How to Add a CNAME
Adding a CNAME record to your domain's DNS settings allows you to create new variations of your website address in the form of subdomains. For example, adding "blog" as a CNAME for the domain "mywebsite.com" creates the subdomain "blog.mywebsite.com". When a user goes to the new subdomain, she will go directly to the destination you entered in the CNAME record. To create a CNAME record, you must have administrator access to your domain hosting account.
Log into your account at the website of the company where you purchased your domain name. If you have a Web hosting account with another company, and you transferred DNS management to the new company's name servers, log into the Web hosting site instead. If you're not sure which company controls your DNS settings, first try the Web hosting company and then the domain registrar.
Find the website's DNS management page. Depending on which company you use, the location of this page on the website will vary. You can often find it by selecting "DNS Management," "DNS Settings," "DNS Hosts," "Zone Editor" or something similar. On some sites, you may have to first select the "Domains" option and then select the name of your domain.
Find the section of the DNS settings page that allows you to add a new record. In some cases, you may need to click "Add Record," "Edit" or something similar. The website will ask you for up to four pieces of information: a record type, a host name or alias, a value or destination, and a time delay or "TTL."
Set the record type to "CNAME," and then enter the new domain prefix in the host name or alias field. For example, if you are creating the "pictures.mywebsite.com" subdomain, enter "pictures" in this field. Do not add a period at the end of your entry -- you DNS editor will do this automatically.
Set the value or destination field to the location or address to which the new subdomain should point. For example, if you are creating a subdomain called "pictures.mywebsite.com" that should point to an image folder on your Web server, you might enter "mywebsite.com/data/images" as the value or destination. You can also point subdomains to other websites. For example, if you have Tumblr blog and want readers to be able to access it from your own website, you might create the subdomain "blog.mywebsite.com". In this case, you would enter "domains.tumblr.com." (including the last period inside the quotes) as the value or destination.
Leave the TTL setting at the default value and then save the new entry. The CNAME record should become active within four hours, although it can sometimes take up to eight hours for the new information to propagate to all of the other DNS servers on the Internet.
Tips & Warnings
- When you enter another domain name as the value or destination in a CNAME record, it's best to add a period at the end of the domain name to create a fully-qualified, unambiguous domain name. For example, when you add a period at the end of "domains.tumblr.com.", you are telling the DNS server that the entry ends in a domain name, and is not just a folder or subdomain of your own domain. While the extra period is not absolutely necessary, it may help DNS route requests more efficiently and reduces the possibility that your subdomain gets routed to the wrong host.