Differences Between A and CNAME Records

The A and CNAME records are the two common ways to map a hostname (“name”) to one or more IP addresses. There are important differences between these two records.

Understanding the differences

The A record points a name to a specific IP. If you want blog.dnsimple.com to point to the server 185.31.17.133 you’ll configure:

blog.dnsimple.com.     A        185.31.17.133

The CNAME record points a name to another name instead of to an IP. The CNAME source represents an alias for the target name and inherits its entire resolution chain.

How we use them

Let’s use an example:

blog.dnsimple.com.      CNAME   aetrion.github.io.
aetrion.github.io.      CNAME   github.map.fastly.net.
github.map.fastly.net.  A       185.31.17.133

We use GitHub Pages, and we set blog.dnsimple.com as a CNAME of aetrion.github.io, which is a CNAME of github.map.fastly.net, which is an A record pointing to 185.31.17.133. This means blog.dnsimple.com resolves to 185.31.17.133.

Which one to use

An A record points a name to an IP. A CNAME record can point a name to another CNAME or to an A record.