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Adding a Resource Record to a Forward Lookup Zone

Updated: May 9, 2008

Applies To: Windows Server 2008

Resource records contain the information that a Domain Name System (DNS) zone maintains about the resources (such as hosts) that the zone contains. A typical resource record consists of the name (host) of the resource record owner, information about how long the resource record can remain in the cache, the resource record type (such as a host (A or AAAA) resource record), and data that is specific to the record type (such as the host's address). You can add resource records directly, or they can be added automatically when Windows-based, Dynamic Host Configuration Protocol (DHCP)–enabled clients join a network. This process is known as dynamic update.

The most common resource records to be added to a forward lookup zone are the following:

  • Host (A or AAAA): Host (A or AAAA) resource records associate DNS domain names of computers (or hosts) to their IP addresses. They can be added to a zone in several ways:

    • You can manually create a host (A or AAAA) resource record for a static TCP/IP client computer using the DNS Manager snap-in.

    • Windows clients and servers use the DHCP Client service to dynamically register and update their own host (A or AAAA) resource records in DNS when an IP configuration change occurs.

    The host (A or AAAA) resource record is not required for all computers, but it is required for computers that share resources on a network or otherwise need to be accessed by other computers. Most host (A or AAAA) resource records that are required in a zone can include other workstations or servers that share resources, other DNS servers, mail servers, and Web servers. These resource records make up the majority of resource records in a zone database.

  • Alias (CNAME): Alias (CNAME) resource records are also sometimes called canonical name resource records. By using these records, you can have more than one name to point to a single host. This makes it easy to do such things as host both a File Transfer Protocol (FTP) server and a Web server on the same computer. For example, the well-known server names (ftp, www) are registered using alias (CNAME) resource records that map to the DNS host name, such as "server-1", for the server computer that hosts these services.

    Alias (CNAME) resource records are recommended for use in the following scenarios:

    • When a host that is specified in a host (A or AAAA) resource record in the same zone must be renamed.

    • When a generic name for a well-known server, such as www, must resolve to a group of individual computers (each with individual host (A or AAAA) resource records) that provide the same service, for example, a group of redundant Web servers.

    • When you rename a computer with an existing host (A or AAAA) resource record in the zone, you can use an alias (CNAME) resource record temporarily to allow a grace period for users and programs to switch from specifying the old computer name to using the new one. To do this, you must first ensure the following:

      • For the new DNS domain name of the computer, a new host (A or AAAA) resource record is added to the zone.

      • For the old DNS domain name, an alias (CNAME) resource record is added that points to the new host (A or AAAA) resource record.

      • The original host (A or AAAA) resource record for the old DNS domain name (and its associated pointer (PTR) resource record, if applicable) is removed from the zone.

    ImportantImportant
    You cannot create an Alias (CNAME) resource record for a name if there is already a DNS record for that name. This includes the root of a zone; that is, you cannot create an alias (CNAME) record for the root of a zone.

    When you use an alias (CNAME) resource record for renaming or creating an alias for a computer, set a temporary limit on how long the record is used in the zone before it is removed from DNS and then delete the record from the zone when the time limit has passed. If you forget to delete the alias (CNAME) resource record and later its associated host (A or AAAA) resource record is deleted, the alias (CNAME) resource record can waste server resources by trying to resolve queries for a name that is no longer used on the network.

    The most common or popular use of an alias (CNAME) resource record is to provide a permanent alias domain name for generic name resolution of a service-based name, such as www.contoso.com, to more than one computer or one IP address that is used on a Web server.

  • Mail Exchanger (MX): E-mail applications use the mail exchanger (MX) resource record to locate a mail server based on a DNS domain name in the destination address for the e-mail recipient of a message. For example, a DNS query for the name "sales.contoso.com" finds a mail exchanger (MX) resource record, which enables an e-mail application to forward or exchange mail to a user with the e-mail address "user@contoso.com."

    The mail exchanger (MX) resource record shows the DNS domain name for the computer or computers that process mail for a domain. If multiple mail exchanger (MX) resource records exist, the DNS Client service attempts to contact mail servers in the order of preference from lowest value (highest priority) to highest value (lowest priority).

To complete this task, you can perform the following procedures:

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