我在闲置的 Ubuntu 15.10 桌面上使用 PPTPD 设置了一个 PPTP VPN 服务器（我知道这不安全，但这项工作主要是为了学习），但无法从 Linux 或 Windows 连接到它。当我尝试从 Antergos 机器连接时，我从网络管理器获得以下输出：
Mar 15 10:21:14 mblasco-XPS NetworkManager[377]: <info> Starting VPN service 'pptp'...
Mar 15 10:21:14 mblasco-XPS NetworkManager[377]: <info> VPN service 'pptp' started (org.freedesktop.NetworkManager.pptp), PID 2903
Mar 15 10:21:14 mblasco-XPS NetworkManager[377]: <info> VPN service 'pptp' appeared; activating connections
Mar 15 10:21:14 mblasco-XPS NetworkManager[377]: <info> VPN plugin state changed: init (1)
Mar 15 10:21:15 mblasco-XPS NetworkManager[377]: <info> VPN connection 'HawkHouse' (ConnectInteractive) reply received.
Mar 15 10:21:15 mblasco-XPS NetworkManager[377]: <info> VPN plugin state changed: starting (3)
Mar 15 10:21:15 mblasco-XPS NetworkManager[377]: ** Message: pppd started with pid 2910
Mar 15 10:21:15 mblasco-XPS NetworkManager[377]: <info> VPN connection 'HawkHouse' (Connect) reply received.
Mar 15 10:21:15 mblasco-XPS pppd[2910]: Plugin /usr/lib/pppd/2.4.7/nm-pptp-pppd-plugin.so loaded.
Mar 15 10:21:15 mblasco-XPS NetworkManager[377]: Plugin /usr/lib/pppd/2.4.7/nm-pptp-pppd-plugin.so loaded.
Mar 15 10:21:15 mblasco-XPS NetworkManager[377]: ** Message: nm-pptp-ppp-plugin: (plugin_init): initializing
Mar 15 10:21:15 mblasco-XPS pppd[2910]: pppd 2.4.7 started by root, uid 0
Mar 15 10:21:15 mblasco-XPS NetworkManager[377]: ** Message: nm-pptp-ppp-plugin: (nm_phasechange): status 3 / phase 'serial connection'
Mar 15 10:21:15 mblasco-XPS NetworkManager[377]: <info> (ppp0): new Generic device (carrier: UNKNOWN, driver: 'unknown', ifindex: 16)
Mar 15 10:21:15 mblasco-XPS pppd[2910]: Using interface ppp0
Mar 15 10:21:15 mblasco-XPS NetworkManager[377]: Using interface ppp0
Mar 15 10:21:15 mblasco-XPS pppd[2910]: Connect: ppp0 <--> /dev/pts/1
Mar 15 10:21:15 mblasco-XPS NetworkManager[377]: Connect: ppp0 <--> /dev/pts/1
Mar 15 10:21:15 mblasco-XPS NetworkManager[377]: ** Message: nm-pptp-ppp-plugin: (nm_phasechange): status 5 / phase 'establish'
Mar 15 10:21:15 mblasco-XPS pptp[2912]: nm-pptp-service-2903 log[main:pptp.c:333]: The synchronous pptp option is NOT activated
Mar 15 10:21:15 mblasco-XPS pptp[2922]: nm-pptp-service-2903 log[ctrlp_rep:pptp_ctrl.c:258]: Sent control packet type is 1 'Start-Control-Connection-Request'
Mar 15 10:21:15 mblasco-XPS pptp[2922]: nm-pptp-service-2903 log[ctrlp_disp:pptp_ctrl.c:758]: Received Start Control Connection Reply
Mar 15 10:21:15 mblasco-XPS pptp[2922]: nm-pptp-service-2903 log[ctrlp_disp:pptp_ctrl.c:792]: Client connection established.
Mar 15 10:21:16 mblasco-XPS pptp[2922]: nm-pptp-service-2903 log[ctrlp_rep:pptp_ctrl.c:258]: Sent control packet type is 7 'Outgoing-Call-Request'
Mar 15 10:21:16 mblasco-XPS pptp[2922]: nm-pptp-service-2903 log[ctrlp_disp:pptp_ctrl.c:877]: Received Outgoing Call Reply.
Mar 15 10:21:16 mblasco-XPS pptp[2922]: nm-pptp-service-2903 log[ctrlp_disp:pptp_ctrl.c:916]: Outgoing call established (call ID 0, peer's call ID 11).
Mar 15 10:21:16 mblasco-XPS pppd[2910]: Modem hangup
Mar 15 10:21:16 mblasco-XPS NetworkManager[377]: Modem hangup
Mar 15 10:21:16 mblasco-XPS NetworkManager[377]: ** Message: nm-pptp-ppp-plugin: (nm_phasechange): status 11 / phase 'disconnect'
Mar 15 10:21:16 mblasco-XPS NetworkManager[377]: Connection terminated.
Mar 15 10:21:16 mblasco-XPS pppd[2910]: Connection terminated.
Mar 15 10:21:16 mblasco-XPS NetworkManager[377]: <warn> (ppp0): failed to disable userspace IPv6LL address handling
Mar 15 10:21:16 mblasco-XPS NetworkManager[377]: <warn> VPN plugin failed: connect-failed (1)
Mar 15 10:21:16 mblasco-XPS NetworkManager[377]: ** Message: nm-pptp-ppp-plugin: (nm_phasechange): status 1 / phase 'dead'
Mar 15 10:21:16 mblasco-XPS NetworkManager[377]: ** Message: nm-pptp-ppp-plugin: (nm_exit_notify): cleaning up
Mar 15 10:21:16 mblasco-XPS NetworkManager[377]: ** (nm-pptp-service:2903): WARNING **: pppd exited with error code 16
Mar 15 10:21:16 mblasco-XPS NetworkManager[377]: <warn> VPN plugin failed: connect-failed (1)
Mar 15 10:21:16 mblasco-XPS NetworkManager[377]: <warn> VPN plugin failed: connect-failed (1)
Mar 15 10:21:16 mblasco-XPS NetworkManager[377]: <info> VPN plugin state changed: stopped (6)
Mar 15 10:21:16 mblasco-XPS NetworkManager[377]: <info> VPN plugin state change reason: unknown (0)
Mar 15 10:21:16 mblasco-XPS NetworkManager[377]: <warn> error disconnecting VPN: Could not process the request because no VPN connection was active.
我之前在 Antergos 机器上使用相同的配置运行过它，但似乎无法在 Ubuntu 下让它运行。
我已将路由器配置为将端口 1723 转发到 Ubuntu 桌面，并且从上面的连接日志中可以看出，它确实成功通过并开始与服务器通信，但随后断开了连接。
以下是托管 VPN 的 Ubuntu 服务器上的 iptables 规则：
Chain INPUT (policy ACCEPT)
target prot opt source destination
ACCEPT gre -- anywhere anywhere
ACCEPT tcp -- anywhere anywhere tcp dpt:1723 state NEW
Chain FORWARD (policy ACCEPT)
target prot opt source destination
TCPMSS tcp -- 192.168.1.0/24 anywhere tcp flags:SYN,RST/SYN TCPMSS clamp to PMTU
ACCEPT gre -- anywhere anywhere
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
有什么见解吗？提前致谢！
答案1
该问题已通过 ServerFault 上的 ALex_hha 建议的更改得到解决：https://serverfault.com/questions/763855/cannot-connect-to-pptp-vpn
答案2
在使用 VPN 时禁用防火墙（ufw 或 gufw）就可以了，我遇到了同样的问题。