[CentOS] centos7: pptpd vpn problem: mppe_decompress[0]: FLUSHED bit not set in stateless mode!

Mon Mar 26 11:03:11 UTC 2018
Dario Lesca <d.lesca at solinos.it>

I try to setup a PPTP VPN server on Centos 7 and from client a router
Vodafone Station (Firmware
On c7 I have install this:
[root at s-virt tmp]# rpm -q pptpd ppppptpd-1.4.0-2.el7.x86_64ppp-2.4.5-
and setup all file and firewall like howto say.This now is my config:
109/etc/ppp/options.pptpd:name pptpd/etc/ppp/options.pptpd:refuse-
128/etc/ppp/options.pptpd:lock/etc/ppp/options.pptpd:nobsdcomp /etc/ppp
pd:nologfd/etc/ppp/chap-secrets:myuser      pptpd   mypass            *

The connection from V.S. router to my c7 server work:mar 26 12:50:28 s-
virt.ansaldi.loc pptpd[26782]: CTRL: Client x.x.x.x control connection
startedmar 26 12:50:28 s-virt.ansaldi.loc pptpd[26782]: CTRL: Starting
call (launching pppd, opening GRE)mar 26 12:50:28 s-virt.ansaldi.loc
pppd[26783]: Plugin /usr/lib64/pptpd/pptpd-logwtmp.so loaded.mar 26
12:50:28 s-virt.ansaldi.loc pppd[26783]: pppd 2.4.5 started by root,
uid 0mar 26 12:50:28 s-virt.ansaldi.loc pppd[26783]: Using interface
ppp0mar 26 12:50:28 s-virt.ansaldi.loc pppd[26783]: Connect: ppp0 <-->
/dev/pts/19mar 26 12:50:28 s-virt.ansaldi.loc NetworkManager[1026]:
<info>  [1522061428.6946] manager: (ppp0): new Generic device
(/org/freedesktop/NetworkManager/Devices/40)mar 26 12:50:28 s-
virt.ansaldi.loc pppd[26783]: peer from calling number x.x.x.x
authorizedmar 26 12:50:31 s-virt.ansaldi.loc pppd[26783]: MPPE 128-bit
stateless compression enabledmar 26 12:50:34 s-virt.ansaldi.loc
pppd[26783]: local  IP address 26 12:50:34 s-
virt.ansaldi.loc pppd[26783]: remote IP address
But when I try to connect from a client (through the V. S. router) to
my server via VPN, or ping it, on 4 ping only two work, and into log of
server I see this error when the ping fail.
> mar 26 12:00:50 s-virt.ansaldi.loc kernel: mppe_decompress[0]:
> FLUSHED bit not set in stateless mode!

Someone have some suggest to resolve this problem ?
Many thanks

Dario Lesca
(inviato dal mio Linux Fedora 27 Workstation)