Examining Record Types

Before we delve into creating a zone (an administrative domain) in DNS, we need to talk about record types. We briefly touched upon the fact that DNS provides not only host name-to-IP address translation, but also mail server information.

A record type tells DNS what kind of information it is storing. This record type is also something you can explicitly query. For example, you can query the MX record for a domain to find out what mail server to use when sending a recipient in the domain mail. Services that rely on DNS (such as mail or name resolution) query a specific record in the DNS database for specific hosts. This drastically reduces the amount of traffic that is produced because you see only the data you explicitly asked for, and not the whole record. What makes this happen is the use of record types. With DNS, you have six main record types to keep in mind:

■ The Address record: The most common record in DNS is the Address record. An Address record is used to translate a host name to an IP address.

■ The Pointer record: A Pointer record is the reverse of an Address record. It translates an IP address to a host name.

■ The CNAME record: If you want to create an alias of one host to another, a CNAME entry is used.

■ The MX record: An MX record is used to define a Mail Exchanger for the domain (or zone) you have created.

■ The NS record: The NS record is used to define the name server for this domain.

■ The SOA record: The Start of Authority (SOA) is effectively the header for the zone in question. It contains information about the zone itself and is mandatory.

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