没看太懂. 第一种适用于子域名, 第二种用于二级域名
http://www.tumblr.com/docs/en/custom_domainsIf you are using a subdomain that has three or more levels, like
www.mywebsite.com or
blog.mywebsite.com, follow the registrar's instructions to point the CNAME record for the subdomain to
domains.tumblr.com.
OR
If you are using a domain that has only two levels, like
mywebsite.com, follow the registrar's instructions to point the domain's A-record (IP address) to 66.6.44.4.