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

iptables -t nat -A PREROUTING -p tcp --dport 1111 -j DNAT --to-destination 2.2.2.2:1111
iptables -t nat -A PREROUTING -p tcp --dport 3723 -j DNAT --to-destination 10.0.0.100:3389

and finally, we ask IPtables to masquerade:

iptables -t nat -A POSTROUTING -j MASQUERADE

To delete an entry from the nat table

iptables -t nat -L -n --line-numbers<br

and find the line that matches the rules you want to deletes.
then

iptables -t nat -D

Reference - http://unix.stackexchange.com/questions/205867/viewing-all-iptables-rules

To get a complete presentation of the netfilter rules, you need
 
iptables -vL -t filter
iptables -vL -t nat
iptables -vL -t mangle
iptables -vL -t raw
iptables -vL -t security

iptables --table nat --list or in the short form:
iptables -t nat -L