Before you can enroll for an SSL Server Certificate, you must generate a Certificate Signing Request (CSR) from your web server software. During the creation of the CSR, the following fields must be entered: Organization (O), Organizational Unit (OU), Country (C), State (S), Locality (L), and Common Name (CN). The Common Name field is often misunderstood and filled out incorrectly.
The Common Name is typically composed of Host + Domain Name and will look like www.yoursite.com or yoursite.com. SSL Server Certificates are specific to the Common Name that they have been issued to at the Host level.
The Common Name must be the same as the Web address you will be accessing when connecting to a secure site. For example, an SSL Server Certificate for the domain domain.com will receive a browser warning if accessing a site named www.domain.com or secure.domain.com, as www.domain.com and secure.domain.com are different from domain.com. You would need to create a CSR for the correct Common Name.
By default all Basic, Wildcard and Enterprise EV certificates ordered from SSL.com will automatically add www. to any domain name registered. You can thus secure www.domain.com when filling out the Common Name field automatically – just enter your own domain.com and your certificate will automatically cover domain.com AND www.domain.com.
When a Certificate will be used on an Intranet (or internal network), the Common Name may be one word, and it can also be the name of the server.