什么是二级域名呢
听说申请域名的时候给两个域名，一个是带www的，一个是不带的，又听说不带www的就是二级域名，不知是这样吗，还有，有没有三级域名、四级域名呢，干脆N级域名呢。
------解决方案--------------------
我说了要看服务，国际上没有这个收费，只是看DNS服务商是否提供，也就是说各家不同，从免费到天价都有可能
理论上～应该免费，但这个也占服务器资源，所以服务商也可能限制，大商家就有能力无限添加
如果你的注册商不提供多级域名，但可以让你修改指定DNS，你可以指定到一个另外的免费或收费的DNS服务商那里
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