一个很好的防火墙源代码，这是网上搜集来的，具体功能大家自己下载研究吧-A good firewall source code, which is collected to the Internet, and the specific function of everyone to download and study it. . . .

举例了几个流行的防火墙实现原理。讲的很具体，适合初学者和深入研究。反正就是好文啊。-For example the principles of several popular firewalls. Talking about very specific, suitable for beginners and in-depth study. Anyway, it is a good text ah.