DNS Concepts for Lion Server - dummies

By John Rizzo

When you configured Lion Server, the server assistant may have created a master zone with reverse lookup and a machine record for your primary DNS name. A DNS zone is an organization entity that contains different types of records that relate to a domain. You could have a zone that contained IP addresses for servers in the acmehigh.edu domain, such as www.acmehigh.edu and mailserver.acmehigh.edu.

A master (primary) zone contains all the records for the zone, and it is the Internet’s authority on that domain. A secondary, or slave, zone contains copies of master zone information that is stored on another server.

A DNS zone can contain several types of records. Here are the most common:

  • Machine record, also called Address (A): This basic record holds the IP address for a domain name for a server or service.

  • Canonical name (CNAME), also called an alias: You can use CNAMEs to resolve multiple domain names to one IP address (such as www.abc.com, ourserver.abc.com, and mail183.abc.com). For example, you might have a DNS zone with a CNAME record and an A record, as follows:

    www.abc.com. CNAME ourserver.abc.com.
    ourserver.abc.com. A

    In this case, when there is a lookup for www.abc.com, the IP address is returned. (Note that a dot is always used in domain names in DNS records.)

  • Mail exchange (MX) record: This identifies a computer as a mail server. MX records are not created by Server Assistant during installation/configuration.

  • Service (SRV) record: This identifies services that are hosted by one or more servers. It maps requests for the service to an IP address.

To a certain degree, Lion Server automates working with records. Server Admin asks you for information about the computer you’re adding to the zone, and it creates the zone record that resolves to the computer’s IP address. The focus is on the computer rather than the zone records.

Server Admin also automatically creates a reverse lookup zone when you create a master zone. A reverse lookup zone supplies a corresponding domain name when an IP address is presented by another computer.