Two Types of Custom Domains

Using Blogger's Custom Domain facility you can redirect your blogspot blog to a brand new domain or URL and it will cost you only 10$. Blogger is not however responsible for domain management services which are offered by Godaddy.com or Enom.com.

Custom Domains work by using changed DNS records in DNS servers. There are two types of Custom Domains...........


The two types of Custom domains are :
1. Blogspot to Custom Domain.
2. Blogspot to Custom Subdomain.

When you buy a domain name (mysite.com) you can redirect your blog to it (www.mysite.com). This is the first type of Custom Domain.

In the second type you create subdomains within your domain (mysite.com) like :
blog.mysite.com
docs.mysite.com
mail.mysite.com
start.mysite.com
blog2.mysite.com
blog3.mysite.com
You can then redirect one blog to each of the subdomains listed above. These subdomains can be created in your account with Godaddy/Enom. This free account is created when you buy the domain name from Blogger.

The control panel login page is at https://www.google.com/a/cpanel/MYSITE.COM/Advanced. 
Be sure to replace 'MYSITE.COM' with your actual domain name. Login to your domain manager by clicking the link in the email you got from Google Apps when you bought the domain.

The configuration for the two types of Custom Domains is different :

1. BLOGSPOT TO CUSTOM DOMAIN :

In this type set the CNAME record for www.mysite.com  only to point to ghs.google.com.
Do not set CNAME record for mysite.com.

Then set the A record for mysite.com as follows :
:

MYSITE.COM. A IN 216.239.32.21
MYSITE.COM. A IN 216.239.34.21
MYSITE.COM. A IN 216.239.36.21
MYSITE.COM. A IN 216.239.38.21





Lastly go to Settings----->Publishing in your blog and click on Switch to Custom Domains. Then click on Advanced Settings and in Your Domain box type :
www.mysite.com
Enter the Captcha word and save settings.

2. BLOGSPOT TO CUSTOM SUBDOMAIN :

In this type you will redirect your blogspot blog to blog.mysite.com. 
For this set the CNAME of both :

blog.mysite.com AND www.blog.mysite.com to ghs.google.com.



Next go to Settings----->Publishing in your blog and click on Switch to Custom Domains. Then click on Advanced Settings and in Your Domain box type :
mysite.com
Enter the Captcha word and save settings.

Source : http://www.blogdoctor.me/2008/11/two-types-of-custom-domains.html