10.6. Does FreeBSD support NAT or Masquerading

If you have a local subnet (one or more local machines), but have been allocated only a single IP number from your Internet provider (or even if you receive a dynamic IP number), you may want to look at the natd program. Natd allows you to connect an entire subnet to the internet using only a single IP number.

The ppp program has similar functionality built in via the -alias switch. The alias library is used in both cases.