If you are setting up your Linux PC as a PPP server, you must compile in IP forwarding support. This is also necessary if you want to use Linux to link to LANs together or your LAN to the Internet.
If you are linking a LAN to the Internet (or linking together two LANs), you should be concerned about security. Adding support for IP fire walls to the kernel is probably a MUST!
You will also need this if you want to use IP masquerade to connect a LAN that uses any of the above mentioned 'unconnected' IP network numbers.
To enable IP Masquerade and IP fire walling, you MUST answer yes to the first question in the make config process:-
Prompt for development and/or incomplete code/drivers (CONFIG_EXPERIMENTAL)?
Whilst this may sound a bit off-putting to new users, many users are actively using the IP Masquerade and IP fire walling features of the Linux 2.0.x or 2.2.x kernels with no problems.
Once you have installed and rebooted your new kernel, you can start configuring and testing your PPP link(s).