Linux防火墙分析

Linux Firewall Analysis

描述了在Linux操作系统环境下防火墙的工作过程，对防火墙中包过滤工作过程的每一步从功能、流程上进行了详细的描述，并给出了包过滤规则工作流程图；同时，对防火墙的核心包过滤函数ip_fw_check（）进行了详细的介绍，分析了其函数参数、返回值和工作流程以及防火墙链结构Ip_fw，全面说明了Linux操作系统环境下防火墙的主要工作过程，明确了Linux操作系统下防火墙规则如何对数据流进行判断和控制管理．最后，给出了Linux操作系统环境下防火墙的使用建议．

This article describes the work progress of the Firewall under the Linux Operating System enviroment and it also describes the work progress of Packet Filtering in Firewall ,such as function and flow chart ,the work flow chart of the rule of Packet Filtering is proposed; at the same time , the pith function ip_fw_check（）of Packet Filtering is explained particularly ,whose function parameters ,return value and work process are analysed detailedly .The IPchains structure Ip_fw of the Firewall is also proposed, and in order to show the judgement for the chain structure of Firewall ,one ip_fw structure is take as an example. Be the above mentional describtion ,the whole progress of Firewall under the enviroment of Linux opreating system are described very clearly and how the firewall judge and control the data current under the environment is clearly proposed. At last,the suggestion for using the Firewall under the Linux operating System are also proposed.