我有一个工作的pptpd + pppd服务器configuration，目前有两个Windows 7客户端成功连接。 然而，当我尝试连接一个Linux客户端时，我得到了一个非常奇怪的交换，在服务器端和客户端都以“peer refused to authenticate”结束。
这是来自服务器的日志：
pppd[8205]: using channel 51 pppd[8205]: sent [LCP ConfReq id=0x1 <asyncmap 0x0> <auth chap MS-v2> <magic 0x20b0750f> <pcomp> <accomp>] pppd[8205]: rcvd [LCP ConfRej id=0x1 <auth chap MS-v2>] pppd[8205]: sent [LCP ConfReq id=0x2 <asyncmap 0x0> <magic 0x20b0750f> <pcomp> <accomp>] pppd[8205]: rcvd [LCP ConfAck id=0x2 <asyncmap 0x0> <magic 0x20b0750f> <pcomp> <accomp>] pppd[8205]: rcvd [LCP ConfReq id=0x1 <asyncmap 0x0> <auth chap MS-v2> <magic 0x23d6bed3> <pcomp> <accomp>] pppd[8205]: sent [LCP ConfNak id=0x1 <auth pap>] pppd[8205]: rcvd [LCP ConfReq id=0x2 <asyncmap 0x0> <magic 0x23d6bed3> <pcomp> <accomp>] pppd[8205]: sent [LCP ConfAck id=0x2 <asyncmap 0x0> <magic 0x23d6bed3> <pcomp> <accomp>] pppd[8205]: sent [LCP EchoReq id=0x0 magic=0x20b0750f] pppd[8205]: sent [LCP TermReq id=0x3 "peer refused to authenticate"] pppd[8205]: rcvd [LCP EchoReq id=0x0 magic=0x23d6bed3] pppd[8205]: rcvd [LCP TermReq id=0x3 "peer refused to authenticate"] pppd[8205]: sent [LCP TermAck id=0x3] pppd[8205]: rcvd [LCP TermAck id=0x3] pptpd[8204]: CTRL: Reaping child PPP[8205] 这是客户端的日志：
pppd[12077]: pppd options in effect: pppd[12077]: debug # (from command line) pppd[12077]: holdoff 10 # (from /etc/ppp/peers/home1) pppd[12077]: persist # (from /etc/ppp/peers/home1) pppd[12077]: dump # (from command line) pppd[12077]: require-mschap-v2 # (from /etc/ppp/peers/home1) pppd[12077]: refuse-pap # (from /etc/ppp/peers/home1) pppd[12077]: refuse-mschap # (from /etc/ppp/peers/home1) pppd[12077]: name <redacted> # (from /etc/ppp/peers/home1) pppd[12077]: remotename <redacted> # (from /etc/ppp/peers/home1) pppd[12077]: # (from /etc/ppp/options) pppd[12077]: pty pptp <redacted> --nolaunchpppd # (from /etc/ppp/peers/home1) pppd[12077]: crtscts # (from /etc/ppp/options) pppd[12077]: # (from /etc/ppp/options) pppd[12077]: asyncmap 0 # (from /etc/ppp/options) pppd[12077]: lcp-echo-failure 4 # (from /etc/ppp/options) pppd[12077]: lcp-echo-interval 30 # (from /etc/ppp/options) pppd[12077]: hide-password # (from /etc/ppp/options) pppd[12077]: proxyarp # (from /etc/ppp/options) pppd[12077]: nobsdcomp # (from /etc/ppp/peers/home1) pppd[12077]: nodeflate # (from /etc/ppp/peers/home1) pppd[12077]: nomppe # (from /etc/ppp/peers/home1) pppd[12077]: noipx # (from /etc/ppp/options) pppd[12078]: pppd 2.4.5 started by <redacted>, uid 0 pppd[12078]: using channel 12 pppd[12078]: Using interface ppp0 pppd[12078]: Connect: ppp0 <--> /dev/pts/14 pptp[12079]: anon log[main:pptp.c:314]: The synchronous pptp option is NOT activated pptp[12086]: anon log[ctrlp_rep:pptp_ctrl.c:251]: Sent control packet type is 1 'Start-Control-Connection-Request' pptp[12086]: anon log[ctrlp_disp:pptp_ctrl.c:739]: Received Start Control Connection Reply pptp[12086]: anon log[ctrlp_disp:pptp_ctrl.c:773]: Client connection established. pppd[12078]: sent [LCP ConfReq id=0x1 <asyncmap 0x0> <auth chap MS-v2> <magic 0x23d6bed3> <pcomp> <accomp>] pptp[12086]: anon log[ctrlp_rep:pptp_ctrl.c:251]: Sent control packet type is 7 'Outgoing-Call-Request' pptp[12086]: anon log[ctrlp_disp:pptp_ctrl.c:858]: Received Outgoing Call Reply. pptp[12086]: anon log[ctrlp_disp:pptp_ctrl.c:897]: Outgoing call established (call ID 0, peer's call ID 1920). pppd[12078]: rcvd [LCP ConfReq id=0x1 <asyncmap 0x0> <auth chap MS-v2> <magic 0x20b0750f> <pcomp> <accomp>] pppd[12078]: No auth is possible pppd[12078]: sent [LCP ConfRej id=0x1 <auth chap MS-v2>] pppd[12078]: rcvd [LCP ConfReq id=0x2 <asyncmap 0x0> <magic 0x20b0750f> <pcomp> <accomp>] pppd[12078]: sent [LCP ConfAck id=0x2 <asyncmap 0x0> <magic 0x20b0750f> <pcomp> <accomp>] pppd[12078]: sent [LCP ConfReq id=0x1 <asyncmap 0x0> <auth chap MS-v2> <magic 0x23d6bed3> <pcomp> <accomp>] pppd[12078]: rcvd [LCP ConfNak id=0x1 <auth pap>] pppd[12078]: sent [LCP ConfReq id=0x2 <asyncmap 0x0> <magic 0x23d6bed3> <pcomp> <accomp>] pppd[12078]: rcvd [LCP ConfAck id=0x2 <asyncmap 0x0> <magic 0x23d6bed3> <pcomp> <accomp>] pppd[12078]: sent [LCP EchoReq id=0x0 magic=0x23d6bed3] pppd[12078]: peer refused to authenticate: terminating link pppd[12078]: sent [LCP TermReq id=0x3 "peer refused to authenticate"] pppd[12078]: rcvd [LCP EchoReq id=0x0 magic=0x20b0750f] pppd[12078]: rcvd [LCP TermReq id=0x3 "peer refused to authenticate"] pppd[12078]: sent [LCP TermAck id=0x3] pppd[12078]: rcvd [LCP TermAck id=0x3] pppd[12078]: Connection terminated.
我真的很困惑这些线（从服务器日志）：
pppd[8205]: sent [LCP ConfReq id=0x1 <asyncmap 0x0> <auth chap MS-v2> <magic 0x20b0750f> <pcomp> <accomp>] pppd[8205]: rcvd [LCP ConfRej id=0x1 <auth chap MS-v2>] pppd[8205]: sent [LCP ConfReq id=0x2 <asyncmap 0x0> <magic 0x20b0750f> <pcomp> <accomp>] pppd[8205]: rcvd [LCP ConfAck id=0x2 <asyncmap 0x0> <magic 0x20b0750f> <pcomp> <accomp>] pppd[8205]: rcvd [LCP ConfReq id=0x1 <asyncmap 0x0> <auth chap MS-v2> <magic 0x23d6bed3> <pcomp> <accomp>] pppd[8205]: sent [LCP ConfNak id=0x1 <auth pap>] pppd[8205]: rcvd [LCP ConfReq id=0x2 <asyncmap 0x0> <magic 0x23d6bed3> <pcomp> <accomp>]
如果我读的是正确的，服务器请求mschap-v2 auth，那么客户端拒绝（为什么？）; 之后，客户端请求mschap-v2 auth，那么服务器将拒绝pap（wtf？），导致两个对等方都不进行身份validation，连接失败。
有人可以点亮这里发生的事情吗？
弄清楚了。
问题是给客户端上的“auth”和“require-mschap-v2”选项给pppd。 显然，只有服务器端必须configuration为请求authentication与configuration不要求任何forms的authentication的客户端。 发生了什么事是客户端要求服务器进行身份validation，失败了。
我希望我的经验能帮助别人到达这里。
当我得到这种沟通的时候，我发现了这个问题最常见的原因：
pppd[8205]: sent [LCP ConfReq id=0x1 <asyncmap 0x0> <auth chap MS-v2> <magic 0x20b0750f> <pcomp> <accomp>] pppd[8205]: rcvd [LCP ConfRej id=0x1 <auth chap MS-v2>] pppd[8205]: sent [LCP ConfReq id=0x2 <asyncmap 0x0> <magic 0x20b0750f> <pcomp> <accomp>] pppd[8205]: rcvd [LCP ConfAck id=0x2 <asyncmap 0x0> <magic 0x20b0750f> <pcomp> <accomp>] pppd[8205]: rcvd [LCP ConfReq id=0x1 <asyncmap 0x0> <auth chap MS-v2> <magic 0x23d6bed3> <pcomp> <accomp>] pppd[8205]: sent [LCP ConfNak id=0x1 <auth pap>] pppd[8205]: rcvd [LCP ConfReq id=0x2 <asyncmap 0x0> <magic 0x23d6bed3> <pcomp> <accomp>]
…是没有正确到达目的地的GRE数据包。
注意日志中的sent和rcvd行：有某种通信，但还不够。
许多路由器不允许GRE数据包 （PPTP必须使用）穿越它们，但其中大多数路由器都有一些选项来启用/禁用它。
在我的情况下（NetGear Genie CG3100D电缆调制解调器），你可以解决它检查：
Advanced --> Advanced Configuration --> Services -> PPTP PassThrough