IPTABLES, Custom IP Chains in Linux

Creating a custom IP Chain, adding rules to that and creating a rule which would bring the Custom Chain into play:

1. Create a New Rule:

[root@rhel5 ~]# iptables -N MYCHAIN

2. Add a rule to that chain eg. to disallow an IP (192.168.1.10) from accessing the SMTP port (25) on (192.168.1.20):

[root@rhel5 ~]# iptables -A MYCHAIN -s 192.168.1.10 -d 172.168.1.20 -p tcp --dport 25 -j REJECT

(The destination IP is an alias to the network interface eth0, eg. eth0:1)

3. Creating a rule in the default INPUT chain which would jump to the custom rule whenever any request comes on the eth+ interface:

[root@rhel5 ~]# iptables -A INPUT -i eth+ -j MYCHAIN

4. Save the iptables rules:

[root@rhel5 ~]# service iptables save

5. Restart the iptables service

[root@rhel5 ~]# service iptables restart

6. To list all the rules;

[root@rhel5 ~]# iptables -L