Не удается подключиться к PPTP VPN

Я установил PPTP VPN-сервер (небезопасный, я знаю, но это в основном опыт обучения) с использованием PPTPD на запасном рабочем столе Ubuntu 15.10, который у меня был, но я не могу подключиться к нему из Linux или Windows. Когда я пытаюсь подключиться с компьютера Antergos, я получаю следующий вывод от Network Manager:

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.

Раньше у меня это работало с той же конфигурацией на машине Antergos, но я не могу заставить ее работать под Ubuntu.

Мой маршрутизатор настроен на пересылку порта 1723 на рабочий стол Ubuntu, и из журнала подключений выше видно, что он проходит и начинает общаться с сервером, но затем разрывает соединение.

Ниже приведены правила iptables, присутствующие на сервере Ubuntu, на котором размещается VPN:

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

Любое понимание? Заранее спасибо!