DNS Records and Linux

Each DNS zone file contains records that consist of a number of entries. As a Linux user or administrator, these records will guide Internet users to your website. The entries are also known as resource records and can vary ever so slightly in format. The following sections examine the most common record types.

SOA Record

Every database file starts with an SOA (Start of Authority) record. This record identifies the zone and contains several other parameters, including the following:

  • Source Host: The name of the primary server (with the read/write copy of the file).

  • Contact E-mail: E-mail address for the administrator of the file.

  • Serial Number: The incrementing version number of the database.

  • Refresh Time: The delay in seconds that secondary servers wait before checking for changes to the database file.

  • Retry Time: The time in seconds that a secondary server waits before another attempt if replication fails.

  • Expiration Time: The number of seconds on secondary servers before the old zone information is deleted.

  • Time to Live (TTL): The number of seconds that a caching-only server can cache resource records from this database file before discarding them and performing another query.

NS record

The Name Server record simply specifies the other name servers for the domain, or maps a domain name to that of the primary server for the zone.

A record

The Address record holds the IP address of the name.

CNAME record

The Canonical Name record is an alias field allowing you to specify more than one name for each TCP/IP address.

MX record

The Mail Exchange record specifies the name of the host that processes mail for this domain.

HINFO record

The Host record is the record that actually specifies the TCP/IP address for a specified host. All hosts that have static TCP/IP addresses should have an entry in this database.

PTR record

Pointer records are used for reverse lookup entries. They specify the IP address in reverse order and the corresponding host name.

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