Error 619

The environment is as follows:

            CentOS （pptpServer) public network IP win7 (PPTP client) intranet IP

            When using the client to connect to the server, report the network error 619.

            Use mobile phone WiFi hotspots, client connect hotspots, then use VPN, report error 619.

  Log on the CentOS server. The following are the same errors.

Aug 31 11:07:36  pptpd[9162]: CTRL: PTY read or GRE write failed (pty,gre)=(6,7)
Aug 31 11:07:36  pptpd[9162]: CTRL: Client 14.16.135.232 control connection finished
Aug 31 11:07:47  pptpd[9214]: CTRL: Client 14.16.135.232 control connection started
Aug 31 11:07:47  pptpd[9214]: CTRL: Starting call (launching pppd, opening GRE)
Aug 31 11:07:47  pppd[9215]: Plugin /usr/lib64/pptpd/pptpd-logwtmp.so loaded.
Aug 31 11:07:47  pppd[9215]: pppd 2.4.5 started by root, uid 0
Aug 31 11:07:47  pppd[9215]: Using interface ppp0
Aug 31 11:07:47  pppd[9215]: Connect: ppp0 <–> /dev/pts/1
Aug 31 11:07:47  NetworkManager[640]: <info>  (ppp0): new Generic device (carrier: UNKNOWN, driver: ‘unknown’, ifindex: 20)    Question 1
Aug 31 11:08:17  pppd[9215]: LCP: timeout sending Config-Requests     Question 2
Aug 31 11:08:17  pppd[9215]: Connection terminated.
Aug 31 11:08:17  pppd[9215]: Modem hangup
Aug 31 11:08:17  pppd[9215]: Exit.
Aug 31 11:08:17  pptpd[9214]: GRE: read(fd=6,buffer=7f234b1cb480,len=8196) from PTY failed: status = -1 error = Input/output error, usually caused by unexpected termination of pppd, check option syntax and pppd logs
Aug 31 11:08:17  pptpd[9214]: CTRL: PTY read or GRE write failed (pty,gre)=(6,7)
Aug 31 11:08:17  pptpd[9214]: CTRL: Client 14.16.135.232 control connection finished

The problem is still in the position. Record it.

The following questions are as follows:

1）For problem 1, turn off NetworkManager.

    sudo systemctl NetwokManager stop

2)For Question 2, change the configuration file / etc / PPP / options. pptpd, shield the unused, and add the allowed

   # BSD licensed ppp-2.4.2 upstream with MPPE only, kernel module ppp_mppe.o
# {{{
#refuse-pap
#refuse-chap
#refuse-mschap
# Require the peer to authenticate itself using MS-CHAPv2 [Microsoft
# Challenge Handshake Authentication Protocol, Version 2] authentication.
require-mschap-v2
# Require MPPE 128-bit encryption
# (note that MPPE requires the use of MSCHAP-V2 during authentication)
#require-mppe-128
require-chap #tAdd the allowed way
# }}}

After modification, the connection is still unsuccessful. The server terminal exception log is as follows:
Aug 31 13:41:40 testhostname0001 pptpd[15464]: CTRL: Client 14.16.135.232 control connection started
Aug 31 13:41:40 testhostname0001 pptpd[15464]: CTRL: Starting call (launching pppd, opening GRE)
Aug 31 13:41:40 testhostname0001 pppd[15465]: Plugin /usr/lib64/pptpd/pptpd-logwtmp.so loaded.
Aug 31 13:41:40 testhostname0001 pppd[15465]: pppd 2.4.5 started by root, uid 0
Aug 31 13:41:40 testhostname0001 pppd[15465]: Using interface ppp0
Aug 31 13:41:40 testhostname0001 pppd[15465]: Connect: ppp0 <–> /dev/pts/2
Aug 31 13:42:10 testhostname0001 pppd[15465]: LCP: timeout sending Config-Requests  Question 1
Aug 31 13:42:10 testhostname0001 pppd[15465]: Connection terminated.
Aug 31 13:42:10 testhostname0001 pppd[15465]: Modem hangup
Aug 31 13:42:10 testhostname0001 pppd[15465]: Exit.
Aug 31 13:42:10 testhostname0001 pptpd[15464]: GRE: read(fd=6,buffer=7f559256a480,len=8196) from PTY failed: status = -1 error = Input/output error, usually caused by unexpected termination of pppd, check option syntax and pppd logs
Aug 31 13:42:10 testhostname0001 pptpd[15464]: CTRL: PTY read or GRE write failed (pty,gre)=(6,7)
Aug 31 13:42:10 testhostname0001 pptpd[15464]: CTRL: Client 14.16.135.232 control connection finished

The problem is still not resolved.

 Baidu learned that:

Many people get stuck in the VPN to verify the username and password, and then 619 errors occur. More than 90% of these errors are caused by the fact that devices in the client-to-server network do not support GRE or NAT-T. The most common ones are due to unsupported routers on the client side.You can dial VPN immediately after the replacement. This error is also reflected in the server’s log. for example

The following is inconsistent with the encryption and decryption of the two sides:

There are other questions to check here.
http://pptpclient.sourceforge.net/howto-diagnosis.phtml

Because of this problem on both the client side and sever side, the client side (ubuntu) was changed according to the method on the network:

1）Add tonf_conntrack_pptp nf_conntrack_proto_gre Modular

    sudo modprobe nf_conntrack_pptp

2) Add NAT module

   sudo modprobe ip_nat_pptp

3)Open silent mode

   Modify /etc/ppp/options file

   # With this option, pppd will not transmit LCP packets to initiate a

  # connection until a valid LCP packet is received from the peer (as for

  # the "passive" option with old versions of pppd).

  silent

   Then the client side problem is solved, because the server side uses centos, did not find the relevant files, so the server side still has this problem.

 Note: Useful URL: https://askubuntu.com/questions/269399/failed-to-connect-to-pptp-vpn-server-on-ubuntu