[pptp-server] MPPE encryption on pptpd

[Steve Rhodes]

I am having a problem using the mppe encryption.  Whenever I attempt to
send data over the pptp connection, the transmission fails, and a the
/var/log/messages entry reads "Unsupported protocol (0xZZZZ) received",
where (0xZZZZ) is some random hex number.  I can find these numbers
buried within the GRE encapsulated packets, but I'll be darned if I can
figure out what they mean.

I have tried several configurations of kernels, Stock RedHat 5.2
(2.0.36-0.7), 2.2.4 and 2.2.9.  I am always using the 2.3.8 pppd with
the ppp-2.3.8-mppe-others-norc4_TH7.diff patch.  I am using
SSLeay-0.6.6b.

The connection works flawlessly without any encryption applied, and I
can successfully connect and transmit with just encrypted password set.
Only when I specify data encryption required on the client, the
connection completes, but no data will transmit.  I have tried turning
off IP header compression and default gateway selections to no avail.

The only thing I have found where I differ from the instructions in the
HOWTO is that I have to manually  copy the rc4.h and rc4_enc.c files to
the linux source tree to successfully compile the modules.  I am
assuming this is an oversight on the instructions.

Any suggestions to get me pointed in the right direction would be
greatly appreciated.

Regards,

Steve Rhodes