When pppd is running as installed, but the server running VPN client does not act anything with the warning message as discarding bogus packet, pppd is dropping its packet intentionally.
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)