[pptp-server] pptp-client maxes out cpu connecting to pptpd

[Giulio Orsero]

Problem:
pptp-client maxes out cpu if the pptpd server uses its real ip as
"localip" (I'm doing tests of pptp-linux<->pptpd connection on the local
lan).

Setup (server and client have identical software installed):
linux 2.2.16-22, ppp-2.3.11 (mppe), pptpd 1.1.2.
I tried pptp 1.0.2 available here
http://cag.lcs.mit.edu/~cananian/Projects/PPTP/
and even the one with some more patches available here
http://www.scooter.cx/alpha/pptp.html


The pptpd server works ok with win9x clients.

I connect with
pptp <server-name> name <name> mppe-128 mppe-stateless lock noauth

Server has the following parameters:
localip <its real ip>
===
lock
proxyarp
auth
+chapms-v2
mppe-128
mppe-stateless
ms-wins ip.address
ms-wins same.ip.address
require-mppe
require-mppe-stateless
ipparam pptp
===

If I try to connect to the server with the linux pptp client, I get a
successful connection (mppe, 128), but the pptp client process uses 99%
cpu. 

After just a few seconds
 5518 ttyp0    S      0:00 pptp: call manager for 192.168.1.10
 5519 ttyp0    R      0:14 pptp: GRE-to-PPP gateway on /dev/ttyp6
 5520 ttyp6    S      0:00 /usr/sbin/pppd /dev/ttyp6 38400 name <name>
mppe-128

5519 keeps using 99% cpu
Moreover, I cannot ping the server.
Is this known problem/is there a solution?

If I change the pptpd "localip" parameter, setting a different ip then
the problem goes away and I can ping both the real server ip and the
pptpd one.

ie:
server eth0 is 192.168.1.1
client eth0 is 192.168.1.2
if "localip" is 192.168.1.1 I have the problem, if "localip" is
192.168.1.3 all is ok.


Thanks.

-- 
giulioo at pobox.com