If your private network contains any vital information, think carefully in terms of SECURITY before implementing IP Masquerade. By default, IP MASQ becomes a GATEWAY for you to get onto the Internet, but it also can allow someone from the Internet to possibly get into your internal network.
Once you have IP MASQ functioning, it is HIGHLY recommended for the user to implement a STRONG IPFWADM/IPCHAINS firewall ruleset. Please see Section 6.4.1, Section 6.4.2 and Section 6.4.3 located below for more details.