Apple Mac OS X Server (Administrator’s Guide) - Manual (Page 516)

516 Chapter 14
Before You Set Up DNS Service
This section contains information you should consider before setting up DNS on your
network. The issues involved with DNS administration are complex and numerous. You
should only set up DNS service on your network if you are an experienced DNS administrator.
DNS and BIND
You should have a thorough understanding of DNS before you attempt to set up your own
DNS server. A good source of information about DNS is DNS and BIND, 4th edition, by Paul
Albitz and Cricket Liu (O’Reilly and Associates, 2001).
Note: Apple can help you locate a network consultant to implement your DNS service. You
can contact Apple Professional Services and Apple Solutions Experts at:
http://www.apple.com/services/
http://experts.apple.com/
Setting Up Multiple Name Servers
You should set up at least one primary and one secondary name server. That way, if the
primary name server unexpectedly shuts down, the secondary name server can continue to
provide service to your users. A secondary server gets its information from the primary
server by periodically copying all the domain information from the primary server.
Once your name server learns a name/address pair of a host in another domain (outside the
domain it serves), the information is cached, which ensures DNS services are available. DNS
information is usually cached on your name server for a set time, referred to as a time-to-live
(TTL) value. When the TTL for a domain name/IP address pair has expired, the entry is
deleted from the name server’s cache and your server will request the information again as
needed. (The entry is never deleted from the domain owner’s DNS server.)
Using DNS With Mail Service
If you plan to provide mail service on your network, you must set up DNS so that incoming
mail is sent to the appropriate mail host on your network. When you set up mail service, you
define a series of hosts, known as mail exchangers or MX hosts, with different priorities. The
host with the highest priority gets the mail first. If that host is unavailable, the host with the
next highest priority gets the mail, and so on.
For example, let’s say your mail server’s host name is “reliable” in the “example.com”
domain. Without an MX record, your users’ mail addresses would include the name of your
mail server computer, like this:
[email protected]