MPPE support is required for MSCHAPv2. Depending on the kernel version, you may or may not require to perform this step. Kernel version 2.6.15 or above has MPPE built-in. If you are using the latest FC4 2.6.15 kernel, you can go to step 7 now. If you are using an older kernel which does not support MPPE, you will have to add this feature to it.
To test if your kernel supports MPPE:
[root@pptp ~]# modprobe ppp-compress-18 && echo ok
If it returns an "ok", you can safely skip this step and move to step 7. If you see "FATAL: Module ppp_mppe not found.", install MPPE support as described in the following procedure:
Download the MPPE module builder in rpm format from here. The required RPMs are::
dkms-2.0.6-1.noarch.rpm kernel_ppp_mppe-1.0.2-3dkms.noarch.rpm
Install them with command "rpm -ivh".
[root@pptp ~]# rpm -ivh dkms-2.0.6-1.noarch.rpm [root@pptp ~]# rpm -ivh kernel_ppp_mppe-1.0.2-3dkms.noarch.rpm
If you upgrade your kernel to 2.6.13 or above, kernel_ppp_mppe version 1.0.2 or above must be used. Otherwise, the pptp tunnel will not connect and you will see error message "This system lacks kernel support for PPP." in /var/log/messages.
If you upgrade your kernel after installing dkms, thanks to the dkms_autoinstaller service, you will not have to worry about the dkms kernel module. dkms_autoinstaller runs on every bootup. It checks the dkms module to ensure it match the kernel version. If a mismatch is found, it will create a proper one for the boot kernel.
For dkms_autoinstaller to work, you will need the correct kernel-devel version installed in your system. It is always a good idea to install the kernel-devel rpm alongside with your new kernel.
FC4 comes with ppp-2.4.2-7. It is required to be upgraded to a patched version which supports MPPE. The patched version can be found in here. Download the rpm for FC4. At the time of writing, the latest version is 2.4.3-5. Get the FC4 rpm:
ppp-2.4.3-5.fc4.i386.rpm
Upgrade the ppp with the downloaded version:
[root@pptp ~]# rpm -Uvh ppp-2.4.3-5.fc4.i386.rpm
Note: If you are a Gentoo user, and are using kernel v2.6.15, the ppp-2.4.3-5 does NOT work because of MPPC. You may find more information from here.
In the same page download the pptpd rpm, pptpd-1.3.1-0.i386.rpm, and install it.
[root@pptp ~]# rpm -ivh pptpd-1.3.1-0.i386.rpm
Note: pptpd-1.3.1 is an experimental version. The stable version is 1.3.0. Both versions work fine for me. It is up to you to choose which one to use.