我有一台安装了 ubuntu 14.04 LTS 的 Dell Precision M6300 笔记本电脑，我在工作中使用它来运行 Linux 软件。我在卫星办公室工作，并使用 VPN 连接到总部以获取软件许可证，并且运行正常。
但是，我确实注意到，每当我在家工作时（无论是通过以太网还是无线网络），这台笔记本电脑都会显示“VPN 连接失败”消息。我确实找到了一种解决方法，即断开笔记本电脑与家用路由器的连接，打开手机上的移动热点，将笔记本电脑连接到移动热点，然后通过移动互联网连接建立 VPN 连接，这样就可以正常工作了。
因此，这台 ubuntu 笔记本电脑成功地从卫星办公室、通过我的移动互联网和其他几个位置（其他人的家）建立了 VPN 连接，但无法连接到我的家庭网络（无论是有线还是无线）。我还应该提到，我还有一台 Windows 7 工作笔记本电脑，即使在我家，使用相同的 VPN 连接也没有问题。
我在英国，我家里的 ISP 是 Virgin Media，路由器是“Super Hub VMDG490”。
我该怎么做才能诊断或修复该问题？
当我使用tail -f /var/log/syslog并尝试从我的家庭网络连接（但失败了）时，我得到了以下信息：
Feb 22 17:27:46 VEC-ubuntu-precision-m6300 NetworkManager[764]: <warn> error disconnecting VPN: Could not process the request because no VPN connection was active.
Feb 22 17:27:52 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> VPN service 'pptp' disappeared
Feb 22 17:28:18 VEC-ubuntu-precision-m6300 pptp[2399]: nm-pptp-service-2387 warn[open_inetsock:pptp_callmgr.c:329]: connect: Connection timed out
Feb 22 17:28:18 VEC-ubuntu-precision-m6300 pptp[2399]: nm-pptp-service-2387 fatal[callmgr_main:pptp_callmgr.c:127]: Could not open control connection to XX.XX.XX.XXX
Feb 22 17:28:18 VEC-ubuntu-precision-m6300 pptp[2396]: nm-pptp-service-2387 fatal[open_callmgr:pptp.c:487]: Call manager exited with error 256
Feb 22 17:29:05 VEC-ubuntu-precision-m6300 wpa_supplicant[802]: wlan0: CTRL-EVENT-SCAN-STARTED
Feb 22 17:29:10 VEC-ubuntu-precision-m6300 wpa_supplicant[802]: nl80211: send_and_recv->nl_recvmsgs failed: -33
Feb 22 17:29:18 VEC-ubuntu-precision-m6300 pptp[2431]: nm-pptp-service-2422 warn[open_inetsock:pptp_callmgr.c:329]: connect: Connection timed out
Feb 22 17:29:18 VEC-ubuntu-precision-m6300 pptp[2431]: nm-pptp-service-2422 fatal[callmgr_main:pptp_callmgr.c:127]: Could not open control connection to XX.XX.XX.XXX
Feb 22 17:29:18 VEC-ubuntu-precision-m6300 pptp[2429]: nm-pptp-service-2422 fatal[open_callmgr:pptp.c:487]: Call manager exited with error 256
Feb 22 17:30:07 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> Starting VPN service 'pptp'...
Feb 22 17:30:07 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> VPN service 'pptp' started (org.freedesktop.NetworkManager.pptp), PID 2463
Feb 22 17:30:07 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> VPN service 'pptp' appeared; activating connections
Feb 22 17:30:07 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> VPN plugin state changed: starting (3)
Feb 22 17:30:07 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> VPN connection 'Vectayn' (Connect) reply received.
Feb 22 17:30:07 VEC-ubuntu-precision-m6300 pppd[2467]: Plugin /usr/lib/pppd/2.4.5/nm-pptp-pppd-plugin.so loaded.
Feb 22 17:30:07 VEC-ubuntu-precision-m6300 pppd[2467]: pppd 2.4.5 started by root, uid 0
Feb 22 17:30:07 VEC-ubuntu-precision-m6300 pppd[2467]: Using interface ppp0
Feb 22 17:30:07 VEC-ubuntu-precision-m6300 pppd[2467]: Connect: ppp0 <--> /dev/pts/3
Feb 22 17:30:07 VEC-ubuntu-precision-m6300 NetworkManager[764]: SCPlugin-Ifupdown: devices added (path: /sys/devices/virtual/net/ppp0, iface: ppp0)
Feb 22 17:30:07 VEC-ubuntu-precision-m6300 NetworkManager[764]: SCPlugin-Ifupdown: device added (path: /sys/devices/virtual/net/ppp0, iface: ppp0): no ifupdown configuration found.
Feb 22 17:30:07 VEC-ubuntu-precision-m6300 NetworkManager[764]: <warn> /sys/devices/virtual/net/ppp0: couldn't determine device driver; ignoring...
Feb 22 17:30:07 VEC-ubuntu-precision-m6300 pptp[2470]: nm-pptp-service-2463 log[main:pptp.c:314]: The synchronous pptp option is NOT activated
Feb 22 17:30:38 VEC-ubuntu-precision-m6300 pppd[2467]: LCP: timeout sending Config-Requests
Feb 22 17:30:38 VEC-ubuntu-precision-m6300 pppd[2467]: Connection terminated.
Feb 22 17:30:38 VEC-ubuntu-precision-m6300 NetworkManager[764]: <warn> VPN plugin failed: 1
Feb 22 17:30:38 VEC-ubuntu-precision-m6300 NetworkManager[764]: SCPlugin-Ifupdown: devices removed (path: /sys/devices/virtual/net/ppp0, iface: ppp0)
Feb 22 17:30:38 VEC-ubuntu-precision-m6300 pppd[2467]: Modem hangup
Feb 22 17:30:38 VEC-ubuntu-precision-m6300 NetworkManager[764]: <warn> VPN plugin failed: 1
Feb 22 17:30:43 VEC-ubuntu-precision-m6300 pppd[2467]: Exit.
Feb 22 17:30:43 VEC-ubuntu-precision-m6300 NetworkManager[764]: <warn> VPN plugin failed: 1
Feb 22 17:30:43 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> VPN plugin state changed: stopped (6)
Feb 22 17:30:43 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> VPN plugin state change reason: 0
Feb 22 17:30:43 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> Policy set 'VM247013-2G' (wlan0) as default for IPv4 routing and DNS.
Feb 22 17:30:43 VEC-ubuntu-precision-m6300 NetworkManager[764]: <warn> error disconnecting VPN: Could not process the request because no VPN connection was active.
Feb 22 17:30:48 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> VPN service 'pptp' disappeared
当我通过移动网络执行相同操作（并且有效）时，我得到了以下信息：
Feb 22 17:46:40 VEC-ubuntu-precision-m6300 dnsmasq[1100]: setting upstream servers from DBus
Feb 22 17:46:40 VEC-ubuntu-precision-m6300 dnsmasq[1100]: using nameserver 192.168.43.1#53
Feb 22 17:46:40 VEC-ubuntu-precision-m6300 avahi-daemon[676]: Joining mDNS multicast group on interface wlan0.IPv6 with address aa80::21a:3aaa:aa12:aa99.
Feb 22 17:46:40 VEC-ubuntu-precision-m6300 avahi-daemon[676]: New relevant interface wlan0.IPv6 for mDNS.
Feb 22 17:46:40 VEC-ubuntu-precision-m6300 avahi-daemon[676]: Registering new address record for aa80::21a:3aaa:aa12:aa99 on wlan0.*.
Feb 22 17:46:40 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> Activation (wlan0) successful, device activated.
Feb 22 17:46:40 VEC-ubuntu-precision-m6300 dbus[628]: [system] Activating service name='org.freedesktop.nm_dispatcher' (using servicehelper)
Feb 22 17:46:40 VEC-ubuntu-precision-m6300 dbus[628]: [system] Successfully activated service 'org.freedesktop.nm_dispatcher'
Feb 22 17:46:40 VEC-ubuntu-precision-m6300 whoopsie[1015]: online
Feb 22 17:46:47 VEC-ubuntu-precision-m6300 ntpdate[2687]: adjust time server TT.TTT.TT.TTT offset 0.090452 sec
Feb 22 17:46:58 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> (wlan0): IP6 addrconf timed out or failed.
Feb 22 17:46:58 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> Activation (wlan0) Stage 4 of 5 (IPv6 Configure Timeout) scheduled...
Feb 22 17:46:58 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> Activation (wlan0) Stage 4 of 5 (IPv6 Configure Timeout) started...
Feb 22 17:46:58 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> Activation (wlan0) Stage 4 of 5 (IPv6 Configure Timeout) complete.
Feb 22 17:47:08 VEC-ubuntu-precision-m6300 wpa_supplicant[802]: wlan0: CTRL-EVENT-SCAN-STARTED
Feb 22 17:47:12 VEC-ubuntu-precision-m6300 wpa_supplicant[802]: nl80211: send_and_recv->nl_recvmsgs failed: -33
Feb 22 17:47:20 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> Starting VPN service 'pptp'...
Feb 22 17:47:20 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> VPN service 'pptp' started (org.freedesktop.NetworkManager.pptp), PID 2710
Feb 22 17:47:20 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> VPN service 'pptp' appeared; activating connections
Feb 22 17:47:20 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> VPN plugin state changed: init (1)
Feb 22 17:47:20 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> VPN plugin state changed: starting (3)
Feb 22 17:47:20 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> VPN connection 'Vectayn' (Connect) reply received.
Feb 22 17:47:20 VEC-ubuntu-precision-m6300 pppd[2714]: Plugin /usr/lib/pppd/2.4.5/nm-pptp-pppd-plugin.so loaded.
Feb 22 17:47:20 VEC-ubuntu-precision-m6300 pppd[2714]: pppd 2.4.5 started by root, uid 0
Feb 22 17:47:20 VEC-ubuntu-precision-m6300 pppd[2714]: Using interface ppp0
Feb 22 17:47:20 VEC-ubuntu-precision-m6300 pppd[2714]: Connect: ppp0 <--> /dev/pts/3
Feb 22 17:47:20 VEC-ubuntu-precision-m6300 pptp[2717]: nm-pptp-service-2710 log[main:pptp.c:314]: The synchronous pptp option is NOT activated
Feb 22 17:47:20 VEC-ubuntu-precision-m6300 NetworkManager[764]: SCPlugin-Ifupdown: devices added (path: /sys/devices/virtual/net/ppp0, iface: ppp0)
Feb 22 17:47:20 VEC-ubuntu-precision-m6300 NetworkManager[764]: SCPlugin-Ifupdown: device added (path: /sys/devices/virtual/net/ppp0, iface: ppp0): no ifupdown configuration found.
Feb 22 17:47:20 VEC-ubuntu-precision-m6300 NetworkManager[764]: <warn> /sys/devices/virtual/net/ppp0: couldn't determine device driver; ignoring...
Feb 22 17:47:20 VEC-ubuntu-precision-m6300 pptp[2734]: nm-pptp-service-2710 log[ctrlp_rep:pptp_ctrl.c:251]: Sent control packet type is 1 'Start-Control-Connection-Request'
Feb 22 17:47:20 VEC-ubuntu-precision-m6300 pptp[2734]: nm-pptp-service-2710 log[ctrlp_disp:pptp_ctrl.c:739]: Received Start Control Connection Reply
Feb 22 17:47:20 VEC-ubuntu-precision-m6300 pptp[2734]: nm-pptp-service-2710 log[ctrlp_disp:pptp_ctrl.c:773]: Client connection established.
Feb 22 17:47:21 VEC-ubuntu-precision-m6300 pptp[2734]: nm-pptp-service-2710 log[ctrlp_rep:pptp_ctrl.c:251]: Sent control packet type is 7 'Outgoing-Call-Request'
Feb 22 17:47:21 VEC-ubuntu-precision-m6300 pptp[2734]: nm-pptp-service-2710 log[ctrlp_disp:pptp_ctrl.c:858]: Received Outgoing Call Reply.
Feb 22 17:47:21 VEC-ubuntu-precision-m6300 pptp[2734]: nm-pptp-service-2710 log[ctrlp_disp:pptp_ctrl.c:897]: Outgoing call established (call ID 0, peer's call ID 10015).
Feb 22 17:47:21 VEC-ubuntu-precision-m6300 pppd[2714]: CHAP authentication succeeded
Feb 22 17:47:21 VEC-ubuntu-precision-m6300 kernel: [ 1556.382975] PPP BSD Compression module registered
Feb 22 17:47:21 VEC-ubuntu-precision-m6300 kernel: [ 1556.397676] PPP Deflate Compression module registered
Feb 22 17:47:22 VEC-ubuntu-precision-m6300 pppd[2714]: local IP address L.LL.LLL.LLL
Feb 22 17:47:22 VEC-ubuntu-precision-m6300 pppd[2714]: remote IP address R.RR.RRR.RR
Feb 22 17:47:22 VEC-ubuntu-precision-m6300 pppd[2714]: primary DNS address D.DD.DDD.DDD
Feb 22 17:47:22 VEC-ubuntu-precision-m6300 pppd[2714]: secondary DNS address 8.8.8.8
Feb 22 17:47:22 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> VPN connection 'Vectayn' (IP4 Config Get) reply received from old-style plugin.
Feb 22 17:47:22 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> VPN Gateway: GG.GG.GG.GGG
Feb 22 17:47:22 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> Tunnel Device: ppp0
Feb 22 17:47:22 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> IPv4 configuration:
Feb 22 17:47:22 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> Internal Address: L.LL.LLL.LLL
Feb 22 17:47:22 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> Internal Prefix: 32
Feb 22 17:47:22 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> Internal Point-to-Point Address: R.RR.RRR.RR
Feb 22 17:47:22 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> Maximum Segment Size (MSS): 0
Feb 22 17:47:22 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> Forbid Default Route: no
Feb 22 17:47:22 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> Internal DNS: D.DD.DDD.DDD
Feb 22 17:47:22 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> Internal DNS: 8.8.8.8
Feb 22 17:47:22 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> DNS Domain: '(none)'
Feb 22 17:47:22 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> No IPv6 configuration
Feb 22 17:47:23 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> VPN connection 'Vectayn' (IP Config Get) complete.
Feb 22 17:47:23 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> Policy set 'Vectayn' (ppp0) as default for IPv4 routing and DNS.
Feb 22 17:47:23 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> Writing DNS information to /sbin/resolvconf
Feb 22 17:47:23 VEC-ubuntu-precision-m6300 dnsmasq[1100]: setting upstream servers from DBus
Feb 22 17:47:23 VEC-ubuntu-precision-m6300 dnsmasq[1100]: using nameserver 8.8.8.8#53
Feb 22 17:47:23 VEC-ubuntu-precision-m6300 dnsmasq[1100]: using nameserver D.DD.DDD.DDD#53
Feb 22 17:47:23 VEC-ubuntu-precision-m6300 NetworkManager[764]: <info> VPN plugin state changed: started (4)
Feb 22 17:47:23 VEC-ubuntu-precision-m6300 dbus[628]: [system] Activating service name='org.freedesktop.nm_dispatcher' (using servicehelper)
Feb 22 17:47:23 VEC-ubuntu-precision-m6300 dbus[628]: [system] Successfully activated service 'org.freedesktop.nm_dispatcher'
Feb 22 17:47:23 VEC-ubuntu-precision-m6300 pptp[2734]: nm-pptp-service-2710 log[logecho:pptp_ctrl.c:677]: Echo Request received.
Feb 22 17:47:23 VEC-ubuntu-precision-m6300 pptp[2734]: nm-pptp-service-2710 log[ctrlp_rep:pptp_ctrl.c:251]: Sent control packet type is 6 'Echo-Reply'
Feb 22 17:47:31 VEC-ubuntu-precision-m6300 ntpdate[2789]: adjust time server TT.TTT.TT.TTT offset 0.069434 sec
答案1
我以为这是 ubuntu 的问题，因为 Windows 可以正常工作。但是，我通过更改路由器设置解决了这个问题。谷歌搜索“VMDG490 VPN”得到了很多有用的链接，例如这里，这里和这里。
Virgin Media 集线器默认禁用“PPTP 直通”。因此，我需要登录路由器192.168.0.1，方法是在浏览器中输入设置密码，转到“高级设置”，然后转到“安全/防火墙”，然后在防火墙页面上勾选“PPTP 直通”（其他 VPN 用户可能需要勾选“IPSec 直通”），最后单击“应用”。
这一变化解决了这个问题：我的 ubuntu 笔记本电脑现在使用我的家庭网络连接到 VPN。
抱歉，这已经偏离主题了，但直到我找到解决方案后才意识到这与 ubuntu 无关。然而，为什么 Windows 在使用同一路由器连接到同一 VPN 服务器时能够正常工作仍然是个谜，上面链接的指南是针对 Windows 用户的，因此 Windows 不应该能够正常工作。