Differences Among A, CNAME, ALIAS, and URL records

A, CNAME, ALIAS, and URL records are all possible solutions to point a host name (“name”) to your site. However, they have small differences that affect how the client reaches your site.

A and CNAME records are standard DNS records. ALIAS and URL records are custom DNS records provided by DNSimple’s DNS hosting. Both of them are translated internally into A records to ensure compatibility with the DNS protocol.

Understanding the differences

These are the main differences:

• The A record maps a name to one or more IP addresses when the IP are known and stable.
• The CNAME record maps a name to another name. It should only be used when there are no other records on that name.
• The ALIAS record maps a name to another name, but can coexist with other records on that name.
• The URL record redirects the name to the target name using the HTTP 301 status code.

Important rules:

• The A, CNAME, and ALIAS records cause a name to resolve to an IP. Conversely, the URL record redirects the name to a destination. The URL record is a simple and effective way to apply a redirect for one name to another name, for example redirecting www.example.com to example.com.
• The A name must resolve to an IP. The CNAME and ALIAS records must point to a name.

Which one to use

Understanding the difference between A name and CNAME records will help you decide.

General rules:

• Use an A record if you manage which IP addresses are assigned to a particular machine, or if the IP are fixed (this is the most common case).
• Use a CNAME record if you want to alias one name to another name, and you don’t need other records (such as MX records for emails) for the same name.
• Use an ALIAS record if you’re trying to alias the root domain (apex zone), or if you need other records for the same name.
• Use the URL record if you want the name to redirect (change address) instead of resolving to a destination.

You should never use a CNAME record for your root domain name (e.g. example.com).