Title: DNS Records
Course: CIS 208: Linux/UNIX III: Intermediate System Administration, Networking, and Security ~ For IGNITE Review > Section: Learning Modules

DNS Records

The Domain Name System (DNS) uses various types of resource records to manage the hostnames and IP addresses within a domain.  These are some of the essential resource records.  Note that all of these except the PTR record are used in forward zones (resolving names to IP addresses) and PTR records are only used in reverse zones (resolving IP addresses to names).

Source: "Domain name space". Licensed under Public domain via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Domain_name_space.svg#mediaviewer/File:Domain_name_space.svg

- SOA - Start Of Authority record.  Contains the information about the domain including the master server, the contact, the serial number, and the refresh intervals.
- A - Address record.  An IPv4 address of the host.
- AAAA - Quad A record.  An IPv6 address of the host.
- MX - Mail Exchange record.  An incoming mailserver of host.
- NS - Name Server record.  A nameserver of the host.
- CNAME - Canonical Name record.  The actual hostname of the host.
- TXT - Text record.  Human readable information about the host.
- PTR - Pointer record.  A hostname of the IP address.

These records are included within the zone file of the master server for a domain.  The slave servers automatically receive updates, so only the master server's zone file needs to be updated. The master and slave servers are considered authoritative, which means they do not cache records--they have the latest version of all the records.

All other servers (the non-authoritative servers) may cache individual records, but do not automatically receive updates with the zone is updated.  This is the reason it is often said that it takes 24 hours for updates to DNS records.