http://www.ibm.com/developerworks/cn/linux/network/l-netip/index.html
http://blog.chinaunix.net/u2/82249/showart_1905848.html
http://blog.chinaunix.net/u2/82249/showart_1841083.html
http://blog.chinaunix.net/u2/82249/showart_1856217.html
http://blog.chinaunix.net/u2/82249/showart_1841161.html
自己写 Netfilter 匹配器
http://blog.chinaunix.net/u2/82249/showart_1848704.html
Patch-O-Matic 定制netfilter kernel modules
http://cha.homeip.net/blog/archives/2006/01/netfilter_exten.html