Address (A) records direct a hostname to a numerical IP address. For example, if you want mycomputer.yourdomain.com to point to your home computer (which is, for example, 192.168.0.3), you would enter a record that looks like:
Important: You must put a period after the hostname. Do not put periods after IP addresses.
CNAME allows a machine to be known by one or more hostnames. There must always be an A record first, and this is known as the canonical or official name. For example:
yourdomain.com. A 192.168.0.1
Using CNAME, you can point other hostnames to the canonical (A record) address. For example:
ftp.yourdoman.com. CNAME yourdomain.com.
mail.yourdomain.com. CNAME yourdomain.com.
ssh.yourdomin.com. CNAME yourdomain.com.
CNAME records make it possible to access your domain through ftp.yourdomain.com, mail.yourdomain.com, etc. Without a proper CNAME record, you will not be able to connect to your server using such addresses.
Entering a CNAME record
If we wanted home.site-helper.com to point to site-helper.com, we could enter the record in two ways:
The first method allows you to simply enter the subdomain. Do not put a period after the subdomain name.
The second method requires you to enter the entire hostname, followed by a period.