Types of DNS Records and DNS terms

Zone transfer

Replicating DNS information to the other DNS servers within the namespace. The SOA does zone transfers.

Service Locator (SRV)

Defines the hostname and port number of servers providing specific services, such as a Directory Services server (Global catalog).

Time to Live (TTL)

If a request is not answered within the TTL time frame, the user receives an error message stating the server cannot find the requested DNS server.

Mail Exchanger (MX)

Maps a domain name to a email server list. This record identifies your e-mail servers within your domain. These point to a mail server. Usually reside on the Internet and is a service provided by ISPs.

IPv6 address (AAAA)

Maps a host name to its IP address by using a 128-bit IPv6 address

Address (A)

Maps a host name to its IP address by using a 32-bit IPv4 address. Is used most often for DNS lookups.

Forward lookup

Maps a hostname to its IP address. A and AAAA records are forward lookups.

Reverse lookup

Maps an IP address to its hostname. PTR records are reverse lookups. Needs to have a reverse lookup zone for setup.

Pointer (PTR)

Maps an IP address to the host name for the purpose of reverse lookup. You don't absolutely need a PTR record for every entry in your DNS namespace. These are usually associated with e-mail server records.

Start of Authority (SOA)

This is the zone's authoritative server. It maintains and manages all the records within its zone and replicates them (zone transfer) to the other DNS servers within the namespace. Identifies the primary name server for the zone. The SOA record contains the hostname of the server responsible for all DNS records within the namespace, as well as the basic properties of the domain. Every zone has a SOA. These tell the whole zone about its (the SOA) own information. Holds the following information: Source host Contact e-mail Serial number Refresh time Expire time TTL

Name Server (NS)

This record defines the name servers within your namespace. These servers are the ones that respond to your clients' requests for name resolution. These point the user to other DNS servers.

Canonical name (CNAME)

This record provides for domain name aliases within your zone. For example, you may have an FTP service and a web service running on the same IP address. CNAME records could be used to list both within DNS for you. CNAME records must always point to another domain name, never directly to an IP address.