iptables

start & stop
service iptables start
service iptables stop

cat /etc/sysconfig/iptables

# Generated by iptables-save v1.3.5 on Thu Aug 21 15:51:38 2008
*filter
:INPUT ACCEPT [9:1126]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [169:26842]
: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 -m icmp --icmp-type any -j ACCEPT
-A RH-Firewall-1-INPUT -p esp -j ACCEPT
-A RH-Firewall-1-INPUT -p ah -j ACCEPT
-A RH-Firewall-1-INPUT -d 224.0.0.251 -p udp -m udp --dport 5353 -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 RELATED,ESTABLISHED -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 22 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 80 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 8000 -j ACCEPT
-A RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited
COMMIT
# Completed on Thu Aug 21 15:51:38 2008

iptables -L -n

iptables -D RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited
iptables -A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 8000 -j ACCEPT

usage of iptables