Note that these modules cannot be loaded using the kerneld daemon. Each of the modules takes an argument specifying what ports it will listen on. The ports you need to specify depend on the protocol. The netfilter package includes modules that perform similar functions. If you've already read the firewall and accounting chapters, it probably comes as no surprise that the ipfwadm , ipchains , and iptables commands are used to configure the IP masquerade rules as well.
Masquerade rules are a special class of filtering rule.
You can masquerade only datagrams that are received on one interface that will be routed to another interface. To configure a masquerade rule you construct a rule very similar to a firewall forwarding rule, but with special options that tell the kernel to masquerade the datagram. Let's look at an example. A computing science student at Groucho Marx University has a number of computers at home internetworked onto a small Ethernet-based local area network. She has chosen to use one of the reserved private Internet network addresses for her network.