我正在尝试使用 Ubuntu 21.04 笔记本电脑上的 network-manager-pptp 连接到我的大学 VPN。VPN 设置为根据所需设置使用 MSCHAPv2 和 MPPE。我曾经能够连接到 VPN（几天前），但之后就再也没有连接上了。
从那时起，当我尝试连接时，会出现一个连接错误弹出窗口，提示“激活网络连接失败”
从我的日志来看，关键行在我看来是：
May 23 08:11:02 ce3xxx pptp[11770]: nm-pptp-service-11746 log[ctrlp_disp:pptp_ctrl.c:938]: Outgoing call established (call ID 4665, peer's call ID 34688).
May 23 08:11:32 ce3xxx pppd[11750]: LCP: timeout sending Config-Requests
May 23 08:11:32 ce3xxx NetworkManager[11750]: LCP: timeout sending Config-Requests
May 23 08:11:32 ce3xxx NetworkManager[11750]: Connection terminated.
日志的更扩展部分（使用获得sudo journalctl -b 0 -u NetworkManager | tail -n 60）包括：
May 25 09:14:51 ce3xxx NetworkManager[745]: <info> [1621930491.1891] audit: op="connection-activate" uuid="4387ae53-1b36-4522-8ff4-01ebdc6ebf8d" name="College VPN" pid=1632 uid=1000 result="success"
May 25 09:14:51 ce3xxx NetworkManager[745]: <info> [1621930491.1941] vpn-connection[0x55626e4da6d0,4387ae53-1b36-4522-8ff4-01ebdc6ebf8d,"College VPN",0]: Started the VPN service, PID 19517
May 25 09:14:51 ce3xxx NetworkManager[745]: <info> [1621930491.1995] vpn-connection[0x55626e4da6d0,4387ae53-1b36-4522-8ff4-01ebdc6ebf8d,"College VPN",0]: Saw the service appear; activating connection
May 25 09:14:51 ce3xxx NetworkManager[745]: <info> [1621930491.2036] vpn-connection[0x55626e4da6d0,4387ae53-1b36-4522-8ff4-01ebdc6ebf8d,"College VPN",0]: VPN connection: (ConnectInteractive) reply received
May 25 09:14:51 ce3xxx NetworkManager[745]: <info> [1621930491.3193] vpn-connection[0x55626e4da6d0,4387ae53-1b36-4522-8ff4-01ebdc6ebf8d,"College VPN",0]: VPN plugin: state changed: starting (3)
May 25 09:14:51 ce3xxx pppd[19521]: Plugin /usr/lib/pppd/2.4.7/nm-pptp-pppd-plugin.so loaded.
May 25 09:14:51 ce3xxx NetworkManager[19521]: Plugin /usr/lib/pppd/2.4.7/nm-pptp-pppd-plugin.so loaded.
May 25 09:14:51 ce3xxx pppd[19521]: pppd 2.4.7 started by root, uid 0
May 25 09:14:51 ce3xxx pppd[19521]: Using interface ppp0
May 25 09:14:51 ce3xxx NetworkManager[19521]: Using interface ppp0
May 25 09:14:51 ce3xxx NetworkManager[19521]: Connect: ppp0 <--> /dev/pts/1
May 25 09:14:51 ce3xxx pppd[19521]: Connect: ppp0 <--> /dev/pts/1
May 25 09:14:51 ce3xxx NetworkManager[745]: <info> [1621930491.3259] manager: (ppp0): new Ppp device (/org/freedesktop/NetworkManager/Devices/18)
May 25 09:14:51 ce3xxx pptp[19528]: nm-pptp-service-19517 log[main:pptp.c:353]: The synchronous pptp option is NOT activated
May 25 09:14:51 ce3xxx pptp[19542]: nm-pptp-service-19517 log[ctrlp_rep:pptp_ctrl.c:258]: Sent control packet type is 1 'Start-Control-Connection-Request'
May 25 09:14:51 ce3xxx pptp[19542]: nm-pptp-service-19517 log[ctrlp_disp:pptp_ctrl.c:781]: Received Start Control Connection Reply
May 25 09:14:51 ce3xxx pptp[19542]: nm-pptp-service-19517 log[ctrlp_disp:pptp_ctrl.c:815]: Client connection established.
May 25 09:14:52 ce3xxx pptp[19542]: nm-pptp-service-19517 log[ctrlp_rep:pptp_ctrl.c:258]: Sent control packet type is 7 'Outgoing-Call-Request'
May 25 09:14:52 ce3xxx pptp[19542]: nm-pptp-service-19517 log[ctrlp_disp:pptp_ctrl.c:900]: Received Outgoing Call Reply.
May 25 09:14:52 ce3xxx pptp[19542]: nm-pptp-service-19517 log[ctrlp_disp:pptp_ctrl.c:938]: Outgoing call established (call ID 48238, peer's call ID 23296).
May 25 09:15:22 ce3xxx pppd[19521]: LCP: timeout sending Config-Requests
May 25 09:15:22 ce3xxx NetworkManager[19521]: LCP: timeout sending Config-Requests
May 25 09:15:22 ce3xxx NetworkManager[19521]: Connection terminated.
May 25 09:15:22 ce3xxx pppd[19521]: Connection terminated.
May 25 09:15:22 ce3xxx NetworkManager[745]: <warn> [1621930522.3536] vpn-connection[0x55626e4da6d0,4387ae53-1b36-4522-8ff4-01ebdc6ebf8d,"College VPN",0]: VPN plugin: failed: connect-failed (1)
May 25 09:15:22 ce3xxx NetworkManager[745]: <info> [1621930522.3536] vpn-connection[0x55626e4da6d0,4387ae53-1b36-4522-8ff4-01ebdc6ebf8d,"College VPN",0]: VPN plugin: state changed: stopping (5)
May 25 09:15:22 ce3xxx NetworkManager[745]: <info> [1621930522.3536] vpn-connection[0x55626e4da6d0,4387ae53-1b36-4522-8ff4-01ebdc6ebf8d,"College VPN",0]: VPN plugin: state changed: stopped (6)
May 25 09:15:22 ce3xxx NetworkManager[745]: <info> [1621930522.3595] vpn-connection[0x55626e4da6d0,4387ae53-1b36-4522-8ff4-01ebdc6ebf8d,"College VPN",0]: VPN service disappeared
May 25 09:15:22 ce3xxx pptp[19528]: nm-pptp-service-19517 warn[decaps_hdlc:pptp_gre.c:226]: short read (-1): Input/output error
May 25 09:15:22 ce3xxx NetworkManager[19521]: Terminating on signal 15
May 25 09:15:22 ce3xxx NetworkManager[19521]: Child process /sbin/pptp 146.179.1.147 --nolaunchpppd --loglevel 0 --logstring nm-pptp-service-19517 (pid 19524) terminated with signal 15
May 25 09:15:22 ce3xxx NetworkManager[19521]: Modem hangup
May 25 09:15:22 ce3xxx pptp[19528]: nm-pptp-service-19517 warn[decaps_hdlc:pptp_gre.c:238]: pppd may have shutdown, see pppd log
May 25 09:15:22 ce3xxx pppd[19521]: Terminating on signal 15
May 25 09:15:22 ce3xxx pppd[19521]: Child process /sbin/pptp 146.179.1.147 --nolaunchpppd --loglevel 0 --logstring nm-pptp-service-19517 (pid 19524) terminated with signal 15
May 25 09:15:22 ce3xxx pppd[19521]: Modem hangup
May 25 09:15:22 ce3xxx pppd[19521]: Exit.
非常感谢任何建议
答案1
从来没有找到确切的解决方案，但通过切换到 OpenVPN，我能够毫无问题地连接到同一个 VPN。