IP Forwarding and iptables configuration

Forwarding must be enabled
root@raspbx:~# cat /proc/sys/net/ipv4/ip_forward
0
root@raspbx:~# sysctl -w net.ipv4.ip_forward=1
net.ipv4.ip_forward = 1
root@raspbx:~# cat /proc/sys/net/ipv4/ip_forward
1
root@raspbx:~#
Routing and Masquerading
iptables --table nat --append POSTROUTING -o ppp0 -j MASQUERADE
iptables --append FORWARD -i eth0 -j ACCEPT

Forwarding traffic from one port to another machine and port

1. iptables -t nat -A PREROUTING -p tcp --dport 1111 -j DNAT --to-destination 2.2.2.2:1111
   

and finally, we ask IPtables to masquerade:

iptables -t nat -A POSTROUTING -j MASQUERADE