Linux IPTables Port Forwarding

Port forwarding is very simple to do with iptables in a UNIX operating system. This work like  gateway operation. In UNIX kernels port forwarding can be done by  packet filter rules . Port forwarding also called  port mapping  usually refers to the network address translator  (NAT).

Iptables Commands

#iptables -L  - To List all the rule

#iptables -F  -to clear or flush the rule

In order to NAT or forward  request to other server , you need to make sure that the kernel is set to allow forwarding:

check the file /proc/sys/net/ipv4/ip_forward inside this file 1 should be there if it is 0 then run the below command.

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

Example Scenario  

Source IP 192.168.0.1 Port 1236

Destination IP 192.168.0.10 on port 6666

In My Scenario  we will connect server  192.168.0.1 on port 1236 and it should forward  to server 192.168.0.10 on port 6666

So here is the command syntax

#iptables -t nat -A  PREROUTING -p tcp -d 192.168.0.1 --dport 1236 -j DNAT --to 192.168.0.10:6666

#iptables -t nat  -A POSTROUTING -j MASQUERADE

once you execute above routing table and try to connect  server  192.168.0.1 on port 1236  it will connect  192.168.0.10 on port 6666

To Check the above rule you can use below command iptables -L will not show the tables

#iptables -t nat -vnL