如何通过web.config设置网站默认页

<configuration>
    <system.web>
        <compilation debug="true" targetFramework="4.0" />
    </system.web>
  <appSettings>
  </appSettings>
  <system.webServer>
    <defaultDocument>
      <files>
        <add value="index.aspx" />
      </files>
    </defaultDocument>
  </system.webServer>
</configuration>