbers when users attempt
to use the mail servers on your network.
Service (SRV): Service records store the information about various services, such as
LDAP, Jabber, and Simple Mail Transfer Protocol (SMTP). These services are then
mapped to the proper IP address and resolved to their respective domain name.
Pointer (PTR): Automatically created. Stores the domain name of a given IP address
(reverse lookup). A PTR record maps an IP address to a computer’s DNS name. The
pointer record contains the four octets of the IP address in reverse order followed by
in-addr.arpa. (For example, becomes
Mac OS X Server simplifies the creation of these records by focusing on the computer name
being added to the zone rather than the records themselves. As you add a computer record
to a zone, Mac OS X Server creates the proper pointer zone record that resolves to a certain
computer address.
The term fully qualified domain name (FQDN) refers to the entire address
of a host computer. For example, “sales.apple.com is an FQDN, whereas “sales is a
relative domain name. To indicate that a domain name is fully qualified, add a trailing
dot to it (which Mac OS X Server v10.5 automatically does when selecting the check-
box for Fully Qualified). For example, “sales.apple.com. indicates that this is not a
relative domain name.
DNS Zone Records 97
Add Records to a DNS Server
DNS is a complicated topic that covers a wide range of configuration options and settings.
This lesson does not cover in-depth DNS configuration. You will add information to your
DNS configuration that will enable you to associate a friendly name with your computer
and see the effects of that change. You will be adding several types of records to permit the
server to respond to additional names—such as www.pretendco.com—that will be used in
later lessons. You will also be adding a record for your Mac OS X computer, so it can also
resolve to a name.
1 Within Server Admin, select the DNS service if its not already selected and click the
Zones icon in the toolbar. Select the Primary Zone for your server. Click the disclosure
triangle to view the machine record, but do not click the machine record yet.
2 Click the add button adjacent to the Mail Exchangers entry box and enter the word
mail in the Hostname list. Then enter the number 10 in the Priority list and click Save.
The FQDN will appear in the list along with the priority value for that MX record.
98 Providing Basic DNS Service
3 Select the machine record from the list, click the Add Record button, and choose Add
Machine (A).
4 Click the add button to create a machine record and edit the IP address accord-
ingly. Click Save.
DNS Zone Records 99

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