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When pppd is running as installed, but sometimes pppd does not work and showing warning message - discarding bogus packet: pppd is dropping its packet intentionally, so VPN is actually not working from that time. The workaround I can do is just disconnect the VPN and reconnect.

I just checked system progress by

ps aux --sort | grep ppp


and verified pppd is correctly working as planned as below:

root      3185  0.0  0.0  80708  1632 ?        Ss   Apr22   0:00 pppd call linuxconfig
root      3186  0.0  0.0  13180  1380 ?        S    Apr22   0:17 pptp u************.com --nolaunchpppd
root      3203  0.0  0.0  12812   628 ?        S    Apr22   0:00 pptp u************.com --nolaunchpppd


I also checked /var/log/messages and found below error messages - it looks like something is coming, but ignoring its packet by pptpd.

Apr 23 08:32:21 ***** pptp[3186]: anon warn[decaps_gre:pptp_gre.c:439]: discarding bogus packet 118939 (expecting 99092)
Apr 23 08:32:23 ***** pptp[3186]: anon warn[decaps_gre:pptp_gre.c:439]: discarding bogus packet 118940 (expecting 99092)
Apr 23 08:32:23 ***** pptp[3186]: anon warn[decaps_gre:pptp_gre.c:439]: discarding bogus packet 118941 (expecting 99092)
Apr 23 08:32:24 ***** pptp[3186]: anon warn[decaps_gre:pptp_gre.c:439]: discarding bogus packet 118942 (expecting 99092)
Apr 23 08:32:26 ***** pptp[3186]: anon warn[decaps_gre:pptp_gre.c:439]: discarding bogus packet 118943 (expecting 99092)
Apr 23 08:32:28 ***** pptp[3186]: anon warn[decaps_gre:pptp_gre.c:439]: discarding bogus packet 118944 (expecting 99092)
Apr 23 08:32:29 ***** pptp[3186]: anon warn[decaps_gre:pptp_gre.c:439]: discarding bogus packet 118945 (expecting 99092)
Apr 23 08:32:29 ***** pptp[3186]: anon warn[decaps_gre:pptp_gre.c:439]: discarding bogus packet 118946 (expecting 99092)
Apr 23 08:32:31 ***** pptp[3186]: anon warn[decaps_gre:pptp_gre.c:439]: discarding bogus packet 118947 (expecting 99092)
Apr 23 08:32:33 ***** pptp[3186]: anon warn[decaps_gre:pptp_gre.c:439]: discarding bogus packet 118948 (expecting 99092)
Apr 23 08:32:36 ***** pptp[3186]: anon warn[decaps_gre:pptp_gre.c:439]: discarding bogus packet 118949 (expecting 99092)
Apr 23 08:32:40 ***** pptp[3186]: anon warn[decaps_gre:pptp_gre.c:439]: discarding bogus packet 118950 (expecting 99092)

The PPTP setting I use is as following:

vi /etc/ppp/options.pptp
###############################################################################
# $Id: options.pptp,v 1.3 2006/03/26 23:11:05 quozl Exp $
#
# Sample PPTP PPP options file /etc/ppp/options.pptp
# Options used by PPP when a connection is made by a PPTP client.
# This file can be referred to by an /etc/ppp/peers file for the tunnel.
# Changes are effective on the next connection.  See "man pppd".
#
# You are expected to change this file to suit your system.  As
# packaged, it requires PPP 2.4.2 or later from http://ppp.samba.org/
# and the kernel MPPE module available from the CVS repository also on
# http://ppp.samba.org/, which is packaged for DKMS as kernel_ppp_mppe.
###############################################################################

# Lock the port
lock

# Authentication
# We don't need the tunnel server to authenticate itself
noauth

# We won't do PAP, EAP, CHAP, or MSCHAP, but we will accept MSCHAP-V2
# (you may need to remove these refusals if the server is not using MPPE)
refuse-pap
refuse-eap
refuse-chap
refuse-mschap

# Compression
# Turn off compression protocols we know won't be used
nobsdcomp
nodeflate

# Encryption
# (There have been multiple versions of PPP with encryption support,
# choose which of the following sections you will use.  Note that MPPE
# requires the use of MSCHAP-V2 during authentication)
#
# Note that using PPTP with MPPE and MSCHAP-V2 should be considered
# insecure:
# http://marc.info/?l=pptpclient-devel&m=134372640219039&w=2
# https://github.com/moxie0/chapcrack/blob/master/README.md
# http://technet.microsoft.com/en-us/security/advisory/2743314

# http://ppp.samba.org/ the PPP project version of PPP by Paul Mackarras
# ppp-2.4.2 or later with MPPE only, kernel module ppp_mppe.o
# If the kernel is booted in FIPS mode (fips=1), the ppp_mppe.ko module
# is not allowed and PPTP-MPPE is not available.
# {{{
# Require MPPE 128-bit encryption
# require-mppe-128
# }}}

# http://mppe-mppc.alphacron.de/ fork from PPP project by Jan Dubiec
# ppp-2.4.2 or later with MPPE and MPPC, kernel module ppp_mppe_mppc.o
# {{{
# Require MPPE 128-bit encryption
# mppe required,stateless
# }}}

I haven't solved that issue at the moment, and going to update this page when I resolve it.

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