NAT CONFIGURATION / INTERNET SHARING:

Scenario 1 (Nat Table, POSTROUTING Chain Implementation):

End Result: An Internet gateway server converting internal private IP
addreses in to public IP addres.
Server: linuxbox4 (192.168.0.14)
Internet Clients: 192.168.0.0/24 Network
Server Interface Connected to Internet: Modem / Linux interface name ppp0

Firewal Rules:

iptables -t nat -A POSTROUTING -s 192.168.0.0/24 -j MASQUERADE

OR

iptables -t nat -A POSTROUTING –o ppp0 -j MASQUERADE

Note: -i option cannot be used with POSTROUTING CHAIN

For net sharing purpose you must complete the Prerequisite as mentioned at the beginning of this document.