iptables经典入门教程

iptables的组成

iptables由五个表table和五个链chain以及一些规则组成

五个表table:filter、nat、mangle、raw、security

filter表:过滤规则表,根据预定义的规则过滤符合条件的数据包
nat表:network address translation 地址转换规则表
mangle:修改数据标记位规则表
raw:关闭启用的连接跟踪机制,加快封包穿越防火墙速度
security:用于强制访问控制(MAC)网络规则,由Linux安全模块(如SELinux)实现

优先级由高到低的顺序为:

security -->raw-->mangle-->nat-->filter

五个内置链chain:

INPUT,OUTPUT,FORWARD,PREROUTING,POSTROUTING

链 chain:

  • 内置链:每个内置链对应于一个钩子函数
  • 自定义链:用于对内置链进行扩展或补充,可实现更灵活的规则组织管理机制;只有Hook钩子调用自定义链时,才生效

表和链对应关系
iptables经典入门教程插图

数据包过滤匹配流程

iptables经典入门教程插图(1)

内核中数据包的传输过程

  • 当一个数据包进入网卡时,数据包首先进入PREROUTING链,内核根据数据包目的IP判断是否需要转送出去
  • 如果数据包是进入本机的,数据包就会沿着图向下移动,到达INPUT链。数据包到达INPUT链后,任何进程都会收到它。本机上运行的程序可以发送数据包,这些数据包经过OUTPUT链,然后到达POSTROUTING链输出
  • 如果数据包是要转发出去的,且内核允许转发,数据包就会向右移动,经过FORWARD链,然后到达POSTROUTING链输出

范例:

root@centos8 ~]#iptables -vnL -t filter
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

[root@centos8 ~]#iptables -vnL -t nat
Chain PREROUTING (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain POSTROUTING (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination    

[root@centos8 ~]#iptables -vnL -t mangle
Chain PREROUTING (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain POSTROUTING (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination    

[root@centos8 ~]#iptables -vnL -t raw
Chain PREROUTING (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination   

[root@centos8 ~]#iptables -vnL -t security
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         
[root@centos8 ~]#

#CentOS 6 nat表不支持INPUT链
[root@centos6 ~]#iptables -vnL -t nat
Chain PREROUTING (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain POSTROUTING (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination 

2.5 netfilter 完整流程

iptables经典入门教程插图(2)

本文链接:http://www.yunweipai.com/35046.html

原创文章,作者:kepupublish,如若转载,请注明出处:https://blog.ytso.com/52530.html

(0)
上一篇 2021年8月6日
下一篇 2021年8月6日

相关推荐

发表回复

登录后才能评论