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前些时候自己配置的一台pptp客户端无法连接了，具体症状是本地建立PPTP连接后点击连接无反应或出错.

#vi /var/log/messages

*查看系统错误报告，报告显示如下

Jan 22 19:09:40 localhost nautilus: [N-A] Nautilus-Actions Menu Extender 2.30.3 initializing...
Jan 22 19:09:45 localhost NetworkManager[2007]:  (eth0): device state change: 8 -> 3 (reason 0)
Jan 22 19:09:45 localhost NetworkManager[2007]:  (eth0): deactivating device (reason: 0).
Jan 22 19:09:45 localhost pppd[2023]: Terminating on signal 15
Jan 22 19:09:45 localhost pppd[2023]: Connect time 0.5 minutes.
Jan 22 19:09:45 localhost pppd[2023]: Sent 2408 bytes, received 4087 bytes.
Jan 22 19:09:45 localhost NetworkManager[2007]:  Activation (eth0) starting connection 'ADSL'
Jan 22 19:09:45 localhost NetworkManager[2007]:  (eth0): device state change: 3 -> 4 (reason 0)
Jan 22 19:09:45 localhost NetworkManager[2007]:  Activation (eth0) Stage 1 of 5 (Device Prepare) scheduled...
Jan 22 19:09:45 localhost NetworkManager[2007]:  Activation (eth0) Stage 1 of 5 (Device Prepare) started...
Jan 22 19:09:45 localhost NetworkManager[2007]:  Activation (eth0) Stage 2 of 5 (Device Configure) scheduled...
Jan 22 19:09:45 localhost NetworkManager[2007]:  Activation (eth0) Stage 1 of 5 (Device Prepare) complete.
Jan 22 19:09:45 localhost NetworkManager[2007]:  Activation (eth0) Stage 2 of 5 (Device Configure) starting...
Jan 22 19:09:45 localhost NetworkManager[2007]:  (eth0): device state change: 4 -> 5 (reason 0)
Jan 22 19:09:45 localhost NetworkManager[2007]:  Activation (eth0) Stage 2 of 5 (Device Configure) successful.
Jan 22 19:09:45 localhost NetworkManager[2007]:  Activation (eth0) Stage 3 of 5 (IP Configure Start) scheduled.
Jan 22 19:09:45 localhost NetworkManager[2007]:  Activation (eth0) Stage 2 of 5 (Device Configure) complete.
Jan 22 19:09:45 localhost NetworkManager[2007]:  Activation (eth0) Stage 3 of 5 (IP Configure Start) started...
Jan 22 19:09:45 localhost NetworkManager[2007]:  (eth0): device state change: 5 -> 7 (reason 0)
Jan 22 19:09:45 localhost NetworkManager[2007]:  starting PPP connection
Jan 22 19:09:45 localhost dbus: [system] Rejected send message, 2 matched rules; type="error", sender=":1.1" (uid=0 pid=2007 comm="NetworkManager) interface="(unset)" member="(unset)" error name="org.freedesktop.DBus.Error.UnknownMethod" requested_reply=0 destination=":1.6" (uid=0 pid=2023 comm="/usr/sbin/pppd))
Jan 22 19:09:45 localhost dbus: [system] Rejected send message, 2 matched rules; type="error", sender=":1.1" (uid=0 pid=2007 comm="NetworkManager) interface="(unset)" member="(unset)" error name="org.freedesktop.DBus.Error.UnknownMethod" requested_reply=0 destination=":1.6" (uid=0 pid=2023 comm="/usr/sbin/pppd))
Jan 22 19:09:45 localhost pppd[3126]: Warning: can't open options file /root/.ppprc: Permission denied
Jan 22 19:09:45 localhost pppd[3126]: Plugin rp-pppoe.so loaded.
Jan 22 19:09:45 localhost pppd[3126]: RP-PPPoE plugin version 3.8p compiled against pppd 2.4.5
Jan 22 19:09:45 localhost NetworkManager[2007]:  pppd started with pid 3126
Jan 22 19:09:45 localhost NetworkManager[2007]:  Activation (eth0) Stage 3 of 5 (IP Configure Start) complete.
Jan 22 19:09:45 localhost pppd[3126]: Plugin /usr/lib/pppd/2.4.5/nm-pppd-plugin.so loaded.
Jan 22 19:09:45 localhost dbus: [system] Rejected send message, 2 matched rules; type="error", sender=":1.1" (uid=0 pid=2007 comm="NetworkManager) interface="(unset)" member="(unset)" error name="org.freedesktop.DBus.Error.UnknownMethod" requested_reply=0 destination=":1.6" (uid=0 pid=2023 comm="/usr/sbin/pppd))
Jan 22 19:09:45 localhost pppd[2023]: Connection terminated.
Jan 22 19:09:45 localhost dbus: [system] Rejected send message, 2 matched rules; type="error", sender=":1.1" (uid=0 pid=2007 comm="NetworkManager) interface="(unset)" member="(unset)" error name="org.freedesktop.DBus.Error.UnknownMethod" requested_reply=0 destination=":1.6" (uid=0 pid=2023 comm="/usr/sbin/pppd))
Jan 22 19:09:45 localhost pppd[3126]: pppd 2.4.5 started by root, uid 0
Jan 22 19:09:45 localhost dbus: [system] Rejected send message, 2 matched rules; type="error", sender=":1.1" (uid=0 pid=2007 comm="NetworkManager) interface="(unset)" member="(unset)" error name="org.freedesktop.DBus.Error.UnknownMethod" requested_reply=0 destination=":1.6" (uid=0 pid=2023 comm="/usr/sbin/pppd))
Jan 22 19:09:45 localhost pppd[3126]: PPP session is 9892
Jan 22 19:09:45 localhost pppd[3126]: Connected to 00:46:4b:ad:da:b6 via interface eth0
Jan 22 19:09:45 localhost pppd[3126]: Using interface ppp0
Jan 22 19:09:45 localhost pppd[3126]: Connect: ppp0 < --> eth0
Jan 22 19:09:45 localhost pppd[2023]: Exit.
Jan 22 19:09:45 localhost pppd[3126]: Remote message: Authentication success,Welcome!
Jan 22 19:09:45 localhost pppd[3126]: PAP authentication succeeded
Jan 22 19:09:45 localhost pppd[3126]: peer from calling number 00:46:4B:AD:DA:B6 authorized
Jan 22 19:09:45 localhost pppd[3126]: local  IP address 112.66.50.113
Jan 22 19:09:45 localhost pppd[3126]: remote IP address 112.66.50.1
Jan 22 19:09:45 localhost pppd[3126]: primary   DNS address 202.100.199.8
Jan 22 19:09:45 localhost pppd[3126]: secondary DNS address 202.100.192.68
Jan 22 19:09:45 localhost NetworkManager[2007]:  PPP manager(IP Config Get) reply received.
Jan 22 19:09:45 localhost NetworkManager[2007]:  Activation (eth0) Stage 4 of 5 (IP4 Configure Get) scheduled...
Jan 22 19:09:45 localhost NetworkManager[2007]:  Activation (eth0) Stage 4 of 5 (IP4 Configure Get) started...
Jan 22 19:09:45 localhost NetworkManager[2007]:  Activation (eth0) Stage 5 of 5 (IP Configure Commit) scheduled...
Jan 22 19:09:45 localhost NetworkManager[2007]:  Activation (eth0) Stage 4 of 5 (IP4 Configure Get) complete.
Jan 22 19:09:45 localhost NetworkManager[2007]:  Activation (eth0) Stage 5 of 5 (IP Configure Commit) started...
Jan 22 19:09:46 localhost NetworkManager[2007]:  (eth0): device state change: 7 -> 8 (reason 0)
Jan 22 19:09:46 localhost NetworkManager[2007]:  Policy set 'ADSL' (ppp0) as default for IPv4 routing and DNS.
Jan 22 19:09:46 localhost NetworkManager[2007]:  Activation (eth0) successful, device activated.
Jan 22 19:09:46 localhost NetworkManager[2007]:  Activation (eth0) Stage 5 of 5 (IP Configure Commit) complete.
Jan 22 19:09:47 localhost tpvmlpd2[3198]: device type not supported
Jan 22 19:09:50 localhost NetworkManager[2007]:  Starting VPN service 'org.freedesktop.NetworkManager.pptp'...
Jan 22 19:09:50 localhost NetworkManager[2007]:  VPN service 'org.freedesktop.NetworkManager.pptp' started (org.freedesktop.NetworkManager.pptp), PID 3200
Jan 22 19:09:50 localhost NetworkManager[2007]:  VPN service 'org.freedesktop.NetworkManager.pptp' appeared, activating connections
Jan 22 19:09:50 localhost NetworkManager[2007]:  VPN plugin state changed: 1
Jan 22 19:09:50 localhost NetworkManager[2007]:  VPN plugin state changed: 3
Jan 22 19:09:50 localhost NetworkManager[2007]:  VPN connection 'PPTP' (Connect) reply received.
Jan 22 19:09:50 localhost NetworkManager[2007]:  VPN connection 'PPTP' failed to connect: 'No VPN secrets!'.
Jan 22 19:09:50 localhost NetworkManager[2007]:  error disconnecting VPN: Could not process the request because no VPN connection was active.
Jan 22 19:09:50 localhost NetworkManager[2007]:  Policy set 'ADSL' (ppp0) as default for IPv4 routing and DNS.
Jan 22 19:10:02 localhost tpvmlpd2[3223]: device type not supported
Jan 22 19:10:17 localhost tpvmlpd2[3227]: device type not supported
Jan 22 19:10:32 localhost tpvmlpd2[3231]: device type not supported
Jan 22 19:10:47 localhost tpvmlpd2[3235]: device type not supported

 
原本以为是服务器端的问题，也曾怀疑过是高墙的原因，甚至还以为是Centos6.3系统的问题，后来在一些朋友的提醒下才知道，原来是自己的加密协议有问题，不是服务器端，不是本地系统的问题.
如图设置即可