3.3. IP Aliasing

All of the configuration steps described thus far are relevant to any FreeBSD system which will be used to connect to an ISP via dial-up connection.

If your sole objective in reading this guide is to connect your FreeBSD box to the Internet using dial-out ppp you can proceed to Chapter 5.

One very attractive feature of the PPP program in on-demand mode is its ability to route IP traffic between other systems on the Local Area Network automatically. This feature is known by various names, "IP Aliasing", "Network Address Translation", "Address Masquerading" or "Transparent Proxying".

Regardless of the terminology used, this mode is not, however, automatic. If the PPP program is started normally then the program will not forward packets between LAN interface(s) and the dial-out connection. In effect, only the FreeBSD system is connected to the ISP; other workstations cannot "share" the same connection.

For example, if the program is started with either of the following command lines:

# ppp interactive (Interactive mode)

or

# ppp -auto demand (Dial-on-Demand mode)

then the system will function as an Internet-connected workstation only for the FreeBSD box.

To start the PPP program as a gateway between LAN resources and the Internet, one of the following command lines would be used instead:

# ppp -alias interactive (Interactive mode)

or

# ppp -auto -alias demand (Dial-on-Demand mode)

You can alternatively use the command ``alias enable yes'' in your ppp configuration file (refer to the man page for details).

Keep this in mind if you intend to proceed with Chapter 4.