I have setup a PPTP VPN connection to a service that successfully connects when I try to connect through the ISP that the service uses.
When I try under the ISP I use in my work (which is the ISP I must work under regularly) the connection fails after some seconds. edit: After a request in the comments I added more information below:
Ιουλ 12 08:44:22 Desktop pppd[8923]: pppd 2.4.7 started by root, uid 0
Ιουλ 12 08:44:22 Desktop pptp[8928]: nm-pptp-service-8913 log[main:pptp.c:353]: The synchronous pptp option is NOT activated
Ιουλ 12 08:44:22 Desktop pppd[8923]: Using interface ppp0
Ιουλ 12 08:44:22 Desktop NetworkManager[643]: <info> [] manager: (ppp0): new Ppp device (/org/freedesktop/NetworkManager/Devices/3)
Ιουλ 12 08:44:22 Desktop NetworkManager[8923]: Using interface ppp0
Ιουλ 12 08:44:22 Desktop NetworkManager[8923]: Connect: ppp0 <--> /dev/pts/1
Ιουλ 12 08:44:22 Desktop pppd[8923]: Connect: ppp0 <--> /dev/pts/1
Ιουλ 12 08:44:23 Desktop pptp[8942]: nm-pptp-service-8913 log[ctrlp_rep:pptp_ctrl.c:258]: Sent control packet type is 1 'Start-Control-Connection-Request'
Ιουλ 12 08:44:23 Desktop pptp[8942]: nm-pptp-service-8913 log[ctrlp_disp:pptp_ctrl.c:781]: Received Start Control Connection Reply
Ιουλ 12 08:44:23 Desktop pptp[8942]: nm-pptp-service-8913 log[ctrlp_disp:pptp_ctrl.c:815]: Client connection established.
Ιουλ 12 08:44:24 Desktop pptp[8942]: nm-pptp-service-8913 log[ctrlp_rep:pptp_ctrl.c:258]: Sent control packet type is 7 'Outgoing-Call-Request'
Ιουλ 12 08:44:24 Desktop pptp[8942]: nm-pptp-service-8913 log[ctrlp_disp:pptp_ctrl.c:900]: Received Outgoing Call Reply.
Ιουλ 12 08:44:24 Desktop pptp[8942]: nm-pptp-service-8913 log[ctrlp_disp:pptp_ctrl.c:938]: Outgoing call established (call ID 37580, peer's call ID 53533).
Ιουλ 12 08:44:53 Desktop pppd[8923]: LCP: timeout sending Config-Requests
Ιουλ 12 08:44:53 Desktop NetworkManager[8923]: LCP: timeout sending Config-Requests
Ιουλ 12 08:44:53 Desktop NetworkManager[8923]: Connection terminated.
Ιουλ 12 08:44:53 Desktop pppd[8923]: Connection terminated.
Ιουλ 12 08:44:53 Desktop NetworkManager[643]: <info> [] vpn-connection[*********,"*******",0]: VPN service dis>
Ιουλ 12 08:44:53 Desktop pptp[8928]: nm-pptp-service-8913 warn[decaps_hdlc:pptp_gre.c:226]: short read (-1): Input/output error
Ιουλ 12 08:44:53 Desktop pptp[8928]: nm-pptp-service-8913 warn[decaps_hdlc:pptp_gre.c:238]: pppd may have shutdown, see pppd log
Ιουλ 12 08:44:53 Desktop NetworkManager[8923]: Terminating on signal 15
Ιουλ 12 08:44:53 Desktop NetworkManager[8923]: Child process /usr/sbin/pptp **.**.**.** --nolaunchpppd --loglevel 0 --logstring nm-pptp-service-8913 (pid 8926) termina>
Ιουλ 12 08:44:53 Desktop NetworkManager[8923]: Modem hangup
When searching for the reason I saw many cases where the above was due to GRE protocol restrictions by the ISP. Is there any way to have a better insight in the reason why this happens. For example if it is due to GRE how can I confirm this? The ISP helpdesk is not willing to help unless I have some concrete requirement.
Edit: Also TCP dump returns the following when tracking GRE:
GREv1, call 42081, seq 1, length 36: LCP, Conf-Request (0x01), id 1, length 22
As the above request remains unanswered and although it is sent repeatedly, I guess that indeed the reason is GRE restriction.
