ubuntu系统:

apt-get install iptables #如果默认没有安装，请运行此命令安装防火墙

# whereis iptables #查看系统是否安装防火墙可以看到:
iptables: /sbin/iptables /usr/share/iptables /usr/share/man/man8/iptables.8.gz #表示已经安装iptables
apt-get install iptables #如果默认没有安装，请运行此命令安装防火墙

# iptables -L #查看防火墙配置信息，显示如下:
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

# vi /etc/iptables.rules

添加以下内容(备注:80是指web服务器端口,3306是指MySQL数据库链接端口,22是指SSH远程管理端口.)
*filter
:INPUT DROP [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:syn-flood - [0:0]
-A INPUT -i lo -j ACCEPT
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A INPUT -p tcp -m state --state NEW -m tcp --dport 22 -j ACCEPT
-A INPUT -p tcp -m state --state NEW -m tcp --dport 80 -j ACCEPT
-A INPUT -p tcp -m state --state NEW -m tcp --dport 443 -j ACCEPT
-A INPUT -p icmp -m limit --limit 100/sec --limit-burst 100 -j ACCEPT
-A INPUT -p icmp -m limit --limit 1/s --limit-burst 10 -j ACCEPT
-A INPUT -p tcp -m tcp --tcp-flags FIN,SYN,RST,ACK SYN -j syn-flood
-A INPUT -j REJECT --reject-with icmp-host-prohibited
-A syn-flood -p tcp -m limit --limit 3/sec --limit-burst 6 -j RETURN
-A syn-flood -j REJECT --reject-with icmp-port-unreachable
COMMIT

# iptables-restore < /etc/iptables.rules #使防火墙规则生效

# vi /etc/network/if-pre-up.d/iptables #创建文件，添加以下内容，使防火墙开机启动
#!/bin/bash
iptables-restore < /etc/iptables.rules

# chmod +x /etc/network/if-pre-up.d/iptables #添加执行权限

# iptables -L -n查看规则是否生效.

eg.

# Generated by iptables-save v1.4.21 on Sat Aug 11 23:44:51 2018
*filter
:INPUT DROP [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [3122:409937]
:syn-flood - [0:0]
-A INPUT -i lo -j ACCEPT
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A INPUT -p tcp -m tcp --dport 21 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 20 -j ACCEPT
#-A INPUT -s 10.42.1.103 -p tcp -m tcp --dport 22 -j REJECT
-A INPUT -s 10.42.1.0/24 -p tcp -m tcp --dport 22 -j ACCEPT
#-A INPUT -p tcp -m state --state NEW -m tcp --dport 22 -j ACCEPT
-A INPUT -p tcp -m state --state NEW -m tcp --dport 80 -j ACCEPT
-A INPUT -p tcp -m state --state NEW -m tcp --dport 443 -j ACCEPT
-A INPUT -s 10.42.1.0/24 -p tcp -m tcp --dport 3306 -j ACCEPT
#-A INPUT -p tcp -m state --state NEW -m tcp --dport 3306 -j ACCEPT
-A INPUT -p icmp -m limit --limit 100/sec --limit-burst 100 -j ACCEPT
-A INPUT -p icmp -m limit --limit 1/sec --limit-burst 10 -j ACCEPT
-A INPUT -p tcp -m tcp --tcp-flags FIN,SYN,RST,ACK SYN -j syn-flood
-A INPUT -j REJECT --reject-with icmp-host-prohibited

-A syn-flood -p tcp -m limit --limit 3/sec --limit-burst 6 -j RETURN
-A syn-flood -j REJECT --reject-with icmp-port-unreachable
COMMIT
# Completed on Sat Aug 11 23:44:51 2018
# Generated by iptables-save v1.4.21 on Sat Aug 11 23:44:51 2018
*nat
:PREROUTING ACCEPT [2177:722593]
:INPUT ACCEPT [464:157009]
:OUTPUT ACCEPT [1877:120700]
:POSTROUTING ACCEPT [1877:120700]
COMMIT
# Completed on Sat Aug 11 23:44:51 2018

CentOS系统的iptables

查看防火墙规则列表: # iptables -L -n

设定预设规则:

#iptables -P INPUT DROP

注:如果你是远程SSH登陆的话,当你输入上述命令回车的时候就应该掉了.因为你没有设置任何规则.

怎么办,去本机操作呗!

# iptables -P OUTPUT ACCEPT

# iptables -P FORWARD DROP

上面的意思是,当超出了IPTABLES里filter表里的两个链规则(INPUT,FORWARD)时,不在这两个规则里的数据包怎么处理呢,那就是DROP(放弃).应该说这样配置是很安全的.我们要控制流入数据包