Here are the links I learned from:
https://www.mail-archive.com/openvpn-users@lists.sourceforge.net/msg03394.html
https://www.mail-archive.com/openvpn-users@lists.sourceforge.net/msg03776.html
https://openmaniak.com/openvpn.php
https://help.ubuntu.com/lts/serverguide/openvpn.html
https://wiki.debian.org/OpenVPN
https://blog.cavebeat.org
https://wiki.archlinux.org/index.php/OpenVPN
http://dcamero.azurewebsites.net/openvpn-obfsproxy.html
http://www.thekelleys.org.uk/dnsmasq/docs/
http://www.rjsystems.nl/en/2100-adv-routing.php
http://www.tldp.org/HOWTO/Adv-Routing-HOWTO/lartc.rpdb.multiple-links.html
http://www.cyber.com.au/~twb/doc/dual-uplink.txt
https://www.agwa.name/blog/post/hardening_openvpn_for_def_con
http://greycoder.com/
https://prism-break.org/en/
http://www.sbprojects.net/projects/raspberrypi/tor.php
http://www.gl-inet.com/
http://enochma.com/page/3/
http://www.jianshu.com/p/2f51144c35c9
http://www.figotan.org/2016/05/04/cook-your-own-vpn/
http://shadowsocks.blogspot.sg
http://hyspace.io/posts/2015/08/22/纪念shadowsocks/
https://biergaizi.info/archives/2013/02/1621.html
https://sodatea.github.io/2015/12/23/all-i-know-about-the-wall/
http://igfw.net/archives/12556
https://www.raspberrypi.org/forums/viewtopic.php?f=36&t=135170
http://dcamero.azurewebsites.net/shadowsocks-ubuntu-1510-windows.html
https://scramblevpn.wordpress.com
https://plus.google.com/+GhostAssassin/posts/TtWFAQmSMVE
https://www.zhihu.com/question/28252105/answer/53481328