This HOWTO assumes that you are using a Linux 1.2.x kernel with the PPP 2.1.2 software or Linux 1.3.X/2.0.x and PPP 2.2.
At the time of writing, the latest official version of PPP available for Linux is ppp-2.2f. The new version (ppp-2.3) is still in beta.
It is possible to use PPP 2.2.0 with kernel 1.2.13. This requires kernel patches. It is recommended that version 1.2.13 kernel users move up to ppp-2.2 as it includes several bug fixes and enhancements.
Also, you should particularly note that you cannot use the PPP 2.1.2 software with Linux kernel version 2.0.X.
Please note that this document does NOT cover problems arising from
the use of loadable modules for Linux kernel 2.0.x. Please see the
kerneld mini-HOWTO and the kernel/module 2.0.x documentation (in the
Linux 2.0.x source tree at /usr/src/linux/Documentation/...).
As this document is designed to assist new users, it is highly recommended that you use a version of the Linux kernel and the appropriate PPP version that are known to be stable together.