Linux IPTables Flush：删除/删除 RedHat 和 CentOS Linux 上的所有规则

在基于 Red Hat 的 Linux 上，iptables 带有某些默认规则。清理它们并从头开始是个好主意。

在我们开始学习如何使用 iptables 添加防火墙规则之前，了解如何清理所有现有的默认规则并从头开始一切会很有帮助。

IPTables 中的默认规则

如下图启动iptables防火墙。

# service iptables status
Firewall is stopped.

# service iptables start
Applying iptables firewall rules:                          [  OK  ]
Loading additional iptables modules: ip_conntrack_netbios_n[  OK  ]

可以看到下面的默认规则：iptables -> Filter Table -> RH-Firewall-1-INPUT Chain，如下图。您还可以使用 'iptables –list' 查看所有规则。

# service iptables status
Table: filter
Chain INPUT (policy ACCEPT)
num  target     prot opt source               destination
1    RH-Firewall-1-INPUT  all  --  0.0.0.0/0            0.0.0.0/0

Chain FORWARD (policy ACCEPT)
num  target     prot opt source               destination
1    RH-Firewall-1-INPUT  all  --  0.0.0.0/0            0.0.0.0/0

Chain OUTPUT (policy ACCEPT)
num  target     prot opt source               destination

Chain RH-Firewall-1-INPUT (2 references)
num  target     prot opt source               destination
1    ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0
2    ACCEPT     icmp --  0.0.0.0/0            0.0.0.0/0           icmp type 255
3    ACCEPT     esp  --  0.0.0.0/0            0.0.0.0/0
4    ACCEPT     ah   --  0.0.0.0/0            0.0.0.0/0
5    ACCEPT     udp  --  0.0.0.0/0            224.0.0.251         udp dpt:5353
6    ACCEPT     udp  --  0.0.0.0/0            0.0.0.0/0           udp dpt:631
7    ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0           tcp dpt:631
8    ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0           state RELATED,ESTABLISHED
9    ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0           state NEW tcp dpt:22
10   REJECT     all  --  0.0.0.0/0            0.0.0.0/0           reject-with icmp-host-prohibited

IPTables 规则存储在 /etc/sysconfig/iptables

请注意，iptables 规则存储在 /etc/sysconfig/iptables 文件中。如果您查看此文件，您将看到所有默认规则。

# cat /etc/sysconfig/iptables
# Firewall configuration written by system-config-securitylevel
# Manual customization of this file is not recommended.
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:RH-Firewall-1-INPUT - [0:0]
-A INPUT -j RH-Firewall-1-INPUT
-A FORWARD -j RH-Firewall-1-INPUT
-A RH-Firewall-1-INPUT -i lo -j ACCEPT
-A RH-Firewall-1-INPUT -p icmp --icmp-type any -j ACCEPT
-A RH-Firewall-1-INPUT -p 50 -j ACCEPT
-A RH-Firewall-1-INPUT -p 51 -j ACCEPT
-A RH-Firewall-1-INPUT -p udp --dport 5353 -d 224.0.0.251 -j ACCEPT
-A RH-Firewall-1-INPUT -p udp -m udp --dport 631 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m tcp --dport 631 -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 22 -j ACCEPT
-A RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited
COMMIT

暂时删除所有防火墙规则

使用 'iptables –flush' 选项暂时删除所有规则。

# iptables --flush

# iptables --list
Chain INPUT (policy ACCEPT)
target     prot opt source               destination

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

Chain RH-Firewall-1-INPUT (0 references)
target     prot opt source               destination

在“iptables –flush”之后，如果您重新启动 iptables，您将再次看到所有默认规则。所以，–flush 只是暂时的。

# service iptables stop

# service iptables start

# iptables --list

永久删除所有默认防火墙规则

在删除所有防火墙规则之前，您将在 /etc/sysconfig/iptables 文件中看到以下内容。

# cat  /etc/sysconfig/iptables
# Firewall configuration written by system-config-securitylevel
# Manual customization of this file is not recommended.
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:RH-Firewall-1-INPUT - [0:0]
-A INPUT -j RH-Firewall-1-INPUT
-A FORWARD -j RH-Firewall-1-INPUT
-A RH-Firewall-1-INPUT -i lo -j ACCEPT
-A RH-Firewall-1-INPUT -p icmp --icmp-type any -j ACCEPT
-A RH-Firewall-1-INPUT -p 50 -j ACCEPT
-A RH-Firewall-1-INPUT -p 51 -j ACCEPT
-A RH-Firewall-1-INPUT -p udp --dport 5353 -d 224.0.0.251 -j ACCEPT
-A RH-Firewall-1-INPUT -p udp -m udp --dport 631 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m tcp --dport 631 -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 22 -j ACCEPT
-A RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited
COMMIT

First, flush all these rules temporarily, as we discussed above.

首先，正如我们上面讨论的那样，暂时刷新所有这些规则。

# iptables --flush

接下来，使用“service iptables save”将当前的 iptables（它是空的，因为我们刚刚刷新它）保存到 /etc/sysconfig/iptables 文件以供永久使用

# service iptables save
Saving firewall rules to /etc/sysconfig/iptables:          [  OK  ]

最后，查看 /etc/sysconfig/iptables 以确保没有规则。

# cat  /etc/sysconfig/iptables
# Generated by iptables-save v1.3.5 on Thu Oct 28 08:44:01 2020
*filter
:INPUT ACCEPT [102:7668]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [78:8560]
COMMIT
# Completed on Thu Oct 28 08:44:01 2020

现在，如果您停止并启动 iptables，您将不再看到默认规则。因此，请记住执行“service iptables save”以使“iptables –flush”永久化。

# service iptables stop

# service iptables start

# iptables --list

现在您了解了iptables的基础知识，以及如何清理所有现有规则以从头开始。