Port Forwarding in CentOS Using Iptables

Port forwarding could be useful when you do not want to you client to put a port nuimber after you web address. In my case I forward port 8080 to 80. 1. check if IP forwarding is enabled:

/sbin/sysctl net.ipv4.ip_forward

if return net.ipv4.ip_forward = 1 then it is enabled. if not edit /etc/sysctl.conf and set net.ipv4.ip_forward = 1.
2. COnfigure and restart iptables

/sbin/sysctl -p /etc/sysctl.conf
/sbin/service iptables restart

3. Adding IP forwarding rules to IpTables

/sbin/iptables -I FORWARD 1 -m state --state ESTABLISHED,RELATED -j ACCEPT
/sbin/iptables -I FORWARD 1 -p tcp --dport 80 -j ACCEPT
/sbin/iptables -t nat -A PREROUTING -p tcp --dport 80 -j DNAT --to-destination 10.0.1.1:8080
/sbin/iptables -t nat -A POSTROUTING -j MASQUERADE
/sbin/service iptables save
/sbin/service iptables restart

The content of /etc/sysconfig/iptables files looks like:

# Generated by iptables-save v1.3.5 on Fri Mar 8 10:27:21 2013
*nat
:PREROUTING ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
-A PREROUTING -p tcp -m tcp --dport 80 -j DNAT --to-destination 10.0.1.1:8080
-A POSTROUTING -j MASQUERADE
COMMIT
# Completed on Fri Mar 8 10:27:21 2013
# Generated by iptables-save v1.3.5 on Fri Mar 8 10:27:21 2013
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [234:26336]
:RH-Firewall-1-INPUT - [0:0]
-A INPUT -j RH-Firewall-1-INPUT
-A FORWARD -p tcp -m tcp --dport 80 -j ACCEPT
-A FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT
-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 -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 -j REJECT --reject-with icmp-host-prohibited
COMMIT