vsftpd 绑定IP,只对内网开放，更安全。
在vsftpd.conf文件中加入:
listen_address=192.168.102.253
查询配置细节:man vsftpd.conflisten_address If vsftpd is in standalone mode, the default listen address (of all local interfaces) may be overridden by this setting. Provide a numeric IP address. Default: (none)
