note:網址 hostname中的底線網址中的 主機名稱 hostname 含有「底線」符號時
在 IE 中會停掉該網址的 cookie
例如在 abc_xyz.foo.com 就讀不到任何的 cookie
但 FireFox、Chrome 則正常
「底線」在 DNS 的規定中是不能使用的
參考：
DNS Tricks and Tips
Legal characters in hostnames
Domain names can contain almost any characters. However, host names and mail domain names have restrictions which only allow the use of characters `a-z', `A-Z', `0-9', and `-' (dash or minus sign). The `/' and `_' (divide or slash and underscore) characters are not legal. Note that hostnames include the owners of A and MX records and .in-addr.arpa PTR records, and the data fields of MX and .in-addr.arpa PTR records: in other words, almost all currently used DNS entries! The current releases of the BIND name server software enforce these restrictions. 20-Nov-1997, 10-Apr-1996
hostname 只能用 大小寫字母、數字以及減號
