# iptables

## 經由先前的簡易測試，我們針對ipv4設置iptables的過濾規則

### 清理規則

-F : Deleting (flushing) all the rules. 

-X : Delete chain. 

-t table\_name : Select table (called nat or mangle) and delete/flush rules. 

-P : Set the default policy (such as DROP, REJECT, or ACCEPT).

```
# Flush filter
IPTABLES=/sbin/iptables
$IPTABLES -F
$IPTABLES -X

echo "Flush mangle table ......"
echo
# Flush mangle
$IPTABLES -F -t mangle
$IPTABLES -t mangle -X


echo "Flush nat table ......"
echo
# Flush nat
$IPTABLES -F -t nat
$IPTABLES -t nat -X
###-----------------------------------------------------###
# 設定 filter table 的預設政策
###-----------------------------------------------------###
$IPTABLES -P INPUT ACCEPT
$IPTABLES -P OUTPUT ACCEPT
$IPTABLES -P FORWARD ACCEPT

```

IPTables中，主要有三張table，每張table內有專屬的chain，每個chain裡面有一系列的rule。

![圖片來源：http://www.thegeekstuff.com/2011/01/iptables-fundamentals/](/files/-M0L1yk8fbvX4HaELe4-)

所以，在進行規則規劃前，都應先清除所有的規則，保持乾淨

## 以前寫的shell

```
#!/bin/bash
#Author:kawsing
#Date:2012/11/27
#快速關閉防火牆，並回復預設值
ipt="/sbin/iptables"
#預設policies，全部ACCEPT
$ipt -t filter -P INPUT ACCEPT
$ipt -t filter -P FORWARD ACCEPT
$ipt -t filter -P OUTPUT ACCEPT
$ipt -t nat -P PREROUTING ACCEPT
$ipt -t nat -P OUTPUT ACCEPT
$ipt -t nat -P POSTROUTING ACCEPT
$ipt -t mangle -P INPUT ACCEPT
$ipt -t mangle -P OUTPUT ACCEPT
$ipt -t mangle -P FORWARD ACCEPT
$ipt -t mangle -P PREROUTING ACCEPT
$ipt -t mangle -P POSTROUTING ACCEPT

#計數器歸零
$ipt -t filter -Z
$ipt -t nat -Z
$ipt -t mangle -Z

#清除chain的規則
$ipt -t filter -F
$ipt -t nat -F
$ipt -t mangle -F
$ipt -t filter -X
$ipt -t nat -X
$ipt -t mangle -X
```


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