つまり、問題は基本的に、Ubuntu 14.04 でオフィスの VPN に接続しようとすると失敗するということです。
特別な設定はありませんが、PPTP であることは言及する価値があります。
サーバーに ping するのは簡単です。診断しやすくするためにどのような情報をここに載せればよいかわかりませんが、お知らせください。
出力は次のようになります。
Sep 29 17:24:27 pedri-home NetworkManager[912]: <info> Starting VPN service 'pptp'...
Sep 29 17:24:27 pedri-home NetworkManager[912]: <info> VPN service 'pptp' started (org.freedesktop.NetworkManager.pptp), PID 18760
Sep 29 17:24:27 pedri-home NetworkManager[912]: <info> VPN service 'pptp' appeared; activating connections
Sep 29 17:24:27 pedri-home NetworkManager[912]: <info> VPN plugin state changed: init (1)
Sep 29 17:24:27 pedri-home NetworkManager[912]: <info> VPN plugin state changed: starting (3)
Sep 29 17:24:27 pedri-home pppd[18764]: Plugin /usr/lib/pppd/2.4.5/nm-pptp-pppd-plugin.so loaded.
Sep 29 17:24:27 pedri-home NetworkManager[912]: <info> VPN connection 'Test2' (Connect) reply received.
Sep 29 17:24:27 pedri-home pppd[18764]: pppd 2.4.5 started by root, uid 0
Sep 29 17:24:27 pedri-home pppd[18764]: Using interface ppp0
Sep 29 17:24:27 pedri-home pppd[18764]: Connect: ppp0 <--> /dev/pts/26
Sep 29 17:24:27 pedri-home pptp[18767]: nm-pptp-service-18760 log[main:pptp.c:314]: The synchronous pptp option is NOT activated
Sep 29 17:24:27 pedri-home NetworkManager[912]: SCPlugin-Ifupdown: devices added (path: /sys/devices/virtual/net/ppp0, iface: ppp0)
Sep 29 17:24:27 pedri-home NetworkManager[912]: SCPlugin-Ifupdown: device added (path: /sys/devices/virtual/net/ppp0, iface: ppp0): no ifupdown configuration found.
Sep 29 17:24:27 pedri-home NetworkManager[912]: <warn> /sys/devices/virtual/net/ppp0: couldn't determine device driver; ignoring...
Sep 29 17:24:28 pedri-home pptp[18780]: nm-pptp-service-18760 log[ctrlp_rep:pptp_ctrl.c:251]: Sent control packet type is 1 'Start-Control-Connection-Request'
Sep 29 17:24:29 pedri-home pptp[18780]: nm-pptp-service-18760 log[ctrlp_disp:pptp_ctrl.c:739]: Received Start Control Connection Reply
Sep 29 17:24:29 pedri-home pptp[18780]: nm-pptp-service-18760 log[ctrlp_disp:pptp_ctrl.c:773]: Client connection established.
Sep 29 17:24:29 pedri-home pptp[18780]: nm-pptp-service-18760 log[ctrlp_rep:pptp_ctrl.c:251]: Sent control packet type is 7 'Outgoing-Call-Request'
Sep 29 17:24:29 pedri-home pptp[18780]: nm-pptp-service-18760 log[ctrlp_disp:pptp_ctrl.c:858]: Received Outgoing Call Reply.
Sep 29 17:24:29 pedri-home pptp[18780]: nm-pptp-service-18760 log[ctrlp_disp:pptp_ctrl.c:897]: Outgoing call established (call ID 0, peer's call ID 150).
Sep 29 17:24:58 pedri-home pppd[18764]: LCP: timeout sending Config-Requests
Sep 29 17:24:58 pedri-home pppd[18764]: Connection terminated.
Sep 29 17:24:58 pedri-home NetworkManager[912]: <warn> VPN plugin failed: 1
Sep 29 17:24:58 pedri-home pppd[18764]: Modem hangup
Sep 29 17:24:58 pedri-home pptp[18767]: nm-pptp-service-18760 warn[decaps_hdlc:pptp_gre.c:204]: short read (-1): Input/output error
Sep 29 17:24:58 pedri-home pptp[18767]: nm-pptp-service-18760 warn[decaps_hdlc:pptp_gre.c:216]: pppd may have shutdown, see pppd log
Sep 29 17:24:58 pedri-home pppd[18764]: Exit.
Sep 29 17:24:58 pedri-home NetworkManager[912]: message repeated 2 times: [ <warn> VPN plugin failed: 1]
Sep 29 17:24:58 pedri-home NetworkManager[912]: <info> VPN plugin state changed: stopped (6)
Sep 29 17:24:58 pedri-home NetworkManager[912]: <info> VPN plugin state change reason: 0
Sep 29 17:24:58 pedri-home NetworkManager[912]: <info> Policy set 'Wired connection 1' (eth0) as default for IPv4 routing and DNS.
Sep 29 17:24:58 pedri-home pptp[18780]: nm-pptp-service-18760 log[callmgr_main:pptp_callmgr.c:234]: Closing connection (unhandled)
Sep 29 17:24:58 pedri-home pptp[18780]: nm-pptp-service-18760 log[ctrlp_rep:pptp_ctrl.c:251]: Sent control packet type is 12 'Call-Clear-Request'
Sep 29 17:24:58 pedri-home pptp[18780]: nm-pptp-service-18760 log[call_callback:pptp_callmgr.c:79]: Closing connection (call state)
Sep 29 17:24:58 pedri-home NetworkManager[912]: <warn> error disconnecting VPN: Could not process the request because no VPN connection was active.
Sep 29 17:24:58 pedri-home NetworkManager[912]: SCPlugin-Ifupdown: devices removed (path: /sys/devices/virtual/net/ppp0, iface: ppp0)
Sep 29 17:25:03 pedri-home NetworkManager[912]: <info> VPN service 'pptp' disappeared
答え1
自宅の ADSL 接続で VPN を設定しようとしたときにも、同様の問題が発生しました。PPPoE 接続の MTU を手動に変更し、1432 に設定すると、ある程度成功しました。それでも、時々ランダムに切断されますが、作業を行うのに十分な時間保持されます...