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Dated: Jul. 16, 2012

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Something About DNS Records

DNS records are the objects that are created either manually by the DNS administrators or automatically by the DNS servers themselves. A DNS server can have indefinite numbers of records and each DNS record is helpful in resolving the query of its own type. For example a Host (A) record in DNS server helps resolving a hostname to its corresponding IPv4 address whereas Host (AAAA) record resolves hostname to its corresponding IPv6 addresses.

Although there are many types of DNS records that a DNS database can have, there are few of them that are most commonly used in almost every production environment.

For security reasons administrators in many organizations disable automatic DNS updates that prevents DNS servers from updating their database and adding DNS records automatically. However in some organizations administrators allow DNS servers to add DNS records automatically and this process is technically called dynamic DNS updates.

If administrators plan to configure DNS servers to dynamically update their records, they have two options from which they are required to select any one. The two options are:

1. Secure only – This option is only available if there is a domain controller present in the network. When this option is selected, DNS only adds the records of the computers that are the members of the domain. In the networks where domain controllers are present, this is the most recommended configuration in order to make the network secure.
2. Non secure and secure – This option is available in both domain-client and workgroup based network setups. When this option is selected, DNS server dynamically updates its records by adding the records of any computer that requests the DNS server to register it. This option is mostly selected in workgroup networks where no domain controllers are present and Secure only option is not available.

DNS Records Types

As mentioned above, there are several types of DNS records that a DNS server supports, there are some of them that are most commonly used in almost every organization. Such most commonly used DNS records types include:

• Host (A) – These records resolve host names to their IP address when the version of the IP address is IPv4. In DNS database, the hostname of the computer is mentioned along with its corresponding IP address and the entire set is known as a Host (A) record.
• Host (AAAA) – These records are identical to the Host (A) records except that they resolve IPv6 addresses instead of IPv4.
• MX – These record types are used to resolve mail server requests and are called Mail Exchanger records.
• CNAME – These records are also referred to as alias names records. These records are manually created by the administrators in order to provide alias names (user-friendly names) for the hosts that have their hostnames according to the organizations’ naming conventions. CNAMEs are mostly used when hostnames are to be kept secret and still computers are to be made accessible from the outer world. For example, if a hostname of a computer is internal.accounts.domain.com, administrators can create a CNAME (alias name) for this computer that may have a user-friendly name such as main.account.com or www.account.com.

Host (A) and Host (AAAA) records can also have their corresponding PTR pointer records for reverse lookups. This means that with the help of PTR records, the DNS servers resolve IP addresses to their corresponding hostnames. In order to create PTR records, Reverse Lookup Zones for the domains must be configured in the DNS servers.

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