'telnet' is not recognized as an internal or external command

在研究Sinatra的时候，按书操作telnet 0.0.0.0 4567 ，发现提示：'telnet' is not recognized as an internal or external command

谷歌一把才知道Win7, Vista, Windows Server 2008 R2下telnet默认是不安装的，于是

解决方法：Start—>Control Panel—>Programs and Features-->Turn Windows Features on or off

选中telnet client

确定即可。