I just tried this, but got the same error...
This may be the issue - if ZeroTier changed or added a config that just took a moment to be acted upon (after the cache was cleared type of thing.)
VPN's are Extremely Finicky Beasts about initial settings.
@Aravisian , you are probably right. I just read that other people using ZT had problem with VPN after... well, I will stick with ZT for now, since it work OK and I'm able to stop it with the GUI interface.
I just created a log of all what happens (in syslog) when I try to connect to the VPN. Maybe theres a hint there. I anonymized the IP of the VPN with XXX.XXX.XXX.XXX.
I now doubt it will help, but hey! lets try.
Mar 31 00:59:52 Linux-iMac NetworkManager[897]: [1680238792.1544] audit: op="connection-activate" uuid="57991e14-861d-4399-bb81-5a550c747a48" name="WORK" pid=24532 uid=1000 result="success"
Mar 31 00:59:52 Linux-iMac NetworkManager[897]: [1680238792.1581] vpn-connection[0x556cbfa0e320,57991e14-861d-4399-bb81-5a550c747a48,"WORK",0]: Started the VPN service, PID 26710
Mar 31 00:59:52 Linux-iMac NetworkManager[897]: [1680238792.1661] vpn-connection[0x556cbfa0e320,57991e14-861d-4399-bb81-5a550c747a48,"WORK",0]: Saw the service appear; activating connection
Mar 31 00:59:52 Linux-iMac NetworkManager[897]: [1680238792.1814] vpn-connection[0x556cbfa0e320,57991e14-861d-4399-bb81-5a550c747a48,"WORK",0]: VPN plugin: state changed: starting (3)
Mar 31 00:59:52 Linux-iMac pppd[26714]: Plugin /usr/lib/pppd/2.4.7/nm-pptp-pppd-plugin.so loaded.
Mar 31 00:59:52 Linux-iMac NetworkManager[26714]: Plugin /usr/lib/pppd/2.4.7/nm-pptp-pppd-plugin.so loaded.
Mar 31 00:59:52 Linux-iMac pppd[26714]: pppd 2.4.7 started by root, uid 0
Mar 31 00:59:52 Linux-iMac pppd[26714]: Using interface ppp0
Mar 31 00:59:52 Linux-iMac NetworkManager[26714]: Using interface ppp0
Mar 31 00:59:52 Linux-iMac NetworkManager[26714]: Connect: ppp0 <--> /dev/pts/1
Mar 31 00:59:52 Linux-iMac pppd[26714]: Connect: ppp0 <--> /dev/pts/1
Mar 31 00:59:52 Linux-iMac pptp[26719]: nm-pptp-service-26710 log[main:pptp.c:353]: The synchronous pptp option is NOT activated
Mar 31 00:59:52 Linux-iMac NetworkManager[897]: [1680238792.1890] manager: (ppp0): new Ppp device (/org/freedesktop/NetworkManager/Devices/11)
Mar 31 00:59:52 Linux-iMac systemd-udevd[26718]: ethtool: autonegotiation is unset or enabled, the speed and duplex are not writable.
Mar 31 00:59:52 Linux-iMac pptp[26727]: nm-pptp-service-26710 log[ctrlp_rep:pptp_ctrl.c:258]: Sent control packet type is 1 'Start-Control-Connection-Request'
Mar 31 00:59:52 Linux-iMac pptp[26727]: nm-pptp-service-26710 log[ctrlp_disp:pptp_ctrl.c:781]: Received Start Control Connection Reply
Mar 31 00:59:52 Linux-iMac pptp[26727]: nm-pptp-service-26710 log[ctrlp_disp:pptp_ctrl.c:815]: Client connection established.
Mar 31 00:59:53 Linux-iMac pptp[26727]: nm-pptp-service-26710 log[ctrlp_rep:pptp_ctrl.c:258]: Sent control packet type is 7 'Outgoing-Call-Request'
Mar 31 00:59:53 Linux-iMac pptp[26727]: nm-pptp-service-26710 log[ctrlp_disp:pptp_ctrl.c:900]: Received Outgoing Call Reply.
Mar 31 00:59:53 Linux-iMac pptp[26727]: nm-pptp-service-26710 log[ctrlp_disp:pptp_ctrl.c:938]: Outgoing call established (call ID 41648, peer's call ID 61854).
Mar 31 00:59:53 Linux-iMac portmaster-start[914]: #033[33m230331 00:59:53.254 on/nfq/nfq:190 
WARN 363#033[0m nfqueue: failed to parse payload: Unable to decode PPPType 49185
Mar 31 00:59:55 Linux-iMac dbus-daemon[1367]: [session uid=1000 pid=1367] Activating via systemd: service name='org.freedesktop.Tracker1' unit='tracker-store.service' requested by ':1.1' (uid=1000 pid=1356 comm="/usr/libexec/tracker-miner-fs ")
Mar 31 00:59:55 Linux-iMac systemd[1345]: Starting Tracker metadata database store and lookup manager...
Mar 31 00:59:55 Linux-iMac dbus-daemon[1367]: [session uid=1000 pid=1367] Successfully activated service 'org.freedesktop.Tracker1'
Mar 31 00:59:55 Linux-iMac systemd[1345]: Started Tracker metadata database store and lookup manager.
Mar 31 00:59:55 Linux-iMac dbus-daemon[1367]: [session uid=1000 pid=1367] Activating via systemd: service name='org.freedesktop.Tracker1.Miner.Extract' unit='tracker-extract.service' requested by ':1.1' (uid=1000 pid=1356 comm="/usr/libexec/tracker-miner-fs ")
Mar 31 00:59:55 Linux-iMac systemd[1345]: Starting Tracker metadata extractor...
Mar 31 00:59:55 Linux-iMac tracker-extract[26736]: Set scheduler policy to SCHED_IDLE
Mar 31 00:59:55 Linux-iMac tracker-extract[26736]: Setting priority nice level to 19
Mar 31 00:59:55 Linux-iMac dbus-daemon[1367]: [session uid=1000 pid=1367] Successfully activated service 'org.freedesktop.Tracker1.Miner.Extract'
Mar 31 00:59:55 Linux-iMac systemd[1345]: Started Tracker metadata extractor.
Mar 31 00:59:56 Linux-iMac portmaster-start[914]: #033[33m230331 00:59:56.191 on/nfq/nfq:190 WARN 365#033[0m nfqueue: failed to parse payload: Unable to decode PPPType 49185
Mar 31 00:59:59 Linux-iMac portmaster-start[914]: #033[33m230331 00:59:59.194 on/nfq/nfq:190 WARN 367#033[0m nfqueue: failed to parse payload: Unable to decode PPPType 49185
Mar 31 01:00:02 Linux-iMac portmaster-start[914]: #033[33m230331 01:00:02.195 on/nfq/nfq:190 WARN 369#033[0m nfqueue: failed to parse payload: Unable to decode PPPType 49185
Mar 31 01:00:05 Linux-iMac portmaster-start[914]: #033[33m230331 01:00:05.198 on/nfq/nfq:190 WARN 371#033[0m nfqueue: failed to parse payload: Unable to decode PPPType 49185
Mar 31 01:00:08 Linux-iMac portmaster-start[914]: #033[33m230331 01:00:08.199 on/nfq/nfq:190 WARN 373#033[0m nfqueue: failed to parse payload: Unable to decode PPPType 49185
Mar 31 01:00:11 Linux-iMac portmaster-start[914]: #033[33m230331 01:00:11.202 on/nfq/nfq:190 WARN 375#033[0m nfqueue: failed to parse payload: Unable to decode PPPType 49185
Mar 31 01:00:14 Linux-iMac portmaster-start[914]: #033[33m230331 01:00:14.203 on/nfq/nfq:190 WARN 377#033[0m nfqueue: failed to parse payload: Unable to decode PPPType 49185
Mar 31 01:00:16 Linux-iMac rtkit-daemon[1370]: Supervising 1 threads of 1 processes of 1 users.
Mar 31 01:00:16 Linux-iMac rtkit-daemon[1370]: Supervising 1 threads of 1 processes of 1 users.
Mar 31 01:00:17 Linux-iMac portmaster-start[914]: #033[33m230331 01:00:17.204 on/nfq/nfq:190 WARN 379#033[0m nfqueue: failed to parse payload: Unable to decode PPPType 49185
Mar 31 01:00:20 Linux-iMac portmaster-start[914]: #033[33m230331 01:00:20.207 on/nfq/nfq:190 WARN 381#033[0m nfqueue: failed to parse payload: Unable to decode PPPType 49185
Mar 31 01:00:23 Linux-iMac pppd[26714]: LCP: timeout sending Config-Requests
Mar 31 01:00:23 Linux-iMac NetworkManager[26714]: LCP: timeout sending Config-Requests
Mar 31 01:00:23 Linux-iMac NetworkManager[26714]: Connection terminated.
Mar 31 01:00:23 Linux-iMac pppd[26714]: Connection terminated.
Mar 31 01:00:23 Linux-iMac NetworkManager[897]: [1680238823.2117] vpn-connection[0x556cbfa0e320,57991e14-861d-4399-bb81-5a550c747a48,"WORK",0]: VPN plugin: failed: connect-failed (1)
Mar 31 01:00:23 Linux-iMac NetworkManager[897]: [1680238823.2120] vpn-connection[0x556cbfa0e320,57991e14-861d-4399-bb81-5a550c747a48,"WORK",0]: VPN plugin: state changed: stopping (5)
Mar 31 01:00:23 Linux-iMac NetworkManager[897]: [1680238823.2158] vpn-connection[0x556cbfa0e320,57991e14-861d-4399-bb81-5a550c747a48,"WORK",0]: VPN service disappeared
Mar 31 01:00:23 Linux-iMac pptp[26719]: nm-pptp-service-26710 warn[decaps_hdlc:pptp_gre.c:226]: short read (-1): Input/output error
Mar 31 01:00:23 Linux-iMac pptp[26719]: nm-pptp-service-26710 warn[decaps_hdlc:pptp_gre.c:238]: pppd may have shutdown, see pppd log
Mar 31 01:00:23 Linux-iMac NetworkManager[26714]: Terminating on signal 15
Mar 31 01:00:23 Linux-iMac NetworkManager[26714]: Modem hangup
Mar 31 01:00:23 Linux-iMac NetworkManager[26714]: Child process /sbin/pptp XXX.XXX.XXX.XXX --nolaunchpppd --loglevel 0 --logstring nm-pptp-service-26710 (pid 26717) terminated with signal 15
Mar 31 01:00:23 Linux-iMac pppd[26714]: Terminating on signal 15
Mar 31 01:00:23 Linux-iMac pppd[26714]: Modem hangup
Mar 31 01:00:23 Linux-iMac pptp[26727]: nm-pptp-service-26710 log[callmgr_main:pptp_callmgr.c:245]: Closing connection (unhandled)
Mar 31 01:00:23 Linux-iMac pptp[26727]: nm-pptp-service-26710 log[ctrlp_rep:pptp_ctrl.c:258]: Sent control packet type is 12 'Call-Clear-Request'
Mar 31 01:00:23 Linux-iMac pptp[26727]: nm-pptp-service-26710 log[call_callback:pptp_callmgr.c:84]: Closing connection (call state)
Mar 31 01:00:23 Linux-iMac pppd[26714]: Child process /sbin/pptp XXX.XXX.XXX.XXX --nolaunchpppd --loglevel 0 --logstring nm-pptp-service-26710 (pid 26717) terminated with signal 15
Mar 31 01:00:23 Linux-iMac pppd[26714]: Exit.
I see some warnings, but the vast majority won't stop the VPN from working.
There is one that can prevent it:
But it does not look like it did because the logs after that still continue to show a running instance of the VPN.
Just in case, though:
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Good eye
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@337harvey, can I get a sanity check on sudo ethtool -s ppp0 speed 1000 duplex full autoneg off?
I placed ppp0 for the OP's name of their network adapter according to posted logs.
So... maybe adding synchronous line to/etc/ppp/options.pptp, saving and retrying?
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I put off because the error specifically stated that "autonegotiation is unset or enabled."
So I thought the off option would mean that the network interface will stop trying to automatically negotiate the link speed and duplex settings called by the speed and duplex options.
Anyway, I definitely don't want to hijack the thread - so that I could better view the preview, I accidentally out-of-hand, closed the prompt which mentioned I could message you with the above explanation and further check on my understanding. Didn't even know I could message someone to be honest, never tried.
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This one I tried, whitout success. I'm pretty sure I must change something manually in a config file.
I will check the other advises below this one, many answers during the night !
You're spot on. It's a configuration file that is misaligned with the endpoint:
- run the following on the configuration files.. I hope you are using dpkg so this will work after the next kernel update:
sudo dpkg-query -S [PATH-TO-CONFIG]
would be worthwhile to back that configuration file up somewhere with a .BAK extension and then restore it from package:
sudo dpkg --force-confmiss -i [PACKAGE-NAME]
from there you could use a diff to compare the two files in order to hopefully verify they are in line with your endpoint configuration.
I've done # sudo dpkg-query -S /etc/ppp/
I see that my ppp.options as changed a lot, BUT when I try to connect to the VPN, it act like it doesn't use this options file !
I will try to search where the "other" config is. Strange !
If I were using command line to connect to VPN, I think it would work like it was, knowing which file config it uses.
Sometimes graphical interface aren't the best option, you loose control.
If I show you a log from when it was working OK, can it help you ?
And in /etc/pptpd.conf it specify : option /etc/ppp/pptpd-options
I don't understand why it does not seem to use it. Maybe I need to reboot or restart a service.
I tried to create a command line connexion to the VPN, creating a file in /etc/ppp/peers following the instructions on this web page : How to setup PPTP VPN Connection on Ubuntu 20.x
When I try to connect via command line, I get this in syslog:
Mar 31 11:34:19 Linux-iMac NetworkManager[897]: [1680276859.9252] manager: (ppp0): new Ppp device (/org/freedesktop/NetworkManager/Devices/3830)
Mar 31 11:34:19 Linux-iMac systemd-udevd[43525]: ppp0: Failed to get link config: No such device
Mar 31 11:34:19 Linux-iMac pppd[43523]: using channel 3896
Mar 31 11:34:19 Linux-iMac pppd[43523]: Using interface ppp0
Mar 31 11:34:19 Linux-iMac pppd[43523]: Connect: ppp0 <--> /dev/pts/3
Mar 31 11:34:19 Linux-iMac pppd[43523]: Script xxx.xxx.xxx.xxx --nolaunchpppd --debug finished (pid 78265), status = 0x7f
Mar 31 11:34:19 Linux-iMac pppd[43523]: Modem hangup
Mar 31 11:34:19 Linux-iMac pppd[43523]: Connection terminated.
I don't understand why it refers to /org/freedesktop/NetworkManager/Devices/3830
Interesting :
I did a test with: telnet IP_VPN_SERVER 1723
It connect, obviously it's not usable, but still shows something.
Log of this in syslog :
Mar 31 14:02:49 Linux-iMac whoopsie[1989]: [14:02:49] offline
Mar 31 14:02:49 Linux-iMac dbus-daemon[891]: [system] Activating via systemd: service name='org.freedesktop.nm_dispatcher' unit='dbus-org.freedesktop.nm-dispatcher.service' requested by ':1.9' (uid=0 pid=892 comm="/usr/sbin/NetworkManager --no-daemon ")
Mar 31 14:02:49 Linux-iMac systemd[1]: Starting Network Manager Script Dispatcher Service...
Mar 31 14:02:49 Linux-iMac dbus-daemon[891]: [system] Successfully activated service 'org.freedesktop.nm_dispatcher'
Mar 31 14:02:49 Linux-iMac systemd[1]: Started Network Manager Script Dispatcher Service.
Mar 31 14:02:51 Linux-iMac NetworkManager[892]: [1680285771.7660] manager: NetworkManager state is now CONNECTED_GLOBAL
Mar 31 14:02:51 Linux-iMac whoopsie[1989]: [14:02:51] The default IPv4 route is: /org/freedesktop/NetworkManager/ActiveConnection/1
Mar 31 14:02:51 Linux-iMac whoopsie[1989]: [14:02:51] Not a paid data plan: /org/freedesktop/NetworkManager/ActiveConnection/1
Mar 31 14:02:51 Linux-iMac whoopsie[1989]: [14:02:51] Found usable connection: /org/freedesktop/NetworkManager/ActiveConnection/1
Mar 31 14:02:52 Linux-iMac whoopsie[1989]: [14:02:52] online
Mar 31 14:03:01 Linux-iMac systemd[1]: NetworkManager-dispatcher.service: Succeeded.
Hi @doalex,
Please understand that I have no prior experience with this process but I wanted to attempt to connect the dots and learn a few things about this as I go; please forgive me if any of this has already been asked/answered. At the very least I hope this prompts some 
for the more experienced Linux users so that they might be able to help you further.
To that end, I decided to try and throw something together based on your input and on the Ubuntu pptp manpage, as well as the Linux pppd manpage.
Are you trying to force your /etc/pptpd.conf file to use a specific options file? If so, maybe try to change the line in the .conf from
To: option /etc/ppp/options.pptp
This might tell the PPTP server to use the options.pptp file located in /etc/ppp/ as the configuration file for all PPTP connections.
Then: sudo service pptpd restart to restart service for changes to take effect.
From man pppd:
OPTIONS FILES
Options can be taken from files as well as the command line. Pppd
reads options from the files /etc/ppp/options, ~/.ppprc and
/etc/ppp/options.ttyname (in that order) before processing the options
on the command line. (In fact, the command-line options are scanned to
find the terminal name before the options.ttyname file is read.) In
forming the name of the options.ttyname file, the initial /dev/ is re‐
moved from the terminal name, and any remaining / characters are re‐
placed with dots.
An options file is parsed into a series of words, delimited by white‐
space. Whitespace can be included in a word by enclosing the word in
double-quotes ("). A backslash (\) quotes the following character. A
hash (#) starts a comment, which continues until the end of the line.
There is no restriction on using the file or call options within an op‐
tions file.
I think this is implied, but specific options files can be specified for individual connections in the /etc/ppp/peers location. These files are named after the connection they apply to, and contain options specific to that connection.
To force the PPTP client to always use /etc/ppp/options.pptp configuration/options file for your specific connection in the .../peers location, you can try to also add the line...
pty "pptp your_pptp_server_name --nolaunchpppd --debug --logstring PPTP"--logstring PPTPat the end is just the name that will be given to the log that will be created for debugging purposes.- The log file will be created in the same directory as the configuration file and will be named PPTP.log
...to your plain text peers file which I think you would find or create at /etc/ppp/peers/your_pptp_server_name
After adding the line noted above to the peers file, you might be able to start the VPN connection with: sudo pon your_vpn_server_name.
Your client might then use your server name you chose and prevent launching a local pppd process which would use the default configuration file in/etc/ppp/options; In theory, it would instead use the options file you created at /etc/ppp/options.pptp
When you use the command line, I read that it may also be possible to specify an options file explicitly using the -o command line option when starting the pppd process. But I can't verify that and I couldn't find mention of that when running man pppd in terminal.
call name
Read additional options from the file /etc/ppp/peers/name.
This file may contain privileged options, such as noauth,
even if pppd is not being run by root. The name string
may not begin with / or include .. as a pathname
component. The format of the options file is described
below.
Using an example format for a peers file, and with the above excerpt from Linux pppd manpage in mind:
# Name of the remote PPTP server
remote your_pptp_server_name
# Options to be used with the PPP connection
pty "pptp your_pptp_server_name --nolaunchpppd --debug --logstring PPTP"
# User authentication information
name my_username
password my_password
# Other options
noauth
nobsdcomp
nodeflate
-
You can have the
pppdprocess start a PPTP connection using a specifiedoptions.pptpfile and the settings in theyour_pptp_server_nameplain text file you created in the/etc/ppp/peers/...location:sudo pppd call your_pptp_server_name options /etc/ppp/options.pptpshould work if you configured the/etc/ppp/options.pptpfile with the necessary PPTP client options and replacedyour_pptp_server_namewith the correct name you specified in the options file.`
Hi @ajo001 !
I just tried your two suggestion, but I get the same error message as before.
Mar 31 23:55:37 Linux-iMac portmaster-start[910]: #033[33m230331 23:55:37.145 on/nfq/nfq:190 WARN 381#033[0m nfqueue: failed to parse payload: Unable to decode PPPType 49185
Thanks though for this very well elaborated answer !
Darn. I tried.
Out of curiosity, what was the PPTP.log file showing afterward? Anything you weren't expecting or already seeing?
There was no log file after... I just retried again to be 100 % sure.
I always open a second Terminal with tail -f /var/log/syslog to look live at what happens.
Oh ok. Sorry I've had a few tonight.
Maybe the PPTP.log file is only populated with data after a connection is successfully established and what's logged are data having to do with details of the traffic?
Lol I've given it my all, so hopefully a lightbulb appears over another experienced reader's head.
Sorry you still can't get it to work. 
🪿
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No problem @ajo001 ! Your help is greatly appreciated !
Passionate people about Linux are the best !
I don't know why there is no log produce, but syslog seems to be really the best place to look at. I didn't found a more complete log so far.
Since I still have Zerotier working to connect to my work, this isn't too tragic for me. If it wasn't I think I would reinstall Zorin Linux from scratch.
I really don't like to do this, loosing all my setup. I will look for a cloud solution to preserve my user home directory if I do that !
Thanks again !
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