What is DNS and what are A, MX and CNAME records?


Distributed Name System (DNS) is an Internet protocol that connects text based domain names to their numeric IP addresses. i.e. DNS translates www.domain.com to an IP address.

Name Server:
Listens for and answers requests for DNS information. Each ISP and Hosting Company has their own set of Name Servers. When you register or transfer a domain, you specify which provider's Name Servers are authoritive for a domain. When someone
tries to email you or visit your website, their ISP's servers query the authoritive Name Servers to find out which IP addresses to use.

Resource Records
An entry in the DNS that defines an Internet resource.

  • "A" Records:
    An "Address" record maps a name to an IP address. e.g.

    www.domain.com IN A

    mail.domain.com IN A
  • "CNAME" Records
    "Canonical Name" records allow you to set aliases for existing address records e.g.

    pop.domain.com IN CNAME mail.domain.com.

    pop3 IN CNAME mail

    mail IN A

    In the case above pop.domain.com and pop3.domain.com point to the same location. The pop3 line shows an abbreviated way of defining the record.
  • "MX" Records:
    "Mail eXchanger" records specify which servers are to be used for email delivery. Multiple mail servers can be specified with different preferences. This creates fault tolerance in the event a mail server is unreachable. The server with the lowest preference value is the first server that other mail servers attempt to contact. If that server is not available, external mail servers progress down the list to the server with the next lowest preference value. e.g.

    smtp IN MX 5 mail

    smtp2 IN MX mailbackup.isp.com.

    mail IN A

A * prefix can be used as short-hand for all prefixes. e.g.

* IN A

This maps www.domain.com ftp.domain.com etc. to

A @ prefix can be used as short-hand for a blank prefix. e.g.

@ IN A

This maps domain.com to

When you setup a domain, these records are set to the defaults for our servers.

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