DNS隧道工具使用
http://www.freebuf.com/sectool/112076.html
http://netsec.ccert.edu.cn/zhengming/2011/11/01/%E8%BD%AC%E8%BD%BD%EF%BC%9Adns-tunnel%E7%9A%84%E5%8E%9F%E7%90%86%E5%8F%8A%E5%AE%9E%E6%88%98/
https://wenku.baidu.com/view/84d8c843b307e87100f69605.html
http://big5.jinri-toutiao.com/id/594012.html
http://m0d9.me/2016/10/20/DNS-trick/
http://www.mottoin.com/85443.html
http://docs.ioin.in/writeup/blog.heysec.org/_archives_854/index.html