This is the format for Iptables configuration file:

*<table-name>
:<chain-name> <chain-policy> [<packet-counter>:<byte-counter>]
rules ……
COMMIT


This is an example:

*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 -i eth0 -j ACCEPT
-A RH-Firewall-1-INPUT -i vmnet1 -j ACCEPT
-A RH-Firewall-1-INPUT -i vmnet8 -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 80 -j ACCEPT
-A RH-Firewall-1-INPUT -j REJECT –reject-with icmp-host-prohibited
COMMIT
*nat
:PREROUTING ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]
-A POSTROUTING -o ppp0 -j MASQUERADE
COMMIT

Each table is marked like *<table-name>, for example *filter. Then within each table we have the chain specifications and rules. A chain specification looks like :<chain-name> <chain-policy> [<packet-counter>:<byte-counter>]. The chain-name may be for example PREROUTING, the policy is described previously and can for example be ACCEPT. The packet-counter and byte-counters are the same counters as in the output from iptables -L -v. Finally, each table declaration ends in a COMMIT keyword. The COMMIT keywords tells us that at this point we should commit all rules currently in the pipeline to the kernel.