[pptp-devel] pptp connection dies in pptp-linux_1.9.* Works fine in pptp-linux_1.8.0-1

[dz <dz...@gm...>]

Dear developers,

After upgrading Ubuntu and hence pptp-linux package to version 
1.9.0+ds-2 my connection to an Asus home router-based pptp server dies 
after some minutes of active usage throwing in syslog a burst of dozens 
of messages "pptp[1320]: anon warn[pqueue_add:pqueue.c:151]: discarding 
duplicate packet nnnnn".
The connection is still on and ppp0 is shown among interfaces but no 
data goes through. Disconnecting and re-connecting resolves the issue 
just for few minutes of active use.
Uninstalling 1.9.0+ds-2 version of pptp-linux and installing instead 
pptp-linux_1.8.0-1_amd64.deb fixes the issue. Occasional single messages 
"discarding duplicate packet yyyyy" appear in the log with no impact to 
the connection. It stays on and works stable for days.
The problem is repeatable. I have installed a fresh formatted test 
system with ubuntu-18.04.1-server-amd64 OS and pptp-linux v.1.9.0+ds-2 
and the problem was there at once. Downgrading to 
pptp-linux_1.9.0+ds-1_amd64.deb does not solve the issue. Downgrading to 
v.1.8.0-1 does solve it at once.
Providing a relevant fragment of syslog for the reference:
---
Sep 19 23:12:18 dz-test pptp[1320]: anon warn[pqueue_add:pqueue.c:151]: 
discarding duplicate packet 58793
Sep 19 23:12:18 dz-test pptp[1320]: anon warn[pqueue_add:pqueue.c:151]: 
discarding duplicate packet 58797
Sep 19 23:12:18 dz-test pptp[1320]: anon warn[pqueue_add:pqueue.c:151]: 
discarding duplicate packet 58839
Sep 19 23:12:18 dz-test pptp[1320]: anon warn[pqueue_add:pqueue.c:151]: 
discarding duplicate packet 58840
Sep 19 23:12:18 dz-test pptp[1320]: anon warn[pqueue_add:pqueue.c:151]: 
discarding duplicate packet 58841
Sep 19 23:12:18 dz-test pptp[1320]: anon warn[pqueue_add:pqueue.c:151]: 
discarding duplicate packet 58842
...
Sep 19 23:12:18 dz-test pptp[1320]: anon warn[pqueue_add:pqueue.c:151]: 
discarding duplicate packet 58884
Sep 19 23:12:19 dz-test pptp[1320]: anon warn[pqueue_add:pqueue.c:151]: 
discarding duplicate packet 58885
...
Sep 19 23:12:19 dz-test pptp[1320]: anon warn[pqueue_add:pqueue.c:151]: 
discarding duplicate packet 58906
Sep 19 23:12:19 dz-test pptp[1320]: anon warn[pqueue_add:pqueue.c:151]: 
discarding duplicate packet 58907
Sep 19 23:12:19 dz-test pptp[1320]: anon warn[pqueue_add:pqueue.c:151]: 
discarding duplicate packet 58908
Sep 19 23:12:19 dz-test pptp[1320]: anon warn[pqueue_add:pqueue.c:151]: 
discarding duplicate packet 58909
Sep 19 23:12:19 dz-test pptp[1320]: anon warn[pqueue_add:pqueue.c:151]: 
discarding duplicate packet 58910
---
After the last line the connection became unusable.
I could provide more information if needed.
Please help to investigate the issue and possibly to resolve it in the 
next version of pptp-linux package.

With best regards, Dmitry