据http://technet.microsoft.com/en-us/library/active-directory-maximum-limits-scalability(v=ws.10).aspx,一个DN的最大长度为255个字符。

According to http://technet.microsoft.com/en-us/library/active-directory-maximum-limits-scalability(v=ws.10).aspx, the maximum length of a DN is 255 characters.