DNS Records Overview

Aim of this article:

This article gives a brief explanation about what the Domain Name system is, and explains what the various types of DNS record are and the WHOIS database.

What is DNS?

DNS stands for Domain Name System, and relates a domain name such as www.zen.co.uk to an IP address (or physical server). Every time you type a Web address into your browser a DNS request is made to find out the IP address for the Web server it is hosted on.  DNS requests are also made to locate the mail server responsible for a domain when you send an e-mail.

All the DNS records for a particular domain name are held on a DNS server. DNS servers are maintained by various different domain hosting companies. A couple of DNS servers are said to be authoritative for each domain, and are the servers that get checked by other DNS servers in order to find out information for that domain name. Usually the Authoratative DNS servers for your domain name are maintained by your domain name hosting company.

The different types of DNS records:

There are several different records that can be set up for a domain name, which are explained below: The first 3 types of record are the most common ones.

• A Record: This points a domain name (or a subdomain) such as www.zen.co.uk to an IP address (the physical server), and amongst other things tells your browser what server to look on when a website address is typed in. These are the most common types of record.
  
  Example: www.zen.co.uk -> 212.23.2.197
  
  
• MX Record: This is used by e-mail servers to determine where to send the e-mail to. Usually these point to an A record, such as mailcluster.zen.co.uk. You can set up more than one MX record, and give them a preference number, so that the MX record with the lowest preference number is tried first, and if that is unavailable then the next one is tried.
  
  Example: zen.co.uk  MX preference = 10  mail exchanger = mailcluster.zen.co.uk.
  
  
• CNAME Record: (Canonical Name) This type of record points a domain name (or subdomain) to another domain name (or subdomain) You can make a domain easier to maintain if you have serveral subdomains by setting up one A record and then use CNAMES to point all the subdomains to the first A record. Therefore if you needed to update the IP address the A record was pointed to all the subdomains would be updated automatically.

The following types of record can be changed by your domain provider, but there are only limited circumstances in which you would wish to do so.

• NS Record: This record says what name servers to use for the domain name. normally these are set to the domain hosting companies server's, but sometimes a registrant will wish to run their own name servers.
  
  Example: zen.co.uk  nameserver = ns0.zen.co.uk
  
  
• TXT Record: (Text record) This type of record can be used to put an arbitrary piece of information up against a domain.

The record types below are not usually able to be changed by your domain host, and are included for information only.

• SOA Record: (Start of Authority) This type of record is used to cut up the domain space into distinct areas of authority. For example .com and .uk are different authorities, just as domain1.com and domain2.com are different authorities.
• PTR Record: (Pointer or Reverse DNS record) This type of record is commonly used to point an IP address to a domain name (hence the name reverse DNS.) Unlike other types of record this is not maintained by your domain name host, but instead is maintained by the authority for your IP address (usually the Internet Service Provider) See the Related Article if you have a Zen Internet connection and require a reverse DNS record.

The WHOIS Database:

Each Registrar holds a publicly accessible database that contains information about the domain name holders. For example, Nominet maintain the WHOIS database for .uk domains. As the authority for .com domains is shared amougst several registrars, they each maintain their own WHOIS database.

In order to see the information in the database you can use the whois search facility on the Registrar's site, or you can use a tool which searches all databases, such as the facility at www.dnsstuff.com

Usually the WHOIS database contains some contact information for the owner of the domain name, such as the owner's name and address. Your domain host can update the information in this database for you.