Strange PPTP Server problem (AC66U)

[Marsi4eg]

I have a problem with PPTP vpn server. Here is a log:

Mar 12 17:19:49 pptpd[664]: CTRL: Client 10.10.1.100 control connection started
Mar 12 17:19:49 pptpd[664]: CTRL: Starting call (launching pppd, opening GRE)
Mar 12 17:19:49 pptp[665]: Plugin pptp.so loaded.
Mar 12 17:19:49 pptp[665]: PPTP plugin version 0.8.5 compiled for pppd-2.4.5, linux-2.6.22.19
Mar 12 17:19:49 pptp[665]: pppd 2.4.5 started by admin, uid 0
Mar 12 17:19:49 pptp[665]: Using interface ppp10
Mar 12 17:19:49 pptp[665]: Connect: ppp10 <--> pptp (10.10.1.100)
Mar 12 17:20:19 pptp[665]: LCP: timeout sending Config-Requests
Mar 12 17:20:19 pptp[665]: Connection terminated.
Mar 12 17:20:19 kernel: Interface ppp10 doesn't exist
Mar 12 17:20:19 pptp[665]: Modem hangup
Mar 12 17:20:19 pptp[665]: Exit.
Mar 12 17:20:19 pptpd[664]: CTRL: Client pppd TERM sending
Mar 12 17:20:19 pptpd[664]: CTRL: Client pppd finish wait
Mar 12 17:20:19 pptpd[664]: CTRL: Client 10.10.1.100 control connection finished
Mar 12 17:25:23 rc_service: httpd 320:notify_rc stop_pptpd

Sometimes the server just 'decides' to accept connections:

Mar 12 17:41:59 pptpd[672]: CTRL: Client 10.10.1.100 control connection started
Mar 12 17:41:59 pptpd[672]: CTRL: Starting call (launching pppd, opening GRE)
Mar 12 17:41:59 pptp[673]: Plugin pptp.so loaded.
Mar 12 17:41:59 pptp[673]: PPTP plugin version 0.8.5 compiled for pppd-2.4.5, linux-2.6.22.19
Mar 12 17:41:59 pptp[673]: pppd 2.4.5 started by admin, uid 0
Mar 12 17:41:59 pptp[673]: Using interface ppp10
Mar 12 17:41:59 pptp[673]: Connect: ppp10 <--> pptp (10.10.1.100)
Mar 12 17:42:02 pptpd[672]: CTRL: Ignored a SET LINK INFO packet with real ACCMs!
Mar 12 17:42:02 pptp[673]: MPPE 128-bit stateless compression enabled
Mar 12 17:42:03 pptp[673]: Cannot determine ethernet address for proxy ARP
Mar 12 17:42:03 pptp[673]: local  IP address 10.7.7.33
Mar 12 17:42:03 pptp[673]: remote IP address 192.168.10.2

This is really annoying. The server accepts my connection everytime I test it from inside router's subnet but LCP timeout appear when I try to connect from other networks.

It works on router start up but 'dies' after a few hours of idle. Rebooting the router does not help, flashing the router to the same firmware also helps.

I have also googled for this kind of problems and found the information that there may be some troubles with sending GRE packets between client and server.

The problem is not caused by iptables rules, I tested this with disabled firewall.

 

[Marsi4eg]

The same problem was detected also on N16 with 374.40
Tried to connect from two PCs with win7/win8 via wifi network and via cable and Android phone

Also disabled windows firewall, re-enabled it and created allow rule for GRE protocol - no success yet

and here is the same log from N16 which is running from another ISP

Mar 16 15:01:40 pptpd[7438]: CTRL: Client 193.108.38.6 control connection finished
Mar 16 15:11:01 pptpd[7478]: CTRL: Client 193.108.38.6 control connection started
Mar 16 15:11:01 pptpd[7478]: CTRL: Starting call (launching pppd, opening GRE)
Mar 16 15:11:01 pptp[7479]: Plugin pptp.so loaded.
Mar 16 15:11:01 pptp[7479]: PPTP plugin version 0.8.5 compiled for pppd-2.4.5, linux-2.6.22.19
Mar 16 15:11:01 pptp[7479]: pppd 2.4.5 started by admin, uid 0
Mar 16 15:11:01 pptp[7479]: Using interface ppp10
Mar 16 15:11:01 pptp[7479]: Connect: ppp10 <--> pptp (193.108.38.6)
Mar 16 15:11:31 pptp[7479]: LCP: timeout sending Config-Requests
Mar 16 15:11:31 pptp[7479]: Connection terminated.
Mar 16 15:11:31 kernel: Interface ppp10 doesn't exist
Mar 16 15:11:31 pptp[7479]: Modem hangup
Mar 16 15:11:31 pptp[7479]: Exit.

windows shows error 619 in this case

Maybe there's a way to make server accept connections again:
-stop pptp server in webui
-reboot
-start pptp server in webui

just restarting pptp server or just rebooting the router doesn't help