在apache的虚拟主机中，如果书写了。ServerAlias www.a2.com www.a3.com这样的语句，就可以给虚拟主机增加多个域名，而且这些域名都访问同一个站点。
#Listen 81
<VirtualHost *:80>
ServerName www.a1.com:80
ServerAdmin webmaster@localhost
DocumentRoot "F:/webserver/htdocs/a1"
ServerAlias www.a2.com www.a3.com
ErrorLog "logs/a1-error.log"
CustomLog "logs/a1-access.log" common
<Directory "F:/webserver/htdocs/a1">
Options Indexes FollowSymLinks Includes
IndexOptions FancyIndexing ScanHTMLTitles
AllowOverride All
Order allow,deny
Allow from all
</Directory>
ScriptAlias /cgi-bin/ "F:/webserver/htdocs/a1/cgi-bin/"
<Directory "F:/webserver/htdocs/a1/cgi-bin/">
AllowOverride None
Options Indexes FollowSymLinks ExecCGI
Order allow,deny
Allow from all
</Directory>
</VirtualHost>
上面的代码会让a1,a2,a3 三个域名都访问到同一个空间。