CentOS 6
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iptables - Setting Example #3
2013/07/29
 
This is an Example of setting iptables on the Server below. 
         Internet
             |
       +----------+
-------|  Router  | -----------------------------------------------------------------------------
       +----------+                |                                   +----------+
             |                     |                          10.0.0.31|          |
    LAN(192.168.0.0/24)            |       LAN(10.0.0.0/24)  +---------| Backend1 |
             |               +----------+                    |         |          |  +----------+
             |  192.168.0.100|          |10.0.0.1            |         +----------+  |          |
-----------------------------|  Server  |--------------------|-----------------------|    PC    |
                         eth0|          |eth1                |         +----------+  |          |
                             +----------+                    |         |          |  +----------+
                                                             +---------| Backend2 |
                                                              10.0.0.32|          |
                                                                       +----------+
 
* DROP INPUT by Default
* ACCEPT OUTPUT by Default
* DROP FORWARD by Default
* ACCEPT Established Connection
* ACCEPT the Connection from loopback
* Forward the Packets to 80 on eth0 to the same port on Backend1
* Forward the Packets to 443 on eth0 to the same port on Backend2
* But DROP the Packets from 192.168.0.20
* ACCEPT Ping Connection for 5 times per a minites from internal network(10.0.0.0/24)
* ACCEPT SSH Connection from internal network(10.0.0.0/24)
* But DROP the Packets from 10.0.0.20
* ACCEPT Outgoing Packets through the Server from internal network(10.0.0.0/24) and translatte the source address
[1] Configure iptables
[root@dlp ~]#
vi iptables.sh 
#!/bin/bash

trust_host='10.0.0.0/24'
my_internal_ip='10.0.0.1'
my_external_ip='192.168.0.100'

listen_port_1='80'
backend_host_1='10.0.0.31'
backend_port_1='80'

listen_port_2='443'
backend_host_2='10.0.0.32'
backend_port_2='443'

echo 1 > /proc/sys/net/ipv4/ip_forward

/sbin/iptables -F
/sbin/iptables -t nat -F
/sbin/iptables -X

/sbin/iptables -P INPUT DROP
/sbin/iptables -P OUTPUT ACCEPT
/sbin/iptables -P FORWARD DROP

/sbin/iptables -A FORWARD -i eth1 -o eth0 -s $trust_host -j ACCEPT
/sbin/iptables -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT

/sbin/iptables -A FORWARD -s 192.168.0.20/32 -j DROP

/sbin/iptables -A FORWARD -p tcp --dst $backend_host_1 --dport $backend_port_1 -j ACCEPT
/sbin/iptables -A FORWARD -p tcp --dst $backend_host_2 --dport $backend_port_2 -j ACCEPT

/sbin/iptables -A INPUT -s 10.0.0.20/32 -j DROP

/sbin/iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
/sbin/iptables -A INPUT -s 127.0.0.1 -d 127.0.0.1 -j ACCEPT
/sbin/iptables -A INPUT -p icmp --icmp-type echo-request -s $trust_host \
-d $my_internal_ip -m limit --limit 1/m --limit-burst 5 -j ACCEPT
/sbin/iptables -A INPUT -p tcp -m state --state NEW -m tcp -s $trust_host \
-d $my_internal_ip --dport 22 -j ACCEPT

/sbin/iptables -t nat -A POSTROUTING -o eth0 -s $trust_host -j MASQUERADE

/sbin/iptables -t nat -A PREROUTING -p tcp --dst $my_external_ip --dport $listen_port_1 \
-j DNAT --to-destination $backend_host_1:$backend_port_1
/sbin/iptables -t nat -A PREROUTING -p tcp --dst $my_external_ip --dport $listen_port_2 \
-j DNAT --to-destination $backend_host_2:$backend_port_2

/etc/rc.d/init.d/iptables save
/etc/rc.d/init.d/iptables restart
[root@dlp ~]#
sh iptables.sh 

iptables: Saving firewall rules to /etc/sysconfig/iptables: [  OK  ]
iptables: Flushing firewall rules: [  OK  ]
iptables: Setting chains to policy ACCEPT: filter [  OK  ]
iptables: Unloading modules: [  OK  ]
iptables: Applying firewall rules: ip_tables: (C) 2000-2006 Netfilter Core Team
nf_conntrack version 0.5.0 (16384 buckets, 65536 max)
[  OK  ]
 
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