一个完整的域名由两个或两个以上部分组成，各部分之间用英文的句号“.”来分隔，例如下列域名：yahoo.com,sina.com。在一个完整的域名中，最后一个“.”的右边部分称为顶级域名或一级域名；最后一个“.”的左边部分称为二级域名；二级域名的左边部分称为三级域名，三级域名的 A complete domain name consists of two or more parts, separated by the English period “.”, For example, the following domain names: yahoo.com, sina.com. The right part of the last “.” In a complete domain name is called the top-level domain or first-level domain name; the left part of the last “.” Is called the second-level domain name; the left- Third-level domain name